This work was supported by the Bill and Melinda Gates Foundation (PneuCarriage project, Grant 52099) and the Victorian Government&#8217;s Operational Infrastructure Support Program.&#160;Thanks to Eileen Dunne, Janet Strachan, and Kim Hare for critical reading of the manuscript.

1. Preparation of Cell Suspension for Typing
<ol>
	<li>Using a sterile disposable 1 &#181;l loop, take a small sweep of fresh overnight pure culture of pneumococci grown on solid nonselective horse blood agar and inoculate 100 &#181;l Heart Infusion (HI) broth. The suspension should appear to be just visibly turbid. Gently agitate the tube to emulsify. 
	Note: Other media such as Brain Heart Infusion broth may also be suitable. Addition of serum (e.g. a final concentration of 10% (v/v) horse serum) and incubation at 37 &#176;C for approximately 1 hr before use may be used to enhance the reaction.</li>
</ol>
2. Checking Density of Cell Suspension
The cell suspension prepared in step 1.1 will also be used as the negative control, and should be checked for cell density before adding the typing sera.
<ol>
	<li>Using a 1 &#181;l loop, transfer a drop of the inoculum prepared in step 1.1 onto a glass microscope slide.</li>
	<li>Using a pair of forceps, place a small circular coverslip on the suspension.</li>
	<li>Using phase-contrast setting, observe the preparation microscopically under 400X magnification, to check the density of the suspension (Figure 1A).
	<ol>
		<li>If the inoculum is too heavy&#160;(Figure 2A), add more broth to the cell suspension made in step 1.1 to dilute it. Gently mix again.</li>
		<li>If the inoculum is too light, for example, there are &#60;50 cells visible in the microscopic field&#160;(Figure 2B), add more bacteria to the cell suspension preparation made in step 1.1 and gently mix. 
		Note: With experience, the density of the cell suspension can be judged by shaking and holding up to the light, where it should appear to be just visibly turbid.</li>
	</ol>
	</li>
	<li>Repeat steps 2.1-2.3 until a suitable number of cells are visible in the microscopic field. 
	Note: Glass slides and coverslips present a sharps hazard. After use, slides and coverslips are contaminated with infectious material and must be disposed into a biohazard sharps container.</li>
</ol>
3. Typing
<ol>
	<li>Transfer ~1 &#181;l of the prepared inoculum (e.g. using a 1 &#181;l loop) onto the glass microscope slide. Discard the loop into the biohazard sharps container.</li>
	<li>Add an equal volume (1 &#181;l loopful) of room-temperature antiserum onto the slide and mix both drops well with the loop.</li>
	<li>Using a pair of forceps, place a small circular coverslip on the suspension, taking care not to touch the drop. Place the coverslip on the suspension immediately after the addition of antisera to prevent the fluid on the slide from drying out.</li>
	<li>Using a microscope, observe the suspension under phase-contrast with 400X magnification. A negative Quellung reaction is observed when little or no &#8216;swelling&#8217; of the pneumococcal cells can be seen at 400X magnification, similar to what is observed in the pneumococcal cell suspension with no antisera added (negative control). A positive Quellung reaction is observed when the cells appear enlarged or &#39;swollen&#39; and more visible when compared to the cells in the negative control. 
	Note: Equivocal reactions should be investigated further, for example by examining the reaction after 5-10 min incubation at room temperature, or by repeating the reaction with more antiserum.</li>
	<li>Conduct pneumococcal serotyping with successive testing of individual antisera pools until a positive reaction is observed. Alternatively, pools can be applied in &#8216;rounds&#8217; depending upon local incidence of serotypes. 
	Note: Testing in &#8216;rounds&#8217; ensures that the pools containing antibodies to the most common serotypes are tested first, minimizing effort and cost. Concurrent testing of several pools also provides additional negative controls, which can be useful in interpretation. If all the pools in a particular &#8216;round&#8217; are negative, test the isolate with subsequent rounds of pools.</li>
	<li>Test the isolate using the appropriate type or group antiserum contained within the reactive pool. Where appropriate, use factor antisera to further differentiate the serotype. 
	Note: Keys to pneumococcal antisera supplied by the manufacturer are used in the selection of appropriate pool, type, group or factor antisera and interpretation of results (including any cross-reactions).</li>
	<li>If negative results are obtained with all pools, test the isolate with Omniserum reagent (contains antibodies against 91 serotypes21). If a positive Quellung reaction is still not observed when testing a pneumococcal isolate with the Omniserum reagent, this may be because the isolate is expressing little or no capsule, or that antibodies against the serotype are not represented in the Omniserum. The latter category may include new serotypes.</li>
</ol>

<ol>
	<li>O'Brien, K. L., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Burden+of+disease+caused+by+Streptococcus+pneumoniae+in+children+younger+than+5+years:+global+estimates.">Burden of disease caused by Streptococcus pneumoniae in children younger than 5 years: global estimates.</a> Lancet. 374, 893-902 (2009).</li><li>Bogaert, D., De Groot, R., Hermans, P. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Streptococcus+pneumoniae+colonisation:+the+key+to+pneumococcal+disease.">Streptococcus pneumoniae colonisation: the key to pneumococcal disease.</a> Lancet Infect. Dis. 4, 144-154 (2004).</li><li>Henrichsen, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Six+newly+recognized+types+of+Streptococcus+pneumoniae.">Six newly recognized types of Streptococcus pneumoniae.</a> J. Clin. Microbiol. 33, 2759-2762 (1995).</li><li>Calix, J. J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Biochemical,+genetic,+and+serological+characterization+of+two+capsule+subtypes+among+Streptococcus+pneumoniae+Serotype+20+strains:+discovery+of+a+new+pneumococcal+serotype.">Biochemical, genetic, and serological characterization of two capsule subtypes among Streptococcus pneumoniae Serotype 20 strains: discovery of a new pneumococcal serotype.</a> J. Biol. Chem. 287, 27885-27894 (2012).</li><li>Hausdorff, W. P., Bryant, J., Paradiso, P. R., Siber, G. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Which+pneumococcal+serogroups+cause+the+most+invasive+disease:+implications+for+conjugate+vaccine+formulation+and+use,+part+I.">Which pneumococcal serogroups cause the most invasive disease: implications for conjugate vaccine formulation and use, part I.</a> Clin. Infect. Dis. 30, 100-121 (2000).</li><li>Johnson, H. L., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Systematic+evaluation+of+serotypes+causing+invasive+pneumococcal+disease+among+children+under+five:+the+pneumococcal+global+serotype+project.">Systematic evaluation of serotypes causing invasive pneumococcal disease among children under five: the pneumococcal global serotype project.</a> PLoS Med. 8, (2010).</li><li>Weinberger, D. M., Malley, R., Lipsitch, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Serotype+replacement+in+disease+after+pneumococcal+vaccination.">Serotype replacement in disease after pneumococcal vaccination.</a> Lancet. 378, 1962-1973 (2011).</li><li>Obaro, S. K., Adegbola, R. A., Banya, W. A., Greenwood, B. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Carriage+of+pneumococci+after+pneumococcal+vaccination.">Carriage of pneumococci after pneumococcal vaccination.</a> Lancet. 348, 271-272 (1996).</li><li>Mulholland, K., Satzke, C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Serotype+replacement+after+pneumococcal+vaccination.">Serotype replacement after pneumococcal vaccination.</a> Lancet. 379, 1388-1389 (2012).</li><li>Austrian, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+quellung+reaction,+a+neglected+microbiologic+technique.">The quellung reaction, a neglected microbiologic technique.</a> Mt. Sinai. J. Med. 43, 699-709 (1976).</li><li>Konradsen, H. B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Validation+of+serotyping+of+Streptococcus+pneumoniae+in+Europe.">Validation of serotyping of Streptococcus pneumoniae in Europe.</a> Vaccine. 23, 1368-1373 (2005).</li><li>Lovgren, M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Evolution+of+an+international+external+quality+assurance+model+to+support+laboratory+investigation+of+Streptococcus+pneumoniae,+developed+for+the+SIREVA+project+in+Latin+America,+from.">Evolution of an international external quality assurance model to support laboratory investigation of Streptococcus pneumoniae, developed for the SIREVA project in Latin America, from.</a> J. Clin. Microbiol. 45, 3184-3190 (2007).</li><li>Reasonover, A., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+International+Circumpolar+Surveillance+interlaboratory+quality+control+program+for+Streptococcus+pneumoniae.">The International Circumpolar Surveillance interlaboratory quality control program for Streptococcus pneumoniae.</a> J. Clin. Microbiol. 49, 138-143 (2011).</li><li>Hare, K. M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=#34;Dodgy+6As&amp;#34;:+differentiating+pneumococcal+serotype+6C+from+6A+by+use+of+the+Quellung+reaction.">#34;Dodgy 6As&amp;#34;: differentiating pneumococcal serotype 6C from 6A by use of the Quellung reaction.</a> J. Clin. Microbiol. 47, 1981-1982 (2009).</li><li>Kong, F., Gilbert, G. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Using+cpsA-cpsB+sequence+polymorphisms+and+serotype-/group-specific+PCR+to+predict+51+Streptococcus+pneumoniae+capsular+serotypes.">Using cpsA-cpsB sequence polymorphisms and serotype-/group-specific PCR to predict 51 Streptococcus pneumoniae capsular serotypes.</a> J. Med. Microbiol. 52, 1047-1058 (2003).</li><li>Castillo, D., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Identification+and+characterization+of+Streptococcus+pneumoniae.">Identification and characterization of Streptococcus pneumoniae.</a> Laboratory Methods for the Diagnosis of Meningitis caused by Neisseria meningitidis, Streptococcus pneumoniae, and Haemophilus influenzae. 2nd ed. , 73-86 (2011).</li><li>Kaijalainen, T., Rintamaki, S., Herva, E., Leinonen, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Evaluation+of+gene-technological+and+conventional+methods+in+the+identification+of+Streptococcus+pneumoniae.">Evaluation of gene-technological and conventional methods in the identification of Streptococcus pneumoniae.</a> J. Microbiol. Methods. 51, 111-118 (2002).</li><li>Sorensen, U. B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Typing+of+pneumococci+by+using+12+pooled+antisera.">Typing of pneumococci by using 12 pooled antisera.</a> J. Clin. Microbiol. 31, 2097-2100 (1993).</li><li>Diagnostica SSI, <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Key+to+pneumococcal+factor+antisera.">Key to pneumococcal factor antisera.</a> , (2013).</li><li>Diagnostica SSI, <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Pneumococcal+antisera+for+in+vitro+diagnostic+use.">Pneumococcal antisera for in vitro diagnostic use.</a> , (2011).</li><li>Lund, E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Laboratory+diagnosis+of+Pneumococcus+infections.">Laboratory diagnosis of Pneumococcus infections.</a> Bull. World Health Organ. 23, 5-13 (1960).</li><li>Satzke, C., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Standard+method+for+detecting+upper+respiratory+carriage+of+Streptococcus+pneumoniae:+Updated+recommendations+from+the+World+Health+Organization+Pneumococcal+Carriage+Working+Group.">Standard method for detecting upper respiratory carriage of Streptococcus pneumoniae: Updated recommendations from the World Health Organization Pneumococcal Carriage Working Group.</a> Vaccine. 32, 165-179 (2013).</li><li>Vernet, G., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Laboratory-based+diagnosis+of+pneumococcal+pneumonia:+state+of+the+art+and+unmet+needs.">Laboratory-based diagnosis of pneumococcal pneumonia: state of the art and unmet needs.</a> Clin. Microbiol. Infect. 17, 1-13 (2011).</li><li>Casewell, M. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Experiences+in+the+use+of+commercial+antisera+for+the+capsular+typing+of+klebsiella+species.">Experiences in the use of commercial antisera for the capsular typing of klebsiella species.</a> J. Clin. Pathol. 25, 734-737 (1972).</li></ol>

The authors have nothing to disclose.

A critical step in this technique is ensuring a pure culture is used to prepare the suspension along with adding a suitable number of bacterial cells to the broth. It should be noted that colony growth and morphology on agar plates varies between different pneumococcal isolates. Some produce dry and rough colonies, which can be difficult to pick off with a loop and do not emulsify well in the broth. For this reason, a larger sweep of bacteria may be required when preparing the cell suspension. In any case, it is imperative that individual cells, and not aggregates, are obvious in the negative control so their relative size can be compared to the cells with antisera added. Additionally, too many bacterial cells may result in a false negative reaction, where an excess of capsular antigen may inhibit the Quellung reaction10. For this reason, it is important to create a bacterial suspension with a suitable cell density (Figure 1). The suspension may be preserved for several months by the addition of several drops of concentrated formalin. This enables easier batch testing and also sterilizes the broth reducing the risk of laboratory-acquired infections; although this must be weighed against the safety risk of handling formalin, which is toxic, corrosive, carcinogenic, sensitizing, and flammable. In addition, we have observed that some isolates show weaker reactions in the presence of formalin (data not shown).
Quellung reactions are examined using a microscope. The use of phase contrast enhances the visibility of the capsule. In some laboratories, the reaction is viewed using oil-immersion at 1,000X magnification14,16.&#160; In addition, some laboratories use a counter stain (methylene blue) to further enhance the visibility of a positive reaction10,16,22. The method presented here is viewed without oil-immersion and under 400X magnification15,17. This method is quick, simple and relatively easy to read23.
It is important to maintain good internal quality control procedures to ensure the antisera and testing procedures are in order. Participation in an external quality assurance program is often beneficial.
A major limitation of the Quellung reaction for serotyping of pneumococci is the high cost of the antisera required. However, this is minimized in the above protocol due to the small amount of antiserum used for each reaction. Several other methods have been described for serotyping pneumococci23,24. However, Quellung remains the gold standard and the development of new methods requires standardization against the Quellung reaction23.&#160; Using appropriate antisera, the Quellung reaction can also be utilized to identify and type other capsule producing bacteria25. The Quellung reaction is instrumental in the characterization of current and emerging pneumococcal serotypes, as well as providing information on vaccine efficacy and the long-term impact of vaccination on carriage and disease.

Streptococcus pneumoniae (the pneumococcus) is responsible for the death of an estimated 800,000 children under the age of five annually, with the burden of disease falling predominantly in resource-poor countries1. Pneumococcal diseases range in severity from localized infections such as acute otitis media to severe life threatening infections such as sepsis, meningitis and pneumonia2. Over 90 capsular serotypes of pneumococci have been described3,4. Current pneumococcal vaccines provide protection against the serotypes that are responsible for the majority of invasive disease5,6. However, widespread use of vaccines has been associated with replacement of serotypes included in the vaccine by nonvaccine serotypes, both in nasopharyngeal carriage and invasive disease7,8. This highlights the importance of serotyping for epidemiological surveillance and long-term vaccine impact studies9.
The gold standard method for pneumococcal typing is the capsular reaction test, known as the Quellung reaction, first described by Neufeld in 1902 (see Austrian10). A high degree of concordance has been found between laboratories, and between the Quellung reaction and other serotyping methods11-13. There are several variations of the Quellung reaction10,14-16. &#160;The method described here does not require the use of a counter stain or the oil immersion lens; rather, a drop of prepared specimen is mixed with the typing serum and examined immediately under 400X magnification.
The Quellung reaction is usually performed using commercially available antisera. The method described here uses less antisera compared with some other methods16,17, making it more cost effective. Once an isolate is identified as a pneumococcus, it is sequentially tested with antisera pools until a positive reaction is observed. Each pool antiserum contains different mixtures of antisera raised against 91 pneumococcal serotypes18. Once the pool is established, the individual type and group antisera that are included in the reactive pool are tested individually in sequence. Type antisera generally react with a single serotype (e.g. Type 1 antiserum reacts with serotype 1), whereas group antisera react with all the serotypes in a particular group (e.g. Group 22 antiserum reacts with serotypes 22F and 22A). Some serotypes within groups are further differentiated using factor antisera (e.g. Serotype 22F reacts with factor 22b, but not 22c). In this case testing is continued with all relevant factor antisera until serotype is determined19,20. The Quellung reaction is simple and quick14 and can be performed in any laboratory that is equipped with a good quality microscope and appropriate set of antisera.

<table><tbody><tr><td>Pneumococcus (Neufeld) antisera</td><td>SSI Diagnostica</td><td></td><td>&lt;a href=&quot;http://www.ssi.dk/ssidiagnostica&quot;&gt;http://www.ssi.dk/ssidiagnostica&lt;/a&gt;&lt;br/&gt; Bring all antisera to room temperature before use</td></tr><tr><td>Pneumococcus (Omni) antiserum</td><td>SSI Diagnostica</td><td>2438</td><td>Bring all antisera to room temperature before use</td></tr><tr><td>Optical Microscope</td><td>Leica Microsystems</td><td>Leica DML</td><td></td></tr><tr><td>Calibrated Disposable Inoculating Loops 1 &amp;micro;l</td><td>Copan</td><td>CD175S01</td><td></td></tr><tr><td>Horse Blood Agar (HBA) plates</td><td>Thermo Fisher Scientific</td><td>PP2001</td><td>&lt;a href=&quot;http://www.thermofisher.com.au/&quot;&gt;http://www.thermofisher.com.au/&lt;/a&gt;&lt;br/&gt; Bring to room temperature before use</td></tr><tr><td>Heart Infusion (HI) broth</td><td>Media Preparation Unit (MPU), The University of Melbourne</td><td>40HIN</td><td>Bring to room temperature before use</td></tr><tr><td>Glass microscope slides 76 mm x 26 mm</td><td>Lomb Scientific</td><td>7101</td><td>Sharps hazard: Dispose in a biohazard sharps container</td></tr><tr><td>Circular glass coverslips</td><td>NeuVitro</td><td>GG-5</td><td></td></tr><tr><td>*Excluding the antisera, all other materials can be purchased from alternative suppliers</td><td></td><td></td><td></td></tr><tr><td>*Plates prepared from defibranated sheep blood are suitable but blood plates prepared from citrated blood or human blood are not</td><td></td><td></td><td></td></tr></tbody></table>

capsular serotyping of streptococcus pneumoniae using the quellung reaction

There are over 90 different capsular serotypes of Streptococcus pneumoniae (the pneumococcus). As well as being a tool for understanding pneumococcal epidemiology, capsular serotyping can provide useful information for vaccine efficacy and impact studies.&#160;The Quellung reaction is the gold standard method for pneumococcal capsular serotyping. The method involves testing a pneumococcal cell suspension with pooled and specific antisera directed against the capsular polysaccharide. The antigen-antibody reactions are observed microscopically. The protocol has three main steps: 1) preparation of a bacterial cell suspension, 2) mixing of cells and antisera on a glass slide, and 3) reading the Quellung reaction using a microscope. The Quellung reaction is reasonably simple to perform and can be applied wherever a suitable microscope and antisera are available.

A positive Quellung reaction occurs when type-specific antibody binds to the capsule of the pneumococcus, leading to a change in its refractive index10. When viewed under a microscope, the bacteria appear &#8216;swollen&#8217; and more visible14. Figure 1A shows pneumococcal cells in HI broth. When type-specific anti-serum is added to the bacterial suspension, pneumococci appear &#8216;swollen&#8217;, refractive and more rounded (Figure 1B).
Too many bacterial cells added to the broth may result in aggregation of cells or a false negative reaction. Figure 2 shows inocula of pneumococcal cells in HI broth that are &#8216;too heavy&#8217; (Figure 2A) or &#8216;too light&#8217; (Figure 2B).
<img alt="Figure 1" fo:content-width="5in" fo:src="/files/ftp_upload/51208/51208fig1highres.jpg" src="/files/ftp_upload/51208/51208fig1.jpg" /> 
Figure 1.&#160;Negative and positive Quellung reaction. Preparations of serotype 9V pneumococcal isolate with no antiserum (1A) and with group 9 antiserum (1B), were viewed under 400X magnification. The latter shows the &#8216;swelling&#8217; and rounding of bacterial cells typically seen in a positive Quellung reaction.
<img alt="Figure 2" fo:content-width="5in" fo:src="/files/ftp_upload/51208/51208fig2highres.jpg" src="/files/ftp_upload/51208/51208fig2.jpg" /> 
Figure 2.&#160;Too heavy and too light inocula. Preparations of pneumococcal cell suspensions that are too heavy (2A) or too light (2B), when viewed under 400X magnification.

Watch this Scientific Journal Video about Capsular Serotyping of Streptococcus pneumoniae Using the Quellung Reaction at JoVE.com

Capsular Serotyping of Streptococcus pneumoniae Using the Quellung Reaction

The Quellung reaction is the gold standard technique for serotyping Streptococcus pneumoniae. This technique utilizes a microscope and specific pneumococcal antisera and is commonly used in reference and research laboratories worldwide.

Capsular Serotyping of Streptococcus pneumoniae Using the Quellung Reaction

There are over 90 different capsular serotypes of Streptococcus pneumoniae (the pneumococcus). As well as being a tool for understanding pneumococcal ...

capsular-serotyping-streptococcus-pneumoniae-using-quellung

Nanyang Technological University

Research

JoVE Journal

Immunology and Infection

45.4K Views.  Murdoch Childrens Research Institute. The Quellung reaction is the gold standard technique for serotyping Streptococcus pneumoniae. This technique utilizes a microscope and specific pneumococcal antisera and is commonly used in reference and research laboratories worldwide.

Video: Capsular Serotyping of Streptococcus pneumoniae Using the Quellung Reaction

An Allelotyping PCR for Identifying Salmonella enterica serovars Enteritidis, Hadar, Heidelberg, and Typhimurium

Current commercial PCRs tests for identifying Salmonella target genes unique to this genus. However, there are two species, six subspecies, and over 2,500 different Salmonella serovars, and not all are equal in their significance to public health. For example, finding S. enterica subspecies IIIa Arizona on a table egg layer farm is insignificant compared to the isolation of S. enterica subspecies I serovar Enteritidis, the leading cause of salmonellosis linked to the consumption of table eggs. Serovars are identified based on antigenic differences in lipopolysaccharide (LPS)(O antigen) and flagellin (H1 and H2 antigens). These antigenic differences are the outward appearance of the diversity of genes and gene alleles associated with this phenotype.
We have developed an allelotyping, multiplex PCR that keys on genetic differences between four major S. enterica subspecies I serovars found in poultry and associated with significant human disease in the US. The PCR primer pairs were targeted to key genes or sequences unique to a specific Salmonella serovar and designed to produce an amplicon with size specific for that gene or allele. Salmonella serovar is assigned to an isolate based on the combination of PCR test results for specific LPS and flagellin gene alleles. The multiplex PCRs described in this article are specific for the detection of S. enterica subspecies I serovars Enteritidis, Hadar, Heidelberg, and Typhimurium.
Here we demonstrate how to use the multiplex PCRs to identify serovar for a Salmonella isolate.

An Allelotyping PCR for Identifying Salmonella enterica serovars Enteritidis, Hadar, Heidelberg, and Typhimurium

We describe a multiplex PCR for the rapid detection of Salmonella enterica serovars Enteritidis, Hadar, Heidelberg, and Typhimurium. Specific Salmonella serovars can be identified by targeting a multiplex PCR to genes and sequences unique to the O-antigen biosynthesis cluster and flagellin of a given serovar. Serovar is assigned then to a Salmonella isolate based on the appearance of specific, size amplicons (PCR product) corresponding to the target allele.

Current commercial PCRs tests for identifying Salmonella target genes unique to this genus.  However, there are two species, six subspecies, and over ...

Characterization of Inflammatory Responses During Intranasal Colonization with Streptococcus pneumoniae

Nasopharyngeal colonization by Streptococcus pneumoniae is a prerequisite to invasion to the lungs or bloodstream1. This organism is capable of colonizing the mucosal surface of the nasopharynx, where it can reside, multiply and eventually overcome host defences to invade to other tissues of the host. Establishment of an infection in the normally lower respiratory tract results in pneumonia. Alternatively, the bacteria can disseminate into the bloodstream causing bacteraemia, which is associated with high mortality rates2, or else lead directly to the development of pneumococcal meningitis. Understanding the kinetics of, and immune responses to, nasopharyngeal colonization is an important aspect of S. pneumoniae infection models.
Our mouse model of intranasal colonization is adapted from human models3 and has been used by multiple research groups in the study of host-pathogen responses in the nasopharynx4-7. In the first part of the model, we use a clinical isolate of S. pneumoniae to establish a self-limiting bacterial colonization that is similar to carriage events in human adults. The procedure detailed herein involves preparation of a bacterial inoculum, followed by the establishment of a colonization event through delivery of the inoculum via an intranasal route of administration. Resident macrophages are the predominant cell type in the nasopharynx during the steady state. Typically, there are few lymphocytes present in uninfected mice8, however mucosal colonization will lead to low- to high-grade inflammation (depending on the virulence of the bacterial species and strain) that will result in an immune response and the subsequent recruitment of host immune cells. These cells can be isolated by a lavage of the tracheal contents through the nares, and correlated to the density of colonization bacteria to better understand the kinetics of the infection.

Characterization of Inflammatory Responses During Intranasal Colonization with Streptococcus pneumoniae

Colonization of the murine nasopharynx with Streptococcus pneumoniae and the subsequent extraction of adherent or recruited cells is described. This technique involves flushing the nasopharynx and collection of the fluid through the nares and is adaptable for various readouts, including differential cell quantification and analysis of mRNA expression in situ.

Nasopharyngeal colonization by Streptococcus pneumoniae is a prerequisite to invasion to the lungs or bloodstream1. This organism is capable of colonizing ...

Multiplex PCR Assay for Typing of Staphylococcal Cassette Chromosome Mec Types I to V in Methicillin-resistant Staphylococcus aureus

Staphylococcal Cassette Chromosome mec (SCCmec) typing is a very important molecular tool for understanding the epidemiology and clonal strain relatedness of methicillin-resistant Staphylococcus aureus (MRSA), particularly with the emerging outbreaks of community-associated MRSA (CA-MRSA) occurring on a worldwide basis. Traditional PCR typing schemes classify SCCmec by targeting and identifying the individual mec and ccr gene complex types, but require the use of many primer sets and multiple individual PCR experiments. We designed and published a simple multiplex PCR assay for quick-screening of major SCCmec types and subtypes I to V, and later updated it as new sequence information became available. This simple assay targets individual SCCmec types in a single reaction, is easy to interpret and has been extensively used worldwide. However, due to the sophisticated nature of the assay and the large number of primers present in the reaction, there is the potential for difficulties while adapting this assay to individual laboratories. To facilitate the process of establishing a MRSA SCCmec assay, here we demonstrate how to set up our multiplex PCR assay, and discuss some of the vital steps and procedural nuances that make it successful.

Multiplex PCR Assay for Typing of Staphylococcal Cassette Chromosome Mec Types I to V in Methicillin-resistant Staphylococcus aureus

We demonstrate a simple multiplex PCR assay for quick-screening and typing of Staphylococcal Cassette Chromosome mec (SCCmec) types I-V for methicillin-resistant Staphylococcus aureus, and provide some of the vital steps and procedural nuances that make it successful for adapting this assay to individual laboratories.

Staphylococcal Cassette Chromosome mec (SCCmec) typing  is a very important molecular tool for understanding the epidemiology and  clonal strain ...

Capsular Serotyping of Streptococcus pneumoniae by Latex Agglutination

Latex agglutination reagents are widely used in microbial diagnosis, identification and serotyping. Streptococcus pneumoniae (the pneumococcus) is a major cause of morbidity and mortality world-wide. Current vaccines target the pneumococcal capsule, and there are over 90 capsular serotypes. Serotyping pneumococcal isolates is therefore important for assessing the impact of vaccination programs and for epidemiological purposes. The World Health Organization has recommended latex agglutination as an alternative method to the &#8216;gold standard&#8217; Quellung test for serotyping pneumococci. Latex agglutination is a relatively simple, quick and inexpensive method; and is therefore suitable for resource-poor settings as well as laboratories with high-volume workloads. Latex agglutination reagents can be prepared in-house utilizing commercially-sourced antibodies that are passively attached to latex particles. This manuscript describes a method of production and quality control of latex agglutination reagents, and details a sequential testing approach which is time- and cost-effective. 
This method of production and quality control may also be suitable for other testing purposes.

Capsular Serotyping of Streptococcus pneumoniae by Latex Agglutination

Latex agglutination testing is a simple, rapid and inexpensive method for serotyping Streptococcus pneumoniae, and has also been widely applied in diagnostic microbiology. This manuscript describes the in-house production of latex agglutination reagents, quality control procedures and the application of this technique to pneumococcal serotyping.

Latex agglutination reagents are widely used in microbial diagnosis, identification and serotyping. Streptococcus pneumoniae (the pneumococcus) is a major ...

Using the Overlay Assay to Qualitatively Measure Bacterial Production of and Sensitivity to Pneumococcal Bacteriocins

Streptococcus pneumoniae colonizes the highly diverse polymicrobial community of the nasopharynx where it must compete with resident organisms. We have shown that bacterially produced antimicrobial peptides (bacteriocins) dictate the outcome of these competitive interactions. All fully-sequenced pneumococcal strains harbor a bacteriocin-like peptide (blp) locus. The blp locus encodes for a range of diverse bacteriocins and all of the highly conserved components needed for their regulation, processing, and secretion. The diversity of the bacteriocins found in the bacteriocin immunity region (BIR) of the locus is a major contributor of pneumococcal competition. Along with the bacteriocins, immunity genes are found in the BIR and are needed to protect the producer cell from the effects of its own bacteriocin. The overlay assay is a quick method for examining a large number of strains for competitive interactions mediated by bacteriocins. The overlay assay also allows for the characterization of bacteriocin-specific immunity, and detection of secreted quorum sensing peptides. The assay is performed by pre-inoculating an agar plate with a strain to be tested for bacteriocin production followed by application of a soft agar overlay containing a strain to be tested for bacteriocin sensitivity. A zone of clearance surrounding the stab indicates that the overlay strain is sensitive to the bacteriocins produced by the pre-inoculated strain. If no zone of clearance is observed, either the overlay strain is immune to the bacteriocins being produced or the pre-inoculated strain does not produce bacteriocins. To determine if the blp locus is functional in a given strain, the overlay assay can be adapted to evaluate for peptide pheromone secretion by the pre-inoculated strain. In this case, a series of four lacZ-reporter strains with different pheromone specificity are used in the overlay.

Competition in Streptococcus pneumoniae is mediated by bacteriocins, small antimicrobial peptides with inhibitory activity towards pneumococcus and other related species.&#160; Here we describe an optimized bacterial overlay assay that allows for the characterization of bacteriocin activity and inhibitory spectrum, bacteriocin-specific immunity, and detection of secreted quorum sensing peptides.

Streptococcus pneumoniae colonizes the highly diverse polymicrobial community of the nasopharynx where it must compete with resident organisms.  We have ...

Visualization of Streptococcus pneumoniae within Cardiac Microlesions and Subsequent Cardiac Remodeling

During bacteremia Streptococcus pneumoniae can translocate across the vascular endothelium into the myocardium and form discrete bacteria-filled microscopic lesions (microlesions) that are remarkable due to the absence of infiltrating immune cells. Due to their release of cardiotoxic products, S. pneumoniae within microlesions are thought to contribute to the heart failure that is frequently observed during fulminate invasive pneumococcal disease in adults. Herein is demonstrated a protocol for experimental mouse infection that leads to reproducible cardiac microlesion formation within 30 hr. Instruction is provided on microlesion identification in hematoxylin &#38; eosin stained heart sections and the morphological distinctions between early and late microlesions are highlighted. Instruction is provided on a protocol for verification of S. pneumoniae within microlesions using antibodies against pneumococcal capsular polysaccharide and immunofluorescent microscopy. Last, a protocol for antibiotic intervention that rescues infected mice and for the detection and assessment of scar formation in the hearts of convalescent mice is provided. Together, these protocols will facilitate the investigation of the molecular mechanisms underlying pneumococcal cardiac invasion, cardiomyocyte death, cardiac remodeling as a result of exposure to S. pneumoniae, and the immune response to the pneumococci in the heart.

Visualization of Streptococcus pneumoniae within Cardiac Microlesions and Subsequent Cardiac Remodeling

Streptococcus pneumoniae forms discrete non-purulent microscopic lesions in the heart. Outlined is the protocol for a murine model of cardiac microlesion formation. Instruction is provided on microlesion visualization using microscopy, discrimination between early and late microlesions, and methods to detect cardiac remodeling in hearts of convalescent animals.

During bacteremia Streptococcus pneumoniae can translocate across the vascular endothelium into the myocardium and form discrete bacteria-filled ...

Medicine

Multiplex PCR and Reverse Line Blot Hybridization Assay (mPCR/RLB)

Multiplex PCR/Reverse Line Blot Hybridization assay allows the detection of up to 43 molecular targets in 43 samples using one multiplex PCR reaction followed by probe hybridization on a nylon membrane, which is re-usable. Probes are 5' amine modified to allow fixation to the membrane. Primers are 5' biotin modified which allows detection of hybridized PCR products using streptavidin-peroxidase and a chemiluminescent substrate via photosensitive film. With low setup and consumable costs, this technique is inexpensive (approximately US$2 per sample), high throughput (multiple membranes can be processed simultaneously) and has a short turnaround time (approximately 10 hours). 
The technique can be utilized in a number of ways. Multiple probes can be designed to detect sequence variation within a single amplified product, or multiple products can be amplified
simultaneously, with one (or more) probes used for subsequent detection. A combination of both approaches can also be used within a single assay. The ability to include multiple probes for a single target sequence makes the assay highly specific.
Published applications of mPCR/RLB include detection of antibiotic resistance genes1,2, typing of methicillin-resistant Staphylococcus aureus3-5 and Salmonella sp6, molecular serotyping of Streptococcus pneumoniae7,8, Streptococcus agalactiae9 and enteroviruses10,11, identification of Mycobacterium sp12, detection of genital13-15 and respiratory tract16 and other17 pathogens and detection and identification of mollicutes18. However, the versatility of the technique means the applications are virtually limitless and not restricted to molecular analysis of micro-organisms.
The five steps in mPCR/RLB are a) Primer and Probe design, b) DNA extraction and PCR amplification c) Preparation of the membrane, d) Hybridization and detection, and e) Regeneration of the Membrane.

Multiplex PCR and Reverse Line Blot Hybridization Assay mPCR/RLB

An inexpensive, high throughput method for simultaneous detection of up to 43 molecular targets is described. Applications of mPCR/RLB include microbial typing and detection of multiple pathogens from clinical samples.

Multiplex PCR/Reverse Line Blot Hybridization assay allows the detection of up to 43 molecular targets in 43 samples using one multiplex PCR reaction ...

Biology

Homogeneous Glycoconjugate Produced by Combined Unnatural Amino Acid Incorporation and Click-Chemistry for Vaccine Purposes

Genetic code expansion is a powerful tool to introduce unnatural amino acids (UAAs) into proteins to modify their characteristics, to study or create new protein functions or to have access to protein conjugates. Stop codon suppression, in particular amber codon suppression, has emerged as the most popular method to genetically introduce UAAs at defined positions. This methodology is herein applied to the preparation of a carrier protein containing an UAA harboring a bioorthogonal functional group. This reactive handle can next be used to specifically and efficiently graft a synthetic oligosaccharide hapten to provide a homogeneous glycoconjugate vaccine. The protocol is limited to the synthesis of glycoconjugates in a 1:1 carbohydrate hapten/carrier protein ratio but amenable to numerous pairs of biorthogonal functional groups. Glycococonjugate vaccine homogeneity is an important criterion to ensure complete physico-chemical characterization, thereby, satisfying more and more demanding drug regulatory agency recommendations, a criterion which is unmet by classical conjugation strategies. Moreover, this protocol makes it possible to finely tune the structure of the actual conjugate vaccine, giving rise to tools to address structure-immunogenicity relationships.

Genetic code expansion is applied for the introduction of an unnatural amino acid bearing a biorthogonal functional group on a carrier protein at a defined site. The biorthogonal function is further used for the site-selective coupling of a carbohydrate antigen to provide a homogeneous glycoconjugate vaccine.

Genetic code expansion is a powerful tool to introduce unnatural amino acids (UAAs) into proteins to modify their characteristics, to study or create new ...

Bioengineering

Opsonophagocytic Killing Assay to Assess Immunological Responses Against Bacterial Pathogens

A key aspect of the immune response to bacterial colonization of the host is phagocytosis. An opsonophagocytic killing assay (OPKA) is an experimental procedure in which phagocytic cells are co-cultured with bacterial units. The immune cells will phagocytose and kill the bacterial cultures in a complement-dependent manner. The efficiency of the immune-mediated cell killing is dependent on a number of factors and can be used to determine how different bacterial cultures compare with regard to resistance to cell death. In this way, the efficacy of potential immune-based therapeutics can be assessed against specific bacterial strains and/or serotypes. In this protocol, we describe a simplified OPKA that utilizes basic culture conditions and cell counting to determine bacterial cell viability after co-culture with treatment conditions and HL-60 immune cells. This method has been successfully utilized with a number of different pneumococcal serotypes, capsular and acapsular strains, and other bacterial species. The advantages of this OPKA protocol are its simplicity, versatility (as this assay is not limited to antibody treatments as opsonins), and minimization of time and reagents to assess basic experimental groups.

This opsonophagocytic killing assay is used to compare the ability of phagocytic immune cells to respond to and kill bacteria based on different treatments and/or conditions. Classically, this assay serves as the gold&#160;standard for assessing effector functions of antibodies raised against a bacterium as opsonin.

A key aspect of the immune response to bacterial colonization of the host is phagocytosis. An opsonophagocytic killing assay (OPKA) is an experimental ...

Constructing Mutants in Serotype 1 Streptococcus pneumoniae strain 519/43

Streptococcus pneumoniae serotype 1 remains a huge problem in low-and-middle income countries, particularly in sub-Saharan Africa. Despite its importance, studies in this serotype have been hindered by the lack of genetic tools to modify it. In this study, we describe a method to genetically modify a serotype 1 clinical isolate (strain 519/43). Interestingly, this was achieved by exploiting the Pneumococcus&#8217; ability to naturally acquire DNA. However, unlike most pneumococci, the use of linear DNA was not successful; to mutate this important strain, a suicide plasmid had to be used. This methodology has provided the means for a deeper understanding of this elusive serotype, both in terms of its biology and pathogenicity. To validate the method, the major known pneumococcal toxin, pneumolysin, was mutated because it has a well-known and easy to follow phenotype. We showed that the mutant, as expected, lost its ability to lyse red blood cells. By being able to mutate an important gene in the serotype of interest, we were able to observe different phenotypes for loss of function mutants upon intraperitoneal and intranasal infections from the ones observed for other serotypes. In summary, this study proves that strain 519/43 (serotype 1) can be genetically modified.

Constructing Mutants in Serotype 1 Streptococcus pneumoniae strain 519/43

Here, we describe a S. pneumoniae serotype 1 strain 519/43 that can be genetically modified by using its ability to naturally acquire DNA and a suicide-plasmid. As proof of principle, an isogenic mutant in the pneumolysin (ply) gene was made.

Streptococcus pneumoniae serotype 1 remains a huge problem in low-and-middle income countries, particularly in sub-Saharan Africa. Despite its importance, ...

Capsular Serotyping of Streptococcus pneumoniae Using the Quellung Reaction

Summary

Explore More Videos

Chapters in this video

An Allelotyping PCR for Identifying Salmonella enterica serovars Enteritidis, Hadar, Heidelberg, and Typhimurium

Characterization of Inflammatory Responses During Intranasal Colonization with Streptococcus pneumoniae

Multiplex PCR Assay for Typing of Staphylococcal Cassette Chromosome Mec Types I to V in Methicillin-resistant Staphylococcus aureus

Capsular Serotyping of Streptococcus pneumoniae by Latex Agglutination

Using the Overlay Assay to Qualitatively Measure Bacterial Production of and Sensitivity to Pneumococcal Bacteriocins

Visualization of Streptococcus pneumoniae within Cardiac Microlesions and Subsequent Cardiac Remodeling

Multiplex PCR and Reverse Line Blot Hybridization Assay (mPCR/RLB)

Homogeneous Glycoconjugate Produced by Combined Unnatural Amino Acid Incorporation and Click-Chemistry for Vaccine Purposes

Opsonophagocytic Killing Assay to Assess Immunological Responses Against Bacterial Pathogens

Constructing Mutants in Serotype 1 Streptococcus pneumoniae strain 519/43