We thank William Rainey Harper College and the University of Illinois at Chicago for the facility to conduct these experiments. We also thank McGraw Hill Foundation for their generous support.

1. Medium Preparation
<ol>
	<li>Prepare 1 L of Tryptic Soy Broth (TSB): Into 1 L of distilled water, add 15 g of pancreatic digest of casein, 5 g of papaic digest of soybean meal, 3 g of sodium chloride, 2.5 g of dextrose, and 2.5 g of dipotassium phosphate. Sterilize before use.</li>
	<li>For Tryptic Soy Agar (TSA), add 15 g of agar to 1 L of TSB, autoclave. Then let it cool down to room temperature. Next, pour at a ratio of 20 mL per Petri dish (100 mm x 15 mm).</li>
	<li>Biofilm culture medium: Add 10 g of glucose to 1 L of autoclaved TSB. Sterilize by filtration using a 0.2 &#181;m filter.</li>
</ol>
2. S. aureus Biofilm Formation in 96 well Tissue Culture Plate
NOTE: The S. aureus biofilm is cultured as previously described6,21.
<ol>
	<li>Inoculate one individual colony of S. aureus from TSA in 10 mL of TSB and grow overnight at 37 &#176;C.</li>
	<li>Dilute the overnight culture into 10 mL of TSB/glucose (10 g/L) at a 1:100 (v/v) ratio. Vortex gently to mix for a consistent concentration.</li>
	<li>Transfer 200 &#956;L of diluted culture into a total of 18 wells (more for experimental groups, such a non-biofilm control to suggest a relationship to ALP activity6) from one 96 well plate. Use triplets for each time point: 0 min, 15 min, 30 min, 45 min, 60 min, and 75 min. See step 3.2.</li>
	<li>Incubate the 96 well plate at 37 &#176;C for 24 h for biofilm formation6,21.</li>
	<li>Decant the supernatant by aspiration.</li>
	<li>Wash each well with 1x phosphate buffered solution (PBS, pH 7.4), centrifuge for 5 min at 15,000 x g and decant the supernatant by aspiration.</li>
</ol>
3. Measurement of ALP Activity in S. aureus Biofilm
NOTE: ALP activity was measured as described6,18.
<ol>
	<li>Add 75 &#956;L of buffered ALP substrate consisting of commercially available pNPP to each well from step 2.6 and begin recording the time. Record each time point in triplicate.</li>
	<li>After incubation for a varied time: 0 min (control), 15 min, 30 min, 45 min, 60 min, and 75 min respectively, add 75 &#181;L of 5 M NaOH to stop the reaction.</li>
	<li>Centrifuge the plate for 5 min at 15,000 x g.</li>
	<li>Transfer 100 &#181;L of supernatant into a new 96 well plate for colorimetric measurement.</li>
	<li>Measure the absorbance of each well at 405 nm using a 96 well plate reader. Use the 0 min time point wells to control for 405 nm background noise.</li>
	<li>Repeat the entire experiment in three individual 96 well plates.</li>
</ol>

<ol>
	<li>Coleman, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Structure+and+mechanism+of+alkaline+phosphatase.">Structure and mechanism of alkaline phosphatase.</a> Annual Review of Biophysics and Biomolecular Structure. 21, 441-483 (1992).</li><li>Sharma, U., Pal, D., Prasad, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Alkaline+Phosphatase:+An+Overview.">Alkaline Phosphatase: An Overview.</a> Indian Journal of Clinical Biochemistry. 29 (3), 269-278 (2014).</li><li>Mitchell, M. S., 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=High+frequencies+of+elevated+alkaline+phosphatase+activity+and+rickets+exist+in+extremely+low+birth+weight+infants+despite+current+nutritional+support.">High frequencies of elevated alkaline phosphatase activity and rickets exist in extremely low birth weight infants despite current nutritional support.</a> Boston Medical Center Pediatrics. 9, 47 (2009).</li><li>Fawley, J., Gourlay, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Intestinal+alkaline+phosphatase:+A+summary+of+its+role+in+clinical+disease.">Intestinal alkaline phosphatase: A summary of its role in clinical disease.</a> Journal of Surgical Research. 202 (1), 225-234 (2016).</li><li>Derman, A. I., Beckwith, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Escherichia+coli+Alkaline+Phosphatase+Localized+to+the+Cytoplasm+Slowly+Acquires+Enzymatic+Activity+in+Cells+Whose+Growth+Has+Been+Suspended:+a+Caution+for+Gene+Fusion+Studies.">Escherichia coli Alkaline Phosphatase Localized to the Cytoplasm Slowly Acquires Enzymatic Activity in Cells Whose Growth Has Been Suspended: a Caution for Gene Fusion Studies.</a> Journal of Bacteriology. 177 (13), 3764-3770 (1995).</li><li>Danikowski, K. M., Cheng, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Alkaline+Phosphatase+Activity+of+Staphylococcus+aureus+grown+in+Biofilm+and+Suspension+Cultures.">Alkaline Phosphatase Activity of Staphylococcus aureus grown in Biofilm and Suspension Cultures.</a> Current Microbiology. 75, 1226-1230 (2018).</li><li>Okabayashi, K., Futai, M., Mizuno, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Localization+of+Acid+and+Alkaline+Phosphatases+in+Staphylococcus+aureus.">Localization of Acid and Alkaline Phosphatases in Staphylococcus aureus.</a> Japanese Journal of Microbiology. 18 (4), 287-294 (1974).</li><li>Cheng, K. J., Costerton, J. 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H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+use+of+bacterial+alkaline+phosphatase+assay+for+rapid+monitoring+of+bacterial+counts+on+spinach.">The use of bacterial alkaline phosphatase assay for rapid monitoring of bacterial counts on spinach.</a> Journal of Food Science. 73 (5), M236-M238 (2008).</li><li>Barber, M., Kuper, S. W. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Identification+of+Staphylococcus+pyogenes+by+the+phosphatase+reaction.">Identification of Staphylococcus pyogenes by the phosphatase reaction.</a> The Journal of Pathology and Bacteriology. 63, 65-68 (1951).</li><li>Wolf, P. L., Von der Muehll, E., Ludwick, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+new+test+to+differentiate+Serratia+from+Enterobacter.">A new test to differentiate Serratia from Enterobacter.</a> American Journal of Clinical Pathology. 56, 241-243 (1972).</li><li>Rangam, C. M., Katdare, S. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Phosphatase+activity+of+Staphylococci+as+an+indication+of+their+pathogenicity.">Phosphatase activity of Staphylococci as an indication of their pathogenicity.</a> Indian Journal of Medical Science. 8, 610-613 (1954).</li><li>Flemming, H. -. 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=Biofilms:+an+emergent+form+of+bacterial+life.">Biofilms: an emergent form of bacterial life.</a> Nature Reviews Microbiology. 14, 563-575 (2016).</li><li>Hoiby, N., Bjarnsholt, T., Givskov, M., Molin, S., Ciofu, O. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Antibiotic+resistance+of+bacterial+biofilms.">Antibiotic resistance of bacterial biofilms.</a> International Journal of Antimicrobial Agents. 35, 322-332 (2010).</li><li>Ito, A., Taniuchi, A., May, T., Kawata, K., Okabe, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Increased+antibiotic+resistance+of+Escherichia+coli+in+mature+biofilms.">Increased antibiotic resistance of Escherichia coli in mature biofilms.</a> Applied and Environmental Microbiology. 75, 4093-4100 (2009).</li><li>Witherow, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+Ten-Week+Biochemistry+Lab+Project+Studying+Wild-Type+and+Mutant+Bacterial+Alkaline+Phosphatase.">A Ten-Week Biochemistry Lab Project Studying Wild-Type and Mutant Bacterial Alkaline Phosphatase.</a> Biochemistry and Molecular Biology Education. 44 (6), (2016).</li><li>Henthorn, P., Zervos, P., Raducha, M., Harris, H., Kadesch, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Expression+of+a+human+placental+alkaline+phosphatase+gene+in+transfected+cells:+Use+as+a+reporter+for+studies+of+gene+expression.">Expression of a human placental alkaline phosphatase gene in transfected cells: Use as a reporter for studies of gene expression.</a> Proceedings of the National Academy of Science USA. 85, 6324-6346 (1988).</li><li>Horney, B. S., Farmer, A. J., Honor, D. J., MacKenzie, A., Burton, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Agarose+gel+electrophoresis+of+alkaline+phosphatase+isoenzymes+in+the+serum+of+hyperthyroid+cats.">Agarose gel electrophoresis of alkaline phosphatase isoenzymes in the serum of hyperthyroid cats.</a> Veterinary Clinical Pathology. 23 (3), 98-102 (1994).</li><li>Farley, J. R., 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=Quantification+of+Skeletal+Alkaline+Phosphatase+in+Osteoporotic+Serum+by+Wheat+Germ+Agglutinin+Precipitation,+Heat+Inactivation,+and+a+Two-Site+Immunoradiometric+Assay.">Quantification of Skeletal Alkaline Phosphatase in Osteoporotic Serum by Wheat Germ Agglutinin Precipitation, Heat Inactivation, and a Two-Site Immunoradiometric Assay.</a> Clinical Chemistry. 40 (9), 1749-1756 (1994).</li><li>O&#8217;Toole, G. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Microtiter+Dish+Biofilm+Formation+Assay.">Microtiter Dish Biofilm Formation Assay.</a> Journal of Visualized Experience. , (2011).</li><li>Nomoto, M., Ohsawa, M., Wang, H. L., Chen, C. C., Yeh, K. 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The authors have nothing to disclose.

In our assay, we used pNPP as the ALP substrate. This is a working solution designed for ELISA and no dilution is needed. After hydrolysis by ALP, a yellow product develops and can be measured at 405 nm. At the end of the enzymatic reaction, we briefly centrifuged the 96 well plate and transferred the supernatant to a fresh 96 well plate to measure absorbance using the plate reader. We found that this extra centrifugation step is critical, since it increases the consistency of absorbance at 405 nm, probably by eliminating any possible suspended cells incurred during enzymatic reaction.
For biofilm formation, we use 200 &#956;L of a 1:100 (v/v) dilution for overnight culture as reported6,21. This is the optimum dilution for S. aureus to form biofilm compared to other dilutions (data not shown). Since the purpose of this paper is to measure ALP activity in biofilm, it was crucial that we maintained optimum biofilm culture conditions. This was further emphasized by the choice in using glucose at 10 g/L for optimum biofilm growth6. The dilution factor and glucose concentration need to be optimized if different bacterial cells are used for biofilm formation.
During incubation of the biofilm culture with pNPP substrate, it will take time for the colored product to develop. We measured ALP activity after 15&#160;and 30 min time points which is when the visible yellow color is observed. With the current concentration, we noticed an increased ALP activity for up to 75 min as indicated in Figure 1. After 75 min, no increase of the ALP activity was observed.
Finally, since ALP in S. aureus is an exclusively membrane bound protein7, its activity can be tested without cell lysis. There are benefits to an enzyme activity assay that does not require whole cell destruction. Notably, the protein isolation process can sometimes yield a lower active enzyme quantity22. However, this protocol cannot be used if ALP is not in its membrane bound form.
As previously reported6, ALP activity is elevated in biofilm culture as compared to its platonic counterpart. The experimental settings used in the current study can be extended to investigate factors/compounds that affect ALP activity in S. aureus biofilm. The findings from these studies will provide additional insight into how to control bacterial biofilm formation.

Alkaline phosphatase (ALP) is ubiquitously expressed in both prokaryotic and eukaryotic cells1. It can catalyze the hydrolysis of monophosphate from different molecules such as nucleotides, proteins, alkaloids, phosphate esters and anhydrides of phosphoric acid. In humans, eukaryotic ALP is present in many tissues including liver, bone, intestine and placenta2. It plays important roles in protein phosphorylation, cell growth, apoptosis, stem cell processes as well as normal skeletal mineralization. Eukaryotic ALP is also a key serum indicator for the presence of diseases in bone, liver, and other tissues/organs when elevated3,4.
Prokaryotic ALP has been detected in a variety of bacterial cells, including E. coli5, S. aureus6,7 and some common rumen bacteria in the soils8. Bacterial ALP activity has been used as a biosensor in the detection of pesticides, heavy metals9 and bacterial contamination10. The constitutive expression of ALP has been used to identify Staphylococci11 and to differentiate Serratia from Enterobacter12. It is further suggested that constitutive ALP production is correlated with pathogenicity in staphylococci13. Although ALP has been studied in different settings3,4, yet little is reported for its activity and function in biofilms cultures.
A biofilm has been documented to have a differently functioning bacterial life as compared with its free-living bacterial cell counterpart14. In S. aureus, the formation of biofilm has been identified in a variety of clinical conditions and accounts for the antibiotic resistance and chronic inflammation15,16. Many molecules had been reported to be found in a biofilm matrix such as polysaccharides, proteins, nucleic acids, and lipids, but the mechanism of biofilm formation is not fully understood14. To understand the role of ALP in biofilm formation, we cultured S. aureus biofilms in 96 well tissue culture plates and measured the ALP activity using para-nitrophenylphosphate (pNPP).
The molecule pNPP is a ready-to-use substrate for ALP and has been widely used to measure ALP activity6,17,18. This colorimetric assay is based on the conversion of para-nitrophenyl phosphate (pNPP) to para-nitrophenol resulting in a colored product at 405 nm. Compared to other conventional ALP assay, such as agarose gel electrophoresis19, wheat germ agglutinin (WGA) precipitation, and WGA-HPLC20, this assay is highly specific, sensitive, easy to reproduce, and most importantly, allows for high throughput.

<table><tbody><tr><td>Agar</td><td>VWR</td><td>9002-18-0</td><td></td></tr><tr><td>Eppendorf Centrifuge</td><td>Thomas Scientific</td><td>5810</td><td></td></tr><tr><td>Gluose</td><td>VWR</td><td>50-99-7</td><td></td></tr><tr><td>NaOH pellets</td><td>VWR</td><td>SS0550-500GR</td><td></td></tr><tr><td>Para-nitrophenylphosphate (pNPP)&amp;nbsp;</td><td>Sigma</td><td>P7998-100ML</td><td>Typical concentrations of pNPP liquid substrates, often used in enzyme-linked immunesorbent assays (ELISA), range between 10 to 50 mM. Similar to most ready-to-use pNPP liquid substrates like the one used here, the exact pNPP concentration is not disclosed due to its proprietary nature.</td></tr><tr><td>10x PBS, pH7.4.&lt;br/&gt; 173 mM NaCl,&lt;br/&gt; 2.7 mM KCl,&lt;br/&gt; 8 mM Na&lt;sub&gt;2&lt;/sub&gt;HPO&lt;sub&gt;4&lt;/sub&gt;,&lt;br/&gt; 2 mM KH&lt;sub&gt;2&lt;/sub&gt;PO&lt;sub&gt;4&lt;/sub&gt;</td><td>Sigma</td><td>P3288-1VL</td><td></td></tr><tr><td>Plate Reader</td><td>Biotek</td><td>ELx808</td><td></td></tr><tr><td>&lt;em&gt;S. aureus&lt;/em&gt;</td><td>ATCC</td><td>ATCC25923</td><td></td></tr><tr><td>Tryptic Soy Agar&amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp; 15 g/L TSB</td><td>VWR</td><td>9002-18-0</td><td></td></tr><tr><td>Tryptic Soy Broth:&amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp; g/L&lt;br/&gt; Pancreatic Digest of Casein............ 15.0&lt;br/&gt; Papaic Digest of Soyben Meal.........5.00&lt;br/&gt; Sodium chloride.............................. 3.00&lt;br/&gt; Dextrose........................................&amp;nbsp; 2.50&lt;br/&gt; Dipotassium phosphate..................2.50</td><td>VWR</td><td>90006-098</td><td></td></tr><tr><td>96 well tissue culture plates</td><td>BD</td><td>6902D09</td><td>U shaped bottom</td></tr></tbody></table>

colorimetric analysis of alkaline phosphatase activity in s. aureus biofilm

Alkaline phosphatase (ALP) is a common enzyme expressed in both prokaryotic and eukaryotic cells. It catalyzes the hydrolysis of phosphate monoesters from many molecules at basic pH and plays an indispensable role in phosphate metabolism. In humans, eukaryotic ALP is one of the most frequently used enzymatic signals in diagnosing various diseases, such as cholestasis and rickets. In S. aureus, ALP is detected exclusively on the cell membrane; it is also expressed as a secretory form as well. Yet, little is known about its function in biofilm formation.
The purpose of this manuscript is to develop a quick and reliable assay to measure ALP activity in S. aureus biofilm that does not require protein isolation. Using p-nitrophenyl phosphate (pNPP) as a substrate, we measured ALP activity in S. aureus biofilm formed in 96-well tissue culture plates. Activity was based on the formation of the soluble reaction product measured by 405 nm absorbance. The high throughput nature of the 96 well tissue culture plate method provides a sensitive and reproducible method for ALP activity assays. The same experimental set up can also be extended to measure other extracellular molecular markers related to biofilm formation.

Figure 1 shows a representative result of ALP activity from biofilm cultures of S. aureus in 96 well tissue culture plates. 75 &#956;L of commercially available pNPP solution was added to each well and incubated at room temperature. After incubation for different times (0 min, 15 min, 30 min, 45 min, 60 min, and 75 min, respectively) 75 &#956;L of 5 M NaOH was added to stop the reaction. The product was then measured in a 96 well plate reader at 405 nm. Each time point was repeated in triplets from a single 96 well plate, and the entire experiment was repeated in 3 individual 96 well plates.
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/59285/59285fig1.jpg" /> 
Figure 1: S. aureus biofilm cultures were incubated with pNPP substrate for different time (0 min, 15 min, 30 min, 45 min, 60 min and 75 min) and their ALP activity was measured at 405 nm. Error bars represent standard deviation. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/59285/59285fig1large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>

Watch this Scientific Journal Video about Colorimetric Analysis of Alkaline Phosphatase Activity in S. aureus Biofilm at JoVE.com

Colorimetric Analysis of Alkaline Phosphatase Activity in S. aureus Biofilm

In this manuscript, we established a high throughput method to quantify alkaline phosphatase activity in S. aureus biofilm culture from 96-well tissue culture plate

Colorimetric Analysis of Alkaline Phosphatase Activity in S. aureus Biofilm

Alkaline phosphatase (ALP) is a common enzyme expressed in both prokaryotic and eukaryotic cells. It catalyzes the hydrolysis of phosphate monoesters from ...

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15.4K Views.  Harper College. In this manuscript, we established a high throughput method to quantify alkaline phosphatase activity in S. aureus biofilm culture from 96-well tissue culture plate

Video: Colorimetric Analysis of Alkaline Phosphatase Activity in S. aureus Biofilm

Anti-virulent Disruption of Pathogenic Biofilms using Engineered Quorum-quenching Lactonases

The rapid emergence of multi-drug resistant bacteria has accelerated the need for novel therapeutic approaches to counter life-threatening infections. The persistence of bacterial infection is often associated with quorum-sensing-mediated biofilm formation. Thus, the disruption of this signaling circuit presents an attractive anti-virulence strategy. Quorum-quenching lactonases have been reported to be effective disrupters of quorum-sensing circuits. However, there have been very few reports of the effective use of these enzymes in disrupting bacterial biofilm formation. This protocol describes a method to disrupt biofilm formation in a clinically relevant A. baumannii S1 strain through the use of an engineered quorum-quenching lactonase. Acinetobacter baumannii is a major human pathogen implicated in serious hospital-acquired infections globally and its virulence is attributed predominantly to its biofilm's tenacity. The engineered lactonase treatment achieved significant A. baumannii S1 biofilm reduction. This study also showed the possibility of using engineered quorum-quenching enzymes in future treatment of biofilm-mediated bacterial diseases. Lastly, the method may be used to evaluate the competency of promising quorum-quenching enzymes.

Quorum-quenching enzymes are anti-virulent and anti-bacterial options that can mitigate pathogenesis without risk of incurring resistance, by preventing the expression of virulence factors and genes associated with antibiotic resistance and biofilm formation. In this study, we report a method that demonstrates the efficacy of quorum-quenching enzymes in bacterial biofilm disruption.

The rapid emergence of multi-drug resistant bacteria has accelerated the need for novel therapeutic approaches to counter life-threatening infections. The ...

Immunology and Infection

Targeting Biofilm Associated Staphylococcus aureus Using Resazurin Based Drug-susceptibility Assay

Most pathogenic bacteria are able to form biofilms during infection, but due to the difficulty of manipulating and assessing biofilms, the vast majority of laboratory work is conducted with planktonic cells. Here, we describe a peg plate biofilm assay as performed with Staphylococcus aureus. Bacterial biofilms are grown on pegs attached to a 96-well microtiter plate lid, washed through gentle submersion in buffer, and placed in a drug challenge plate. After subsequent incubation they are again washed and moved to a final recovery plate, in which the fluorescent dye resazurin serves as a viability indicator. This assay offers greatly increased ease-of-use, reliability, and reproducibility, as well as a wealth of data when conducted as a kinetic read. Moreover, this assay can be adapted to a medium-throughput drug screening approach by which an endpoint fluorescent readout is taken instead, offering a path for drug discovery efforts.

Targeting Biofilm Associated Staphylococcus aureus Using Resazurin Based Drug-susceptibility Assay

Most bacterial infections produce a biofilm. By virtue of their environment, biofilm associated bacteria are often phenotypically drug resistant. Novel antibacterial molecules that kill bacteria in biofilms are thus a high priority. We establish an assay to quickly screen for antimicrobial compounds that are effective at eradicating biofilms.

Most pathogenic bacteria are able to form biofilms during infection, but due to the difficulty of manipulating and assessing biofilms, the vast majority ...

A Platform of Anti-biofilm Assays Suited to the Exploration of Natural Compound Libraries

Biofilms are regarded as one of the most challenging topics of modern biomedicine, and they are potentially responsible for over 80% of antibiotic-tolerant infections. Biofilms have displayed an exceptionally high tolerance for chemotherapy, which is thought to be multifactorial. For instance, the matrix provides a physical barrier that decreases the penetration of antibiotics into the biofilm. Also, cells within the biofilms are phenotypically diverse. Likely, biofilm resilience arises from a combination of these and other, yet unknown, mechanisms. All of the currently existing antibiotics have been developed against single-cells (planktonic) bacteria. Therefore, so far, a very limited repertoire of molecules exists that can selectively act on mature biofilms. This situation has driven a progressive paradigm shift in drug discovery, in which searching for anti-biofilms has been urged to occupy a more prominent place. An additional challenge is that there are a very limited number of standardized methods for biofilm research, especially those that can be used for large-throughput screening of chemical libraries. Here, an experimental anti-biofilm platform for chemical screening is presented. It uses three assays to measure biofilm viability (with resazurin staining), total biomass (with crystal violet staining), and biofilm matrix (using a wheat germ agglutinin, WGA-fluorescence-based staining of the poly-N-acetyl-glucosamine, PNAG, fraction). All the assays were developed using Staphylococcus aureus as the model bacteria. Examples of how the platform can be used for primary screening as well as for functional characterization of identified anti-biofilm hits are presented. This experimental sequence further allows for the classification of the hits based upon the measured end-points. It also provides information on their mode of action, especially on long-term versus short-term chemotherapeutic effects. Thus, it is very advantageous for the quick identification of high-quality hit compounds that can serve as starting points for various biomedical applications.

Biofilm infections show high tolerance towards chemotherapy. No single assay captures the complexity of biofilms. Instead, complementary assays are needed. We present a screening platform (developed for S. aureus) that combines assays for viability, biomass, and biofilm matrix. It allows anti-biofilm drug discovery, including the assessment of long-term chemotherapeutic effects.

Biofilms are regarded as one of the most challenging topics of modern biomedicine, and they are potentially responsible for over 80% of ...

Monitoring Extracellular pH in Cross-Kingdom Biofilms using Confocal Microscopy

Cross-kingdom biofilms consisting of both fungal and bacterial cells are involved in a variety of oral diseases, such as endodontic infections, periodontitis, mucosal infections and, most notably, early childhood caries. In all of these conditions, the pH in the biofilm matrix impacts microbe-host interactions and thus the disease progression. The present protocol describes a confocal microscopy-based method to monitor pH dynamics inside cross-kingdom biofilms comprising Candida albicans and Streptococcus mutans. The pH-dependent dual-emission spectrum and the staining properties of the ratiometric probe C-SNARF-4 are exploited to determine drops in pH in extracellular areas of the biofilms. Use of pH ratiometry with the probe requires a meticulous choice of imaging parameters, a thorough calibration of the dye, and careful, threshold-based post-processing of the image data. When used correctly, the technique allows for the rapid assessment of extracellular pH in different areas of a biofilm and thus the monitoring of both horizontal and vertical pH gradients over time. While the use of confocal microscopy limits Z-profiling to thin biofilms of 75 &#181;m or less, the use of pH ratiometry is ideally suited for the noninvasive study of an important virulence factor in cross-kingdom biofilms.

The protocol describes the cultivation of cross-kingdom biofilms consisting of Candida albicans and Streptococcus mutans and presents a confocal microscopy-based method for the monitoring of extracellular pH inside these biofilms.

Cross-kingdom biofilms consisting of both fungal and bacterial cells are involved in a variety of oral diseases, such as endodontic infections, ...

Standardized In vitro Assays to Visualize and Quantify Interactions between Human Neutrophils and Staphylococcus aureus Biofilms

Neutrophils are the first line of defense deployed by the immune system during microbial infection. In vivo, neutrophils are recruited to the site of infection where they use processes such as phagocytosis, production of reactive oxygen and nitrogen species (ROS, RNS, respectively), NETosis (neutrophil extracellular trap), and degranulation to kill microbes and resolve the infection. Interactions between neutrophils and planktonic microbes have been extensively studied. There have been emerging interests in studying infections caused by biofilms in recent years. Biofilms exhibit properties, including tolerance to killing by neutrophils, distinct from their planktonic-grown counterparts. With the successful establishment of both in vitro and in vivo biofilm models, interactions between these microbial communities with different immune cells can now be investigated. Here, techniques that use a combination of traditional biofilm models and well-established neutrophil activity assays are tailored specifically to study neutrophil and biofilm interactions. Wide-field fluorescence microscopy is used to monitor the localization of neutrophils in biofilms. These biofilms are grown in static conditions, followed by the addition of neutrophils derived from human peripheral blood. The samples are stained with appropriate dyes prior to visualization under the microscope. Additionally, the production of ROS, which is one of the many neutrophil responses against pathogens, is quantified in the presence of a biofilm. The addition of immune cells to this established system will expand the understanding of host-pathogen interactions while ensuring the use of standardized and optimized conditions to measure these processes accurately.

Standardized In vitro Assays to Visualize and Quantify Interactions between Human Neutrophils and Staphylococcus aureus Biofilms

The present protocol describes the study of neutrophil-biofilm interactions. Staphylococcus aureus biofilms are established in vitro and incubated with peripheral blood-derived human neutrophils. The oxidative burst response from neutrophils is quantified, and the neutrophil localization within the biofilm is determined by microscopy.

Neutrophils are the first line of defense deployed by the immune system during microbial infection. In vivo, neutrophils are recruited to the site of ...

An In Vitro Model to Study the Effect of 5-Aminolevulinic Acid-mediated Photodynamic Therapy on Staphylococcus aureus Biofilm

Staphylococcus aureus (S. aureus) is a common human pathogen, which causes pyogenic and systemic infections. S. aureus infections are difficult to eradicate not only due to the emergence of antibiotic-resistant strains but also its ability to form biofilms. Recently, photodynamic therapy (PDT) has been indicated as one of the potential treatments for controlling biofilm infections. However, further studies are required to improve our knowledge of its effect on bacterial biofilms, as well as the underlying mechanisms. This manuscript describes an in vitro model of PDT with 5-aminolevulinic acid (5-ALA), a precursor of the actual photosensitizer, protoporphyrin IX (PpIX). Briefly, mature S. aureus biofilms were incubated with ALA and then exposed to light. Subsequently, the antibacterial effect of ALA-PDT on S. aureus biofilm was quantified by calculating the colony forming units (CFUs) and visualized by viability fluorescent staining via confocal laser scanning microscopy (CLSM). Representative results demonstrated a strong antibacterial effect of ALA-PDT on S. aureus biofilms. This protocol is simple and can be used to develop an in vitro model to study the treatment of S. aureus biofilms with ALA-PDT. In the future, it could also be referenced in PDT studies utilizing other photosensitizers for different bacterial strains with minimal adjustments.

An In Vitro Model to Study the Effect of 5-Aminolevulinic Acid-mediated Photodynamic Therapy on Staphylococcus aureus Biofilm

This manuscript describes a protocol to study the antimicrobial effect of 5-aminolevulinic acid-mediated photodynamic therapy (ALA-PDT) on a Staphylococcus aureus biofilm. This protocol can be used to develop an in vitro model to study the treatment of bacterial biofilms with PDT in the future.

Staphylococcus aureus (S. aureus) is a common human pathogen, which causes pyogenic and systemic infections. S. aureus infections are difficult to ...

Biology

Direct Detection of Isolevuglandins in Tissues Using a D11 scFv-Alkaline Phosphatase Fusion Protein and Immunofluorescence

Isolevuglandins (IsoLGs) are highly reactive gamma ketoaldehydes formed from H2-isoprostanes through lipid peroxidation and crosslink proteins leading to inflammation and various diseases including hypertension. Detection of IsoLG accumulation in tissues is crucial in shedding light on their involvement in the disease processes. However, measurement of IsoLGs in tissues is extremely difficult, and currently available tools, including mass spectrometry analysis, are laborious and extremely expensive. Here we describe a novel method for in situ detection of IsoLGs in tissues using alkaline phosphatase-conjugated D11 ScFv and a recombinant phage-display antibody produced in E. coli by immunofluorescent microscopy. Four controls were used for validating the staining: (1) staining with and without D11, (2) staining with bacterial periplasmic extract with the alkaline phosphatase linker, (3) irrelevant scFV antibody staining, and (4) competitive control with IsoLG prior to the staining. We demonstrate the effectiveness of the alkaline phosphatase-conjugated D11 in both human and mouse tissues with or without hypertension. This method will likely serve as an important tool to study the role of IsoLGs in a wide variety of disease processes.

This article provides a detailed methodology for the measurement of isolevuglandins in tissues by immunofluorescence using alkaline phosphatase-conjugated ScFv D11 antibody. Hypertension models in both mice and humans are used to explain the step-by-step procedures and fundamental principles associated with isolevuglandin measurement in tissue samples.

Isolevuglandins (IsoLGs) are highly reactive gamma ketoaldehydes formed from H2-isoprostanes through lipid peroxidation and crosslink proteins leading to ...

Determination of ROS Production by Neutrophils upon Interaction with Opsonized Biofilm

Source: Rana, P. S. J. B., et al. <a href="https://app-jove-com.remotexs.ntu.edu.sg/v/63773">Standardized In vitro Assays to Visualize and Quantify Interactions between Human Neutrophils and Staphylococcus aureus Biofilms.</a> J. Vis. Exp. (2022)
In this video, we demonstrate an in vitro chemiluminescence assay to detect the generation of reactive oxygen species by neutrophils upon exposure to an opsonized bacterial biofilm.

Oznaczanie produkcji ROS przez neutrofile po interakcji z opsonizowanym biofilmem

Source: Rana, P. S. J. B., et al. Standardized In vitro Assays to Visualize and Quantify Interactions between Human Neutrophils and Staphylococcus aureus ...

JoVE Encyclopedia of Experiments

Immunology

Immune Response

Host Defense Mechanism

An In Vitro Assay to Study the Interaction between Neutrophils and Biofilm

Source: Rana, P. S. J. B., et al. <a href="https://app-jove-com.remotexs.ntu.edu.sg/v/63773">Standardized In vitro Assays to Visualize and Quantify Interactions between Human Neutrophils and Staphylococcus aureus Biofilms.</a> J. Vis. Exp. (2022)
This video demonstrates an in vitro assay to study neutrophil-biofilm interaction. The pathogenic bacteria embedded in the biofilm and isolated neutrophils were tagged using fluorescent labels, and the immune response by the neutrophils and the evasion of the immune response by the bacteria were assessed using a fluorescence microscope.

Test in vitro do badania interakcji między neutrofilami a biofilmem

A Peg Plate Biofilm Assay for Screening Antibacterial Agents

Source: Dalecki, A. G., et al. <a href="https://app-jove-com.remotexs.ntu.edu.sg/v/53925">Targeting Biofilm Associated Staphylococcus aureus Using Resazurin Based Drug-susceptibility Assay.</a> J. Vis. Exp. (2016)
This video demonstrates an assay for screening antimicrobial compounds that efficiently eliminate biofilms using a peg-plate. The methodology monitors the biofilm&#39;s metabolic state after treatment with antimicrobial compounds, facilitating the determination of the minimum biofilm eradication concentration.

Test biofilmu na płytce kołkowej do badań przesiewowych środków przeciwbakteryjnych

1. Biofilm Initiation

	Grow a culture of biofilm-producing organisms in a nutrient-rich medium. Inoculate&#160;Staphylococcus aureus&#160;strain Newman ...

Colorimetric Analysis of Alkaline Phosphatase Activity in S. aureus Biofilm

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Anti-virulent Disruption of Pathogenic Biofilms using Engineered Quorum-quenching Lactonases

Targeting Biofilm Associated Staphylococcus aureus Using Resazurin Based Drug-susceptibility Assay

A Platform of Anti-biofilm Assays Suited to the Exploration of Natural Compound Libraries

Monitoring Extracellular pH in Cross-Kingdom Biofilms using Confocal Microscopy

Standardized In vitro Assays to Visualize and Quantify Interactions between Human Neutrophils and Staphylococcus aureus Biofilms

An In Vitro Model to Study the Effect of 5-Aminolevulinic Acid-mediated Photodynamic Therapy on Staphylococcus aureus Biofilm

Direct Detection of Isolevuglandins in Tissues Using a D11 scFv-Alkaline Phosphatase Fusion Protein and Immunofluorescence

Oznaczanie produkcji ROS przez neutrofile po interakcji z opsonizowanym biofilmem

Test in vitro do badania interakcji między neutrofilami a biofilmem

Test biofilmu na płytce kołkowej do badań przesiewowych środków przeciwbakteryjnych