Prevalence of icaA and icaD Genes of Staphylococcus aureus and Staphylococcus epidermidis Strains Isolated from Patients and Hospital Staff

Prevalence, antimicrobial resistance, and genetic lineages of nasal Staphylococcus aureus among medical students at a Spanish University: detection of the MSSA-CC398-IEC-type-C subclade

Medical students could be a potential source of Staphylococcus aureus transmission to patients. This cross-sectional study involved samples collected from both nasal nostrils. Samples were processed for S. aureus recovery; the antimicrobial resistance (AMR) phenotype was determined by disc diffusion assays and the spa types and AMR genotypes by PCR/sequencing. A structured questionnaire was administered to students to collate data related to potential risk factors of nasal colonization. Ninety-eight students were included, 50 % were colonized by S. aureus and 12.2 % by MRSA. The mecA gene was detected in all MRSA isolates. The MSSA-CC398-IEC-type C lineage was found among 16.3 % of nasal carriers, of which t571 was the predominant spa-type. MRSA isolates were ascribed to spa types t2226 (CC5, 12 isolates) and t3444 (new spa type, 1 isolate). All MRSA were multi-drug resistant and MSSA were predominantly resistant to erythromycin-clindamycin (inducible-type, mediated by ermT gene). High rates of S. aureus and MRSA nasal carriages were observed in this study. The predominance of the CC398 lineage among MSSA (emergent invasive lineage) represent a relevant finding of public health concern. The role of medical students as potential source of MRSA and MSSA-CC398 transmissions in hospital and community needs to be elucidated in detail.

The Determination, Monitoring, Molecular Mechanisms and Formation of Biofilm in E. coli

Biofilms are cell assemblies embedded in an exopolysaccharide matrix formed by microorganisms of a single or many different species. This matrix in which they are embedded protects the bacteria from external influences and antimicrobial effects. The biofilm structure that microorganisms form to protect themselves from harsh environmental conditions and survive is found in nature in many different environments. These environments where biofilm formation occurs have in common that they are in contact with fluids. The gene expression of bacteria in complex biofilm differs from that of bacteria in the planktonic state. The differences in biofilm cell expression are one of the effects of community life. Means of quorum sensing, bacteria can act in coordination with each other. At the same time, while biofilm formation provides many benefits to bacteria, it has positive and negative effects in many different areas. Depending on where they occur, biofilms can cause serious health problems, contamination risks, corrosion, and heat and efficiency losses. However, they can also be used in water treatment plants, bioremediation, and energy production with microbial fuel cells. In this review, the basic steps of biofilm formation and biofilm regulation in the model organism Escherichia coli were discussed. Finally, the methods by which biofilm formation can be detected and monitored were briefly discussed.

Phenotypic and Genotypic Characterization of Antibiotic Resistance in Staphylococcus aureus Isolated from Different Sources

Background: Staphylococcus aureus is a bacterial pathogen that can cause a wide range of nosocomial infections. Nasal colonization by S. aureus plays an important role both in the epidemiology and pathogenesis of infection. Objectives: This study aimed at detecting the biofilm-forming capacity of clinical isolates and detection of icaA and agr genes. Methods: A total of 150 clinical specimens was collected from patients in different hospitals in Baghdad. The clinical samples included wounds, abscess, sputum, and ear infections. The suspected isolates were cultured for one day at 37 °C on mannitol salt agar in an aerobic environment. Results: The results showed that of 150 samples, 44 isolates were S. aureus (29.3%), of wounds samples, 22 isolates (45.83%) were S. aureus, 13 (37.14%) were from abscess, 7 (17.95%) from sputum, and 2 isolates (7.14%) from ear samples. This study found that most isolates formed biofilm, but the levels of biofilm were distributed across three ranges. The results also indicated that 47.7% of the isolates produced a strong biofilm, as well as 38.6 and 13.6% produced moderate and weak biofilms, respectively. The present molecular results showed that S. aureus from different samples were 13 (59.1%), 4 (30.77%), 3 (42.85%), 0 (0%) from wounds, abscess, sputum, ear, respectively, were positive for agr gene. While the results showed 18 (81.8%), 10 (76.9%), 5 (71.4%), 1 (50%), respectively, were positive for icaA gene. Conclusions: Most S. aureus isolates isolated from wound were biofilm positive. These isolates bore icaA and agr genes in a high quantity.

Multidrug resistant staphylococci isolated from pigs with exudative epidermitis in North eastern Region of India

Exudative epidermatitis or greasy pig disease (GPD) is a contagious disease of pig and endemic worldwide caused by toxigenic strains under genus Staphylococcus. The present study reported an outbreak of GPD in Champhai district of Mizoram adjoining to the southern border of Myanmar. A total of 60 samples were collected from 22 clinically affected animals and processed for isolation and identification of Staphylococcus spp. All the isolates were subjected to antimicrobial sensitivity assay, biofilm production assay and detection of virulence genes, biofilm genes and mec genes followed by cloning and sequencing for phylogenetic analysis. A total of 44 staphylococci belonged to four species (S. sciuri, S. aureus,S. lentus, and S. hyicus) were isolated. Majority of the isolates were multidrug resistant with maximum resistance against ampicillin, penicillin including vancomycin. None of the S. hyicus isolates was methicillin resistant (MRSH) but 66·67% isolates were MRSA. By PCR, mecA gene was detected in S. aureus (n = 2), S. sciuri (n = 4) and S. lentus (n = 3). Biofilm associated gene icaD was detected in S. aureus (n = 3), S. sciuri (n = 5), S. hyicus (n = 4) and S. lentus (n = 6). The exfoliative toxin genes (ehxB, shetA and tsst1) were detected in S. hyicus (n = 3) and S. aureus (n = 1) isolates. All the isolates were closely related with the isolates from pigs of China, Germany, Japan and USA. The pathogens might be transmitted through illegal migration of pigs from Myanmar to India.

The Correlation between icaA and icaD Genes with Biofilm Formation Staphylococcus epidermidis In Vitro

This study was conducted to identify the presence of icaA and icaD genes in S. epidermidis and to analyze the relationship between the presence of icaA and icaD genes with the ability of in vitro biofilm formation in S. epidermidis. S. epidermidis isolates from patients and healthy people were collected and PCR was examined to detect icaA and icaD genes. which then continued to examine the ability of biofilm formation by the method of Congo Red Agar. The results of this genotypic and phenotypic examination were then tested for correlation with statistical tests using SPSS 23.0. A total of 40 S. epidermidis isolates were collected, consisting of 20 clinical isolates and 20 isolates of normal flora. The icaA gene was positive in 5 isolates (12.5%), and 8 isolates (20%) were positive for the icaD gene, 3 isolates with icaA and icaD were both positive. One hundred percent of isolates with icaA or icaD positively formed biofilms, but there were 15 isolates (42.9%) who did not have the icaA gene but showed the ability to form biofilms, while 12 isolates (37.5%) who did not have the icaD gene also formed biofilms. Fifty percent of S. epidermidis isolates showed the ability to form biofilms at CRA. The Fisher Exact test showed a significant relationship between the icaA gene and the ability of biofilm formation (p=0.047 (p<0.05)) as well as the icaD gene (p=0.03 (p<0.05)). The icaA and icaD genes have a significant relationship to biofilm formation in S. epidermidis. There was another mechanism in the formation of biofilms that are not dependent on the ica gene.

A synergistic association between adhesion-related genes and multidrug resistance patterns of Staphylococcus aureus isolates from different patients and healthy individuals

OBJECTIVES

Biofilm -forming capacity of Staphylococcus aureus (S. aureus) as a commensal opportunistic bacterial species induce a growth in antibiotic resistance in chronic diseases. Since expression of biofilm- related genes and antibiotic resistance function are interdependent, the present study was an attempt to inquire biofilm formation and its relationship with antibiotic resistance in clinical isolates.

METHODS

208 S. aureus clinical isolates from four major provinces of Iran were investigated in terms of presence of adhesion genes (icaA, icaD, icaB, icaC, fnbpA, fnbpB, clfA, clfB, cna, sasC, sasG and bap) using PCR. In addition, microtiter plate (Mtp) assay was performed to examine quantitative biofilm formation of the isolates and their antibiotic resistance patterns against 16 antibiotics determined upon CLSI criteria.

RESULTS

The results revealed high prevalence rate (almost 100%) of icaADBC and MSCRAMMs genes in the isolates. Moreover, bap gene was not detected in any of the tested clinical isolates. Based on phenotypic method 169 isolates (81.25%) were also found to have biofilm formation ability. Among 208 isolates, 98 (47.12%) isolates were multidrug resistant (MDR). Vancomycin, linezolid, nitrofurantoin and quinupristin/dalfopristin were the most effective drugs against MDR strains. Furthermore, the findings demonstrated a significant relationship between MDR and biofilm forming capacity.

CONCLUSION

Prevalence rate of adhesion- related genes was high in S. aureus from isolates in Iran ;so these genes might be expressed under certain conditions and cause emergence of MDR strains. Therefore, further investigations are necessary to prevent initial attachment based on new candidate adhesion genes for vaccine design.

Association of intercellular adhesion gene A with biofilm formation in staphylococci isolates from patients with conjunctivitis

BACKGROUND

There is a great negative impact of biofilm-mediated infection on patient health which necessitates the use of reliable methods for detecting biofilm producers.

AIMS

This study was done to determine biofilm-producing ability and the presence of intercellular adhesion gene A in clinical staphylococcal isolates and to assess the reliability of two phenotypic methods used for biofilm detection.

MATERIALS AND METHODS

Fifty staphylococcal strains were isolated from 100 conjunctival swabs from patients attended the Ophthalmology Outpatient Department of the Research Institute of Ophthalmology. Two phenotypic methods were used for detection of biofilm production; qualitative congo red agar (CRA); and quantitative microtiter plate. Polymerase chain reaction was used to determine the presence of icaA gene.

RESULTS

In Staph aureus, 60% were positive biofilm forming and 40% were negative biofilm forming by both phenotypic methods. All positive biofilm-forming isolates were positive for icaA gene production. In coagulase negative staph, 50% were positive biofilm forming and 50% were negative biofilm forming by both phenotypic methods. All positive biofilm-forming strains were positive for icaA gene. All negative cases by CRA and microtiter plate methods were negative for icaA gene except two isolates. All staphylococcal isolates were subjected to antibiotic susceptibility test to correlate biofilm formation with multidrug resistance in staph.

CONCLUSION

There is high significant correlation between icaA gene presence and biofilm forming ability; however, the biofilm-forming ability of some isolates in the absence of icaA gene highlights the importance of further genetic investigations of ica-independent biofilm formation mechanisms.

Inflammatory cytokines and biofilm production sustain Staphylococcus aureus outgrowth and persistence: a pivotal interplay in the pathogenesis of Atopic Dermatitis

Individuals with Atopic dermatitis (AD) are highly susceptible to Staphylococcus aureus colonization. However, the mechanisms driving this process as well as the impact of S. aureus in AD pathogenesis are still incompletely understood. In this study, we analysed the role of biofilm in sustaining S. aureus chronic persistence and its impact on AD severity. Further we explored whether key inflammatory cytokines overexpressed in AD might provide a selective advantage to S. aureus. Results show that the strength of biofilm production by S. aureus correlated with the severity of the skin lesion, being significantly higher (P < 0.01) in patients with a more severe form of the disease as compared to those individuals with mild AD. Additionally, interleukin (IL)-β and interferon γ (IFN-γ), but not interleukin (IL)-6, induced a concentration-dependent increase of S. aureus growth. This effect was not observed with coagulase-negative staphylococci isolated from the skin of AD patients. These findings indicate that inflammatory cytokines such as IL1-β and IFN-γ, can selectively promote S. aureus outgrowth, thus subverting the composition of the healthy skin microbiome. Moreover, biofilm production by S. aureus plays a relevant role in further supporting chronic colonization and disease severity, while providing an increased tolerance to antimicrobials.

Role of Intracellular Adhesion icaAD and agr genes in Biofilm Formation in Clinical S. aureus Isolates and Assessment of Two Phenotypic Methods

Objective:

To determine the role of icaAD and agr genes in biofilm formation and evaluate the consistency of two phenotypic methods for biofilm measurement.

Methods:

A total of 81 clinical S. aureus strains were included and analyzed for biofilm formation by two methods. The microtitration plate method was optimized using computational fluid dynamics and compared with the Congo red assay. The genes for icaAD and agr were detected using PCR.

Results:

Of 81 isolates, biofilm production was detected in 43% isolates using Congo red method while microtiter plate assay showed biofilm production in 92% isolates. Both methods showed correlation in 30% isolates. PCR detection showed icaAD gene in 42 (52%) isolates. Out of 81 S. aureus isolates 65 strains (80%) contained agr while 16 (20%) strains were non-typeable.

Conclusions:

In conclusion, biofilm production was observed for both agr positive and agr negative isolates. Furthermore, the presence of icaAD genes was not associated with all biofilm producing strains as some strains negative for icaAD genes displayed biofilm production.

The antifungal caspofungin increases fluoroquinolone activity against Staphylococcus aureus biofilms by inhibiting N-acetylglucosamine transferase

Biofilms play a major role in Staphylococcus aureus pathogenicity but respond poorly to antibiotics. Here, we show that the antifungal caspofungin improves the activity of fluoroquinolones (moxifloxacin, delafloxacin) against S. aureus biofilms grown in vitro (96-well plates or catheters) and in vivo (murine model of implanted catheters). The degree of synergy among different clinical isolates is inversely proportional to the expression level of ica operon, the products of which synthesize poly-N-acetyl-glucosamine polymers, a major constituent of biofilm matrix. In vitro, caspofungin inhibits the activity of IcaA, which shares homology with β-1-3-glucan synthase (caspofungin's pharmacological target in fungi). This inhibition destructures the matrix, reduces the concentration and polymerization of exopolysaccharides in biofilms, and increases fluoroquinolone penetration inside biofilms. Our study identifies a bacterial target for caspofungin and indicates that IcaA inhibitors could potentially be useful in the treatment of biofilm-related infections.

Biofilms formed by Staphylococcus aureus are poorly responsive to antibiotics. Here, Siala et al. show that an antifungal drug (caspofungin) enhances the activity of fluoroquinolone antibiotics against S. aureus biofilms by inhibiting an enzyme involved in synthesis of the biofilm matrix.

Comparison of Biofilm Formation between Methicillin-Resistant and Methicillin-Susceptible Isolates of Staphylococcus aureus

Background:

The aim of this study was to compare the biofilm formation and the prevalence of biofilm-associated genes between the isolates of methicillin-resistant (MRSA) and methicillin-susceptible (MSSA) Staphylococcus aureus.

Methods:

In total, 209 S. aureus isolates were collected. The antibiotic susceptibility test was conducted using nine antibiotics according to the guidelines of Clinical and Laboratory Standards Institute. Phenotypic biofilm formation was performed with microtiter plate assay. The polymerase chain reaction was employed to detect icaA, icaD, icaB, icaC, clfA, clfB, fnbA, fnbB, fib, cna,eno, ebps, bbp,mecA, and SCCmec types as well as agr group genes with specific primers.

Results:

Sixty-four (30.62%) isolates were resistant to methicillin, and 54 (83%) MRSA harbored SCCmec III. Furthermore, 122 (58.3%) isolates belonged to agr group I. Twenty-six (36.1%) MRSA and 42 (28.9%) MSSA isolates were strong biofilm producers (no significant difference). The prevalence of icaA, icaD, icaB, and icaC genes in MSSA isolates was 71, 41, 76, and 72%, respectively. The frequency of clfA, clfB, fnbA, fnbB, fib, cna, eno, ebps, and bbp in MSSA was 100, 100, 56, 46, 74, 54, 78, 11, and 1%, respectively. However, in MRSA isolates, the frequency was 97, 97, 64, 51, 76, 56, 79, and 12% with no track of bbp, respectively.

Conclusion:

Statistical difference between MSSA and MRSA regarding biofilm formation and the frequency of all biofilm-encoding genes was not significant. The majority of the S. aureus isolates harbored clfA, clfB, eno, fib, icaA, and icaD genes.

Molecular Characterization, Antibiotic Resistance, and Virulence Factors of Methicillin-Resistant Staphylococcus aureus Strains Isolated from Imported and Domestic Meat in Korea

During a nationwide surveillance in Korea, 13 methicillin-resistant Staphylococcus aureus (MRSA) strains were isolated from imported and domestic meat between 2009 and 2011. The predominant MRSA genotype was SCCmec type V, and only two agr types (I and II) were found. Unexpectedly, sequence type ST72 comprised more than 50% of the isolates; this is the first instance of type ST72 in food from Canada. Two Spanish pork isolates were ST398, which caused human disease in Europe, and they carried leukotoxin genes, lukS, lukF, and lukE-lukD. Furthermore, P71 and P6 harbored all of the known leukocidin genes, lukS-lukF-lukE-lukD-lukM. Our collected MRSA strains were multidrug resistant with various antimicrobial and heavy-metal resistance genes. Toxin genes that are commonly found in clinical MRSA also were detected in our meat strains. One MRSA strain exhibited an uncommon type of enterotoxin, sec-see-seg-sei-sel-sem-sen-seo-sep. Plasmids (1.5-15.0 kb) were found in 12 of the 13 MRSA isolates. Repetitive sequence-based polymerase chain reaction of the genomic DNA showed 3 clusters with 95% similarity. The presence of multidrug-resistant and toxigenic MRSA in meat products suggests that comprehensive surveillance should be continued for imported meats in Korea.

Presence of enterotoxigenic Staphylococcus aureus in artisan fruit salads in the city of San Luis, Argentina

An increase in the consumption of fruit juices and minimally processed fruits salads has been observed in recent years all over the world. In this work, the microbiological quality of artisan fruit salads was analysed. Faecal coliforms, Salmonella spp, Shigella spp, Yersinia enterocolitica and Escherichia coli O157:H7 were not detected; nevertheless, eleven strains of Staphylococcus aureus were isolated. By multiplex PCR, all isolates showed positive results for S. aureus 16S rRNA gene and 63.6% of them were positive for sea gene. Furthermore, PCR sea positive strains were able to produce the corresponding enterotoxin. Finally, the inactivation of these strains in fruit salads by nisin, lysozyme and EDTA, was studied. EDTA produced a total S. aureus growth inhibition after 60 h of incubation at a concentration of 250 mg/L. The presence of S. aureus might indicate inadequate hygiene conditions during salad elaboration; however, the enterotoxigenicity of the strains isolated in this study, highlights the risk of consumers' intoxication. EDTA could be used to inhibit the growth of S. aureus in artisan fruit salads and extend the shelf life of these products.

Detection of the intercellular adhesion gene cluster (ica) in clinical Staphylococcus aureus isolates

Staphylococcus aureus is a major hospital and community pathogen having the aptitude to cause a wide variety of infections in men. The ability of microorganisms to produce biofilm facilitates them to withstand the host immune response and is recognized as one factor contributing to chronic or persistent infections. It was demonstrated that the ica-encoded genes lead to the biosynthesis of polysaccharide intercellular adhesion (PIA) molecules, and may be involved in the accumulation phase of biofilm formation. Different studies have shown the decisive role of the ica gene as virulence factors in staphylococcal infections.

This study was carried out to demonstrate the relationship between ica gene and production of slime layer in S. aureus strains. Sixty S. aureus strains were isolated from patients. The isolates were identified morphologically and biochemically following standard laboratory methods. After identification, the staphylococcal isolates were maintained in trypticase soy broth (TSB), to which 15% glycerol was added, and stored at –20°C. Slime formation and biofilm assay was monitored. A PCR assay was developed to identify the presence of icaD (intercellular adhesion gene) gene in all isolates. Thirty-nine slime producing colonies with CRA plates (65%) formed black colors, the remaining 21 isolates were pink (35%). In the quantitative biofilm assay 35 (58%) produced biofilm while 25 (42%) isolates did not exhibit this property. All isolates were positive for detection of icaD gene by PCR method. The interaction of icaA and icaD in the investigated isolates may be important in slime layer formation and biofilm phenomena.

We propose PCR detection of the ica gene locus as a rapid and effective method to be used for discrimination between potentially virulent and nonvirulent isolates, with implications for therapeutic and preventive measures pertainin to the management of colonized indwelling catheters.

A combination of methods to evaluate biofilm production may help to determine the clinical relevance of Staphylococcus in blood cultures

Staphylococcus is the most prevalent pathogen causing bacteremia and many of its isolates possess the ability to form biofilm. In this study Staphylococcus isolates from the blood of patients with bacteremia were analyzed by two biofilm detection phenotypic methods: Congo red agar (CRA) and microtiter-plate adherence (MPA) in relation to the presence of ica genes, detected by PCR. Their oxacillin susceptibility was also evaluated. Among 127 isolates evaluated, 47 were S. aureus and 80 were coagulase negative staphylococci (CNS). Seventy-four (58.3%) isolates were mecA gene positive (27.7%S. aureus and 76.3% CNS isolates). Among the 40 S. aureus isolates which were positive for the ica genes, 25 (62.5%) were positive in MPA and 27 (67.5%) in CRA, whereas both methods combined detected 34 (85%) isolates as biofilm producers. Among 12 S. epidermidis isolates carrying ica genes, 8 were positive in MPA and 5 in CRA. The combination of CRA and MPA methods provided a better prediction of the presence of ica genes in S. aureus isolates than did either method alone.

Healthcare-associated infections at intensive care unit of department of anesthesiology and intensive medicine at Martin Faculty Hospital

We analyzed the occurrence of healthcare-associated infections (HAl) at intensive care unit of the Department of Anesthesiology and Intensive Medicine of Martin Faculty Hospital in 2008. We performed a retrospective-prospective observation according the protocol of European HELICS (Hospital in Europe Link for Infection Control and Surveillance) system. We found 11 HAl (4.45%) which on average prolonged the length of hospitalization by 6 days. The most frequent localisation of HAl was the respiratory tract. By our own observation we found the same number of HAl cases as it had been reported officially but the observed and reported cases do not match. The surveillance system HELICS uses definitions slightly different from those used in Slovakia. The severity of health status of a patient at admission influences the risk of HAl. We suggest a continuing collaboration on HELICS system with further involvement of all departments of Martin Faculty Hospital and creation of a hospital infection control team. We also suggest an improvement in testing for etiologic agents of HAl and an introduction of methods of molecular epidemiology in diagnostics, as well as quantification of costs related to occurrence of HAl and to assess an implication of automated monitoring system in HAl surveillance.

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.

Clinical implications of icaA and icaD genes in coagulase negative staphylococci and Staphylococcus aureus bacteremia in febrile neutropenic pediatric cancer patients

BACKGROUND

Staphylococci are the most frequently isolated organisms from blood cultures of febrile neutropenic (FN) cancer patients. We aimed to define the nature of these isolates by studying the prevalence of icaA and icaD genes in coagulase-negative staphylococci (CoNS) and Staphylococcus aureus isolates in relation to clinical and microbiological features.

PROCEDURE

Fifty-five CoNS and S. aureus isolates from blood cultures of FN pediatric patients receiving chemotherapy were tested for slime production using Congo red agar plate test (CRA test), and for the presence of icaA and icaD genes by PCR.

RESULTS

Of the CoNS isolates, eight were positive for ica genes, and three were slime positive/ica negative. A total of 11 (24.4%) cases of CoNS bacteremia were either ica genes or CRA test positive. There was a concordance between ica genes and CRA test positivity (P < 0.001). S. aureus isolates exhibited icaA and icaD genes more than CoNS isolates (P = 0.03). Vancomycin was significantly more prescribed in episodes of ica-positive cases (P = 0.029).

CONCLUSIONS

The results of the present study support the hypothesis that the ica genes are important virulence markers for clinically significant CoNS isolates, indicating their ability to produce slime. This could be used to assign a group with higher risk FN. On the other hand, absence of these genes may permit, along with other clinical criteria, the consideration of a low-risk FN episode and allow for safe early discharge.

Genetic evidence for an alternative citrate-dependent biofilm formation pathway in Staphylococcus aureus that is dependent on fibronectin binding proteins and the GraRS two-component regulatory system

We reported previously that low concentrations of sodium citrate strongly promote biofilm formation by Staphylococcus aureus laboratory strains and clinical isolates. Here, we show that citrate promotes biofilm formation via stimulating both cell-to-surface and cell-to-cell interactions. Citrate-stimulated biofilm formation is independent of the ica locus, and in fact, citrate represses polysaccharide adhesin production. We show that fibronectin binding proteins FnbA and FnbB and the global regulator SarA, which positively regulates fnbA and fnbB gene expression, are required for citrate's positive effects on biofilm formation, and citrate also stimulates fnbA and fnbB gene expression. Biofilm formation is also stimulated by several other tricarboxylic acid (TCA) cycle intermediates in an FnbA-dependent fashion. While aconitase contributes to biofilm formation in the absence of TCA cycle intermediates, it is not required for biofilm stimulation by these compounds. Furthermore, the GraRS two-component regulator and the GraRS-regulated efflux pump VraFG, identified for their roles in intermediate vancomycin resistance, are required for citrate-stimulated cell-to-cell interactions, but the GraRS regulatory system does not impact the expression of the fnbA and fnbB genes. Our data suggest that distinct genetic factors are required for the early steps in citrate-stimulated biofilm formation. Given the role of FnbA/FnbB and SarA in virulence in vivo and the lack of a role for ica-mediated biofilm formation in S. aureus catheter models of infection, we propose that the citrate-stimulated biofilm formation pathway may represent a clinically relevant pathway for the formation of these bacterial communities on medical implants.