Congo Red Agar Test Research Articles

Biofilm generation and antibiotic resistant profile of extensive and multidrug resistant Pseudomonas aeruginosa from burn patients in Ahvaz: A cross-sectional study.

Multidrug and extensive drug-resistant Pseudomonas aeruginosa was extracted from burn patients referring to burn centers in southwest Iran so that biofilm generation and antibiotic resistance could be investigated. A specific primer was used to confirm all our considered 110 P. aeruginosa culture-positive reports on 345 burn patients. The resistance of P. aeruginosa to seven antibiotics and Colistin with minimum inhibitory concentration (MIC) was assessed. Biofilm formation was assessed by the phenotypic study of specimens under Congo red agar and microtiter plate assays. One hundred and 10 clinical P. aeruginosa isolates taken from burn wound infections were validated. Among P. aeruginosa isolates, Piperacillin, Ceftazidime, Maeropenem, Gentamycin, and Gatifloacin had the highest resistance to antibiotics, while Ticarcillin-Clavulanic acid and Ceftolozane-Tazobactam showed the least resistance. MICs were then evaluated via the E test. Seven isolates were resistant to colistin. Colistin reference MICs for multidrug-resistant P. aeruginosa prevalence was 38%, while it was 22% for extensively drug-resistant (XDR) P. aeruginosa. One P. aeruginosa was pandrug-resistant (PDR). Under Congo red agar test, 66 isolates (67%) formed biofilms and black colonies, whereas 44 isolates (50%) had red colonies. In MTP, 76% formed biofilm. 40%, 32%, 21% of the isolates were strong, moderate, and weak biofilm formers, respectively, while 43% did not form biofilms. The P. aeruginosa resistance to antimicrobial agents has largely challenged the control of the infection. Accordingly, a higher resistance occurred when the isolates were transferred to the patients. Less than 50% P. aeruginosa samples generated strong biofilms. Consequently, hygienic measurements are essential to inhibit P. aeruginosa transmission to hospitalized patients.

Bioactive exopolysaccharide from Limosilactobacillus fermentum LAB-1: Antioxidant, anti-inflammatory, antibacterial and antibiofilm properties

Exopolysaccharides (EPS) are an intriguing group of high-molecular-weight carbohydrate polymers known for their diverse functional benefits. Our study focused on assessing the bioactive characteristics of EPS produced by Limosilactobacillus fermentum LAB1, lactic acid bacterium (LAB) isolated from the popular dairy beverage Borhani. Previous research had demonstrated its robust antimicrobial potential against various pathogens and provided genomic evidence of its EPS production. In this investigation, we verified and validated the EPS production ability of LAB1 through a battery of tests including the string test, Congo red agar test, and aniline blue agar plate method, all of which produced positive results. The EPS extracted from LAB1 displayed a high carbohydrate-to-protein ratio and exhibited a multifaceted repertoire of bioactive properties. It demonstrated antimicrobial activity against both Gram-positive and Gram-negative pathogens, and showed the ability to inhibit biofilm formation in Staphylococcus aureus (76.61%) and Escherichia coli (13.64%). Furthermore, the EPS exhibited DPPH free radical scavenging (92.25%), hydroxyl radical scavenging (87.82%), and reducing power capacity (3.1 mM/L), which indicate its substantial antioxidant potential. Additionally, the EPS sample demonstrated significant anti-inflammatory activity (75.79 %) and moderate oil emulsifying capacity with an emulsification index of 38.38%. These findings underscore the versatility of LAB1 EPS, positioning it for diverse applications and highlighting its multifunctional role across various industrial domains.

Determination of antibiotic resistance and biofilm formation in Klebsiella strains isolated from bovine mastitis cases

Mastitis is diseases of dairy cows with a high economic impact. Bovine mastitis is caused by a wide range of bacterial pathogens. As one of the major environmental pathogens Klebsiella ssp. was investigated in this study by some phenotypic characteristics like antibiotic resistance patterns and biofilm formation properties. A number of 483 cows by dairy farms around the Konya were examined by California Mastitis Test (CMT) producing 36 positive in terms of subclinical mastitis. A further 19 samples from clinical mastitic udders were also collected. Samples were inoculated onto Trypticase Soy Agar medium enriched with sheep blood and incubated aerobicaly for 24-48 hours at 37 °C. By morphological, biochemical and cultural charcateristics 14 isolates out of 37 coliform were identified as Klebsiella ssp. The double disc synergy method and Congo Red Agar test were used to perform antibiotic susceptibility and in vitro slime forming properties, respectively. Resistances to the antibiotics Ampicillin, Carbenicillin, Cephotaxime, Chloramphenicol, Erythromycin, Gentamicin, Neomycin, Oxytetracycline, Sulphamethoxazole/Trimpethoprim, Amoxicillin-Clavulanate and Imipenem were 78.5%, 78.5%, 35.7%, 42.8%, 100%, 7%, 7%, 50%, 14%, 21% and 7%, respectively. Three of the total isolets produced biofilm only. This appears to the first report on ESBL producing Klebsiella ssp from subclinical cases of bovine mastitis in Konya, Türkiye. Presently, two numbers of antimicrobial combinations to treat bovine cases are recommended by this work. In conclusion, because of costly challange nature of Klebsiella caused bovine mastitis implemantation of an effective mastitis control program should be used in local farms from Konya.

Resistance profile from staphylococcus aureus and pseudomonas aeruginosa obtained from tracheostomized children in the four seasons of the year

Objective: The objective of this study was to microbiologically characterize the tracheal secretion of tracheostomized children, evaluate biofilm formation and study the phenotypic and molecular profile of the antimicrobial resistance of Sthapylococcus aureus and Pseudomonas aeruginosa isolates. Methods: 88 samples of tracheal secretions were collected. The material was processed to perform phenotypic tests and bacterial identification. Tests were used to identify biofilms using Congo red agar test and microdilution in a 96-well plate, and the qPCR method was used to verify resistance. Results: Twelve Staphylococcus aureus samples and 30 Pseudomonas aeruginosa were isolated of pediactric tracheostomized patients. All the S. aureus samples were positive to biofilm formation in Congo red agar test. In the antibiogram test, S. aureus showed resistance to seven antimicrobials. Regarding the identification of resistance genes, blaZ was amplified in 57.1% and mecA in 28.6% of the isolated S. aureus. Pseudomonas aeruginosa showed blaOXA with 66,7% e blaKPC with 58,3%. In plasmid DNA, blaNDM stood out with 58,3% positive. Conclusions: The control of resistant bacteria involved in biofilms in the stoma of tracheostomized patients is a great challenge, since the simple cannula change does not always allow the control of the microbiota, which increases the vulnerability of patients to future respiratory complications.

Elimination of Biofilm Produced by Klebsiella Pneumonia Using Strontium Radioactive Sources (Sr90)

The aim of this study was conducted to elimination biofilm production from K. pneumonia by Sr90 radiosources inorder to removal biofilm that contained with K. pneumonia infection by beta ray. Study design and study populations of 100 isolates of K. pneumonia that identified by Vitek2GN, results of identification for all isolates approve are K. pneumonia. Study production of biofilm achieved by Congo red agar test, positive results by formation black colony on Congo red agar and negative results with red colony on Congo red agar. Influence Strontium Sr90 on K. pneumonia with dose D*(1hr.) 0.73251*10-2 msV; D*(2hr.) 1.46502*10-2 msV; D*(3hr.) 2.19753*10-2 msV; D*(4hr.) 2.93004*10-2 msV in different hours percentage of killing for this bacteria reach to 90% with control 300 colony, elimination of biofilm production from this bacteria by all doses in different time with formation pink color of colony compared with control formation black colony on Congo red agar, this results of affect by Strontium cause lost production biofilm by turn off into pink color when exposed to different doses of beta rays emitted from Strontium compared with control with black color.

Coagulase negative staphylococci from ovine bulk-tank milk: Effects of the exposure to sub-inhibitory concentrations of disinfectants for teat-dipping

Teat-dipping is one of the most effective methods to prevent mammary infections in ruminants, including sub-clinical mastitis caused by coagulase-negative staphylococci (CoNS). Improper disinfectant application could expose microorganisms to sub-inhibitory concentrations leading to phenotypic variations. In this study, 12 chlorhexidine-digluconate (CHDG)-tolerant (of which 4 qac positive) and 12 benzalkonium chloride (BC)-tolerant (of which 7 qac-positive) CoNS isolates from ovine milk were exposed to sub-inhibitory concentrations of CHDG and BC, respectively. Changes in disinfectant susceptibility against BC and CHDG, antibiotic resistance against 12 antibiotics and biofilm production were then assessed for both groups. After CHDG stress, 67 % and 83 % of the CHDG-stressed isolates doubled their MICs for BC and CHDG, respectively and 2 qac-negative isolates showed a four-fold increase of their MBCs for CHDG. After BC stress, MICs for BC and CHDG doubled in 58 % and 83 % of the BC-stressed isolates, respectively, while one qac-positive isolate increased four-fold the MIC for BC. Cross-resistance to antibiotics was assessed by disc diffusion method. Some qac-positive isolates varied their resistance profile, while a blaZ-positive isolate showed a resistant phenotype against ampicillin only after the exposure to the disinfectant. As for qac-positive isolates, one CHDG-stressed and 2 BC-stressed increased their resistance to kanamycin and cefoxitin, respectively. The Congo Red Agar test was carried out to assess the in vitro slime production: all isolates were negative after stress. In conclusion, sub-inhibitory exposure to disinfectants may affect disinfectant and antibiotic susceptibility, the latter in particular for qac-positive isolates and those hosting unexpressed antibiotic resistance genes.

The Ability of Staphylococcus spp. Isolated from Minced Meat to Adhere and form Biofilm on the Aluminum and Stainless-Steel Surfaces

The research included isolation and diagnosis of 19 bacterial isolate from 10 samples (minced meat and meat mincer), as 15 isolates belonging to the Micrococcaceae were diagnosed including 8 Staphylococcus spp. Isolates depending on the phenotypic properties and biochemical test, and in order to investigate the bacterial ability of the Micrococcaceae family to the formation of biofilms, two methods are used, the tube method and the Congo red agar method, as the results showed that all of the 15 isolates possess the ability to form biofilms as 100% depending on The tube method compared to the results of the Congo red agar test, which gave 13 positive result of 15 isolates in ratio 86.6% of the Micrococceae family. The highest rate of biofilm formation attributed to the Staphylococcus spp. which it gives 8 positive result for both tests as 100%. When comparing the adhesiveness of Staphylococcus spp. on the surface of the aluminum and stainless steel coupons as the materials used in the manufacture of meat mincers, our results showed that the adhesion and formation of biofilms were high on the surface of the aluminum coupons compared to the stainless steel coupons in the turbidity test using sonication and when investigating the total number of bacteria attached to the aluminum and steel coupons after exposing them to sonication, it was found that the number of units forming colonies CFU / cm2 for the aluminum coupons is 97 × 106, while it was found that CFU / cm2 of stainless steel coupons is 172 x 105, which enhances the turbidity comparison results.

Antimicrobial Resistance and Biofilm Formation by Staphylococcus aureus Isolated From Ocular Infections

Background: Untreated staphylococcal ocular infections may cause injuries in the ocular structure and lead to visual impairments, lesions in the anatomical ocular surface, and blindness. The aim of the study was to describe the characteristic of 90 Staphylococcus aureus (SA) strains from hospital and community treated ocular infections with a special emphasis on ability of biofilm formation and drug resistance. The biofilm formation was carried out using the Congo red agar (CRA) method applying Congo red dye. Studies have demonstrated that the CRA method is simple, fast, and repeatable and that modifications of some components can easily increase its accuracy. Methods: Biofilm formation was examined by the method with CRA test. On CRA, slime-producing strains formed black colonies, whereas nonproducing strains developed red colonies in 6 kinds of colors, from very red to very black: very red, red, burgundy, almost black, black, and very black. Antimicrobial susceptibility testing was performed by disc diffusion or the E-test method according to the current guidelines of the EUCAST. The MRSA, and MLSB phenotypes were detected. Polymerase chain reaction (PCR) was used to detect the mecA, and mupA genes. Erythromycin resistance genes (ermA, ermB, ermC, and msr) were detected by multiplex PCR. Results: A positive result of the CRA test was accomplished in 66.2% cases; significantly more often in hospital strains (73.4% vs 45.4%; OR, 3.3; 55% CI, 1.2–9.3). Moreover, 73.4% isolates were fully susceptible. In hospitalized patients, the level of resistance to at least 1 antimicrobial category has been identified as 40.9%, and this rate was 27.2% in outpatients. Among the tested strains, 5 (6.0%) had the resistance phenotype MRSA and 22 (26.5%) the resistance phenotype MLSB; 4 strains manifested both mechanisms; erythromycin resistance was 25.3% in those resistant to fluoroquinolones. Resistance to fluoroquinolones was 5 times more often found in ambulatory patients. All of the tested isolates were vancomycin sensitive. Conclusions: Biofilm formation is an important risk factor for developmental staphylococcal hospital-acquired ocular infections. Our results prove that hospital strains have demonstrated much greater biofilm-forming ability than nonhospital strains. Studies indicate the high efficacy of chloramphenicol and fluoroquinolones treatments, as well as the need to implement new solutions due to the aforementioned bacteria’s high resistance to neomycin and anatomic barriers difficulties.Disclosures: NoneFunding: None

Sheep mastitis Staphylococcus epidermidis biofilm effects on cell adhesion and inflammatory changes

Mastitis in sheep is an important disease as it causes a decrease in milk yield and quality. Staphylococcus epidermidis is recognized as the main cause of mastitis in sheep. Its ability to produce biofilm is believed to contribute to mammary gland pathology. The aim of this study was to assess the influence of S. epidermidis biofilm production on cell adhesion and on the inflammatory response of the mammary gland. A total of 109 S. epidermidis isolates from mastitic sheep milk samples were analyzed for in vitro slime production, assessed by Congo red agar test (CRA), and for biofilm formation, evaluated by tissue culture plate assay (TCP). The influence of biofilm production was estimated on the adherence of bacteria to mammary cells and on the mammary gland inflammatory reaction.Only 7.3% isolates produced slime on CRA and 8% produced biofilm according to TCP. The relation between slime production in CRA and biofilm production analyzed by TCP was highly significant (P < 0.001). The differences between biofilm production and different recorded inflammatory situations were non ­ significant (P ≥ 0.05). Adherence to mammary epithelium cells ranged from 0.05% to 1.23%. Biofilm production was not related to cell adhesion. Moreover, S. epidermidis isolates that induced different degrees of inflammation did not express differences in their ability to adhere to mammary epithelium. The present study suggests that biofilm production by sheep mastitis S. epidermidis is unlikely to affect either cell adhesion or mammary gland inflammatory response.

Biofilm formation and antibiotic resistance in Klebsiella pneumoniae urinary strains.

Multidrug-resistant Klebsiella pneumoniae has become a relevant healthcare-associated pathogen. Capsule, type 1 and 3 fimbriae (mrkA gene), type 2 quorum-sensing system (luxS), synthesis of D-galactan I (wbbM), LPS transport (wzm) and poly-beta-1,6-N-acetyl-D-glucosamine (pgaA) seem involved in K. pneumoniae biofilm. Nonenzymatic antibiotic resistance is related to nonexpression or mutation of porins (OmpK35 and OmpK36), and efflux pump (acrB) overexpression. The aim of this study was to analyse some virulence factors of K. pneumoniae isolates, and to evaluate possible correlations between their antibiotic resistance profile and ability to form biofilm. Quantitative biofilm production assay, congo red agar test and string test were performed on 120 isolates clustered in 56 extensively drug-resistant (XDR), 40 MDR and 24 susceptible (S) strains. Nine representative strains were analysed by real-time RT-PCR for the expression of antibiotic resistance (OmpK35, OmpK36, acrB) and biofilm production genes (mrkA, luxS, pga, wbbM, wzm) during planktonic and sessile growth. XDR isolates showed a higher ability to form biofilm (91·07%) and to produce polysaccharides (78·57%) when compared to MDR and S strains. In biofilm-growing XDR strains, seven of eight genes were upregulated, with the only exception of OmpK36. XDR strains exhibited phenotypic and genotypic features supporting a significant growth as biofilm. This study produces new findings that highlight a positive correlation between antibiotic resistance profile and biofilm-forming ability in XDR K. pneumoniae strains. These new evidences might contribute to the progress in selection of therapeutic treatments of infections caused by K. pneumoniae resistant also to the 'last line of defence' antibiotics, that is, carbapenems.

Sub-Inhibitory Concentrations of Rifampicin Strongly Stimulated Biofilm Production in S. aureus.

Background and Objectives: Staphylococcus aureus is an important pathogen and a frequent cause of infections associated with biofilm production in implantable medical devices. Biofilm production can be induced by sub-inhibitory concentrations (sub-MICs) of certain antibiotics, but few studies have researched this occurrence in S. aureus. In this study, we investigated the effect of sub-MICs of rifampicin and minocycline on biofilm production by five clinical and five non-clinical S. aureus isolates.Methods:Microtiter Plate assay and Congo Red Agar Test were used to analyze the biofilm production. The biofilm composition was evaluated by the detachment assay with sodium metaperiodate and proteinase K.Results:Rifampicin sub-MICs induced very high biofilm formation in seven isolates that were non-producers in Tryptic Soy Broth. In one producer isolate, the biofilm formation level was not affected by sub-MICs of this drug. Sub-MICs of minocycline did not induce biofilm production in all isolates tested and in two producer isolates, instead, MIC/2 and MIC/4 inhibited biofilm production. The results of the drugs in combination were similar to those with rifampicin alone. The biofilm matrix was identified as polysaccharide, except for one producer isolate, classified as proteinaceous. Polysaccharide biofilm producer isolates, when grown on Congo Red Agar without sucrose, but with sub-MICs of rifampicin, showed results in agreement with those obtained in Microtiter Plate Test.Conclusion:The high biofilm production induced by sub-MICs of rifampicin has potential clinical relevance, because this is one of the drugs commonly used in the impregnation of catheters. In addition, it is used adjunctively to treat certain S. aureus infections.

Clonal persistence of Salmonella enterica serovars Montevideo, Tennessee, and Infantis in feed factories.

Novel molecular techniques applied in biotechnology research have provided sound evidence on clonal persistence of distinct serovars of Salmonella in feed factory environments, over long periods of time (months, even years), which can be responsible for repeated in-house contamination of final products. In this study, we examined the possibility of clonal persistence of isolates of three Salmonella serovars that have been repeatedly identified in animal feed samples from three feed factories throughout a two-year period. The isolates Salmonella enterica serovars Tennessee (n = 7), Montevideo (n = 8), and Infantis (n = 4) were tested for genetic diversity using pulsed-field gel electrophoresis (PFGE) and multicellular behavior patterns by applying the Congo red agar test. SpeI and XbaI macro-restriction profiles indicated that isolates S. Montevideo and S. Infantis were identical, whereas isolates of S. Tennessee demonstrated greater genetic diversity, although the genetic differences did not exceed 10%. All Salmonella serovars demonstrated the ability to produce predominant matrix compounds essential for biofilm formation, curli fimbriae and cellulose. The identification of identical clones of S. Montevideo and S. Infantis, as well as the minor genetic diversity of S. Tennessee, which have been repeatedly isolated from animal feed in three production plants throughout a two-year period, indirectly suggests the possibility of their persistence in feed factory environments. Their ability to express the key biofilm matrix components further supports this hypothesis.

Analysis of S. Epidermidis icaA and icaD genes by polymerase chain reaction and slime production: a case control study

BackgroundStaphylococcus epidermidis is a common pathogen in medical device-associated infections and have an ability to form adherent slime. We aimed to study the effects of icaA and icaD genes on the slime formation of Staphylococcus epidermidis associated with catheter-associated infections.MethodsS. epidermidis isolates from the central venous catheter blood of patients with catheter-associated infections, and from the nasal vestibules of healthy volunteers, intensive care unit hospital staff, and patients, were collected. Slime phenotype was determined by Congo red agar test. The icaA/D was detected by polymerase chain reaction. Slime was examined using scanning electron microscopy.ResultsA total of 82 S. epidermidis isolates were collected. We found a statistically significant difference with regards to slime production between the clinical isolates from the catheter blood specimens and those from the nasal vestibules (p<0.05). All S. epidermidis slime positive strains isolated were icaA positive. There was a greater correlation between the presence of both icaA and icaD and the slime production than the single expression of icaA or icaD and the presence of slime in all groups. The co-expression of mecA and icaD was associated with enhanced resistance to antibiotics.ConclusionS. epidermidis bacteria are significant nosocomial pathogens, and icaA/D can clarify the adhesion mechanism in the pathogenesis of infections associated with medical devices. This study result could be useful for the development of rapid diagnosis for slime producing and methicillin resistant S. epidermidis strains.

Comparison of methods for the detection of biofilm formation by Staphylococcus aureus isolated from bovine subclinical mastitis

Biofilm formation is considered to be a selective advantage for Staphylococcus aureus mastitis isolates by facilitating bacterial persistence in the udder. It requires attachment to mammary epithelium, proliferation and accumulation of cells in multilayers. The objective of this study was to determine the sensitivity and specificity of three techniques for the detection of S. aureus biofilm-positive strains. Two phenotypic tests, including growth on microtitre plates and Congo red agar, were compared with a PCR technique using 94 S. aureus strains obtained from cows with subclinical mastitis from two farms in the state of São Paulo. These strains were characterised by in vitro slime production on Congo red agar, biofilm formation on microtitre plates and the presence of the icaA and icaD genes. The results revealed that 85% of the isolates tested produced slime on the Congo red agar, 98.9% of the isolates produced biofilms in vitro by adhering to sterile 96-well “U” bottom polystyrene tissue culture plates, and 95.7% of the isolates carried the icaA and icaD genes. The results of the phenotypic tests for biofilm formation were compared with those of the molecular analysis, and the sensitivity and specificity of the Congo red agar test were 88.9% and 100%, respectively, while those of the microtitre plate test were 100% and 25%, respectively. When the phenotypic methods for the detection of biofilm producers, namely growth on microtitre plates and Congo red agar, were compared, the sensitivity and specificity were 86% and 100%, respectively. Therefore, growth on Congo red agar and the microtitre plate test are methods that could be used to determine whether an isolate has the potential for biofilm production.

Antimicrobial resistance of Staphylococcus spp. from small ruminant mastitis in Brazil

The study aimed to determine the antimicrobial resistance patterns and to identify molecular resistance markers in Staphylococcus spp. (n=210) isolated from small ruminant mastitis in Brazil. The antimicrobial resistance patterns were evaluated by the disk diffusion test and by detection of the presence of mecA, blaZ, ermA, ermB, ermC and msrA genes by PCR. The efflux pump test was performed using ethidium bromide and biofilm production was determined by Congo red agar test along with PCR for detection of the icaD gene. The isolates were most resistant to amoxicillin (50.0%), streptomycin (42.8%), tetracycline (40.4%), lincomycin (39.0%) and erythromycin (33.8%). Pan-susceptibility to all tested drugs was observed in 71 (33.8%) isolates and 41 Staphylococcus isolates were positive for the efflux pump. Although phenotypic resistance to oxacillin was observed in 12.8% of the isolates, none harbored the mecA gene. However, 45.7% of the isolates harbored blaZ indicating that beta-lactamase production was the main mechanism associated with staphylococci resistance to beta-lactams in the present study. The other determinants of resistance to antimicrobial agents ermA, ermB, ermC, and msrA were observed in 1.4%, 10.4%, 16.2%, and 0.9% of the isolates, respectively. In addition, the icaD gen was detected in 32.9% of the isolates. Seventy three isolates (54 from goats and 19 from sheep) were negative for all resistance genes tested and 69 isolates presented two or more resistance genes. Association among blaZ, ermA, ermB, ermC and efflux pump were observed in 17 isolates, 14 of which originated from goats and three from sheep. The data obtained in this study show the resistance of the isolates to beta-lactamics, which may be associated with the use of antimicrobial drugs without veterinary control.

Evaluation of different detection methods of biofilm formation in clinical Candida isolates.

Biofilm is one of the known virulence factors of Candida, an important pathogen and commensal. Early detection of biofilm production may be useful for clinical decision because of its suggestive property for potential pathogenic capacity of Candida isolates. In this study, we simultaneously screened 411 clinical isolates of Candida spp. by microtiter plate (MTP), visual tube (TM) and congo red agar (CRA) methods for determining their ability to form biofilm and also evaluated the reliability of these methods in order to determine most suitable screening method. The accuracy of TM and CRA methods were also evaluated by using MTP as reference method. Of the 411 Candida spp., 159 (38.7%) displayed a biofilm-positive phenotype by MTP method. Sensitivity and specificity of the tube method were 68 and 98%, respectively and the positive predictive value (PPV) was 97% and the negative predictive value (NPV) was 83%. The sensitivity for congo red agar test was 79% and the specificity was 99%, and the PPV was 99% and the NPV was 88%. Tube method showed very good agreement for the isolates producing strong biofilm, whereas differentation of isolates producing weak biofilm was difficult. By the congo red method, classification of existing biofilm was problematic. Among the three methods studied, microtiter plate method may be suggested as the most sensitive method, which is easy to conduct and applicable as a routine process. Key words: Candida, biofilm, microtiter plate, tube method, congo red agar.

A comparative analysis of phenotypic and genotypic methods for the determination of the biofilm-forming abilities of Staphylococcus epidermidis

The collection of 146 Staphylococcus epidermidis strains isolated from the nasopharynx of lung cancer patients has been studied for the ability of slime secretion and biofilm formation using the Congo red agar (CRA) test and the microtiter plate (MtP) method, respectively. The prevalence of the icaAD and the aap genes was also analyzed. Some isolates (35.6%) were biofilm positive by the MtP method, while 58.9% of isolates exhibited a slime-positive phenotype by the CRA test. The sensitivities of the CRA test evaluated using the MtP method as a gold standard of biofilm production were 73.1%, 97.3% and 13.3% for all the strains screened, ica-positive and ica-negative strains, respectively. The genotype ica(+)aap(+) was correlated with a strong biofilm-producer phenotype. Interestingly, some of the ica(-)aap(-) isolates could also form a biofilm. The correlation between the presence of icaAD genes and the biofilm-positive phenotype by the MtP method as well as slime production by the CRA test was statistically significant (P<0.0001). However, some S. epidermidis strains possess the potential ability of ica-independent biofilm formation; thus, further studies are needed to determine reliable, short-time criteria for an in vitro assessment of biofilm production by staphylococci.

Correlation of Slime Production Investigated via Three Different Methods in Coagulase-Negative Staphylococci with Crystal Violet Reaction and Antimicrobial Resistance

This study investigated slime production by coagulase-negative staphylococci (CNS) using the standard tube (ST), Congo red agar (CRA) plate and Christensen's tube (CT) methods, and compared the results with those of the crystal violet reaction (CVR) test. The potential correlation between slime production and antimicrobial resistance was also evaluated. In total, 205 CNS strains were isolated from biological samples: 92 (44.9%) were shown to produce slime by the ST method; 96 (46.8%) by the CRA plate method; 90 (43.9%) by the CT method; and 89 (43.4%) strains were CVR positive. Eighty-three (40.5%) CNS strains were positive for slime production by the ST, CRA and CT methods. The findings of the ST, CRA and CT test methods were consistent with each other but were not related to CVR positivity. Based on the ST method, rates of antibiotic resistance to several antimicrobial agents were higher in slime-positive strains than in slime-negative strains and, in some cases, this was statistically significant.

Biofilm production, a marker of pathogenic potential of colonizing and commensal staphylococci

Biofilm is one of the known virulence factors of staphylococci, a human and animal pathogen and commensal. Some of the strains become invasive under favorable conditions while others do not cause disease. Early detection and management of potentially pathogenic staphylococci is the essential step to prevent device-associated infections. There is also a need to evaluate one simple method for the detection of potential pathogens. Hence this study was planned to study the difference in potential of commensal, colonizing and invasive strains of staphylococci to produce biofilm. We used one qualitative (Congo red agar) and one quantitative (microtiter plate) method for detection of biofilm production and evaluated the sensitivity and specificity of Congo red agar method by using microtiter plate method as a gold standard. We consecutively enrolled staphylococcal strains isolated from peripheral intravenous device (IVD), venous blood, site of IVD insertion and nasal mucosa of patients admitted to pediatric ward with peripheral intravenous devices in place for more than 48 h. Total 100 invasive, 50 colonizing and 50 commensal isolates were studied. Of 100 invasive isolates 74% (74/100) were biofilm positive while only 68% (34/50) colonizing and 32% (16/50) commensal isolates were biofilm positive. The difference in biofilm production by commensal, colonizing and invasive strains was statistically significant ( p < 0.0001). Sensitivity and specificity of Congo red agar test for detection of biofilm producers were 90.63% and 90.79% for Staphylococcus aureus and 75.86% and 96.88% respectively for coagulase negative staphylococci. CRA is a method that could be used to determine whether an isolate has the potential for biofilm production or not.

Strong slime production is a marker of clinical significance in Staphylococcus epidermidis isolated from intravascular catheters

Biofilm production was assessed in 52 Staphylococcus epidermidis isolates from the catheters of 52 patients with catheter-related bloodstream infections (CR-BSI) and compared with 14 isolates from the skin of healthy volunteers by spectrophotometry. The isolates were classified as non- (G1), weak- (G2) or strong- (G3) slime producers based on optical density, and as producers and non-producers based on the results of the Congo red agar test. Differences (p = 0.012) in the proportion of G1, G2 and G3 among the isolates were found between catheter and healthy skin strains: there was a higher percentage of G1 types among the healthy skin strains (35.7 vs. 11.5%; p = 0.046) and a higher percentage of G3 types among the catheter isolates (44.2 vs. 0%; p = 0.001). No significant differences were found with the Congo red agar test. G3 is a phenotypic marker for CR-BSI.