Genetic polymorphism of the accessory gene regulator (agr) locus in Staphylococcus epidermidis and its association with pathogenicity

Analysis of the Presence of the Virulence and Regulation Genes from Staphylococcus aureus (S. aureus) in Coagulase Negative Staphylococci and the Influence of the Staphylococcal Cross-Talk on Their Functions

Coagulase-negative staphylococci (CoNS) are increasingly becoming a public health issue worldwide due to their growing resistance to antibiotics and common involvement in complications related to invasive surgical procedures, and nosocomial and urinary tract infections. Their behavior either as a commensal or a pathogen is a result of strict regulation of colonization and virulence factors. Although functionality of virulence factors and processes involved in their regulation are quite well understood in S. aureus, little is known about them in CoNS species. Therefore, the aim of our studies was to check if clinical CoNS strains may contain virulence factors and genes involved in resistance to methicillin, that are homologous to S. aureus. Moreover, we checked the presence of elements responsible for regulation of genes that encode virulence factors typical for S. aureus in tested isolates. We also investigated whether the regulation factors produced by one CoNS isolate can affect virulence activity of other strains by co-incubation of tested isolates with supernatant from other isolates. Our studies confirmed the presence of virulence factor and regulatory genes attributed to S. aureus in CoNS isolates and indicated that one strain with an active agr gene is able to affect biofilm formation and δ-toxin activity of strains with inactive agr genes. The cognition of prevalence and regulation of virulence factors as well as antibiotic resistance of CoNS isolates is important for better control and treatment of CoNS infections.

Dissemination of epidemic ST239/ST241-t037-agrI-SCCmecIII methicillin-resistant Staphylococcus aureus in a Tunisian trauma burn intensive care unit

Methicillin-resistant Staphylococcus aureus (MRSA) is an important pathogen causing health care-infections in the world, especially in burns. The aim of this study was to assess the extent of dissemination of MRSA isolated from burn patients in Burn Intensive Care Unit in Tunisia and to evaluate the frequency of virulence and antibiotics resistance genes. Among the 72 S. aureus isolates analyzed in the study, 54% were MRSA. The majority of MRSA (94.8%) were multidrug resistant and they had a high resistance rates to kanamycin (94.8%), tobramycin (90%), tetracycline (94.8%) and ciprofloxacin and rifampicin (87%, each). The gene aac(6')-Ie-aph(2″)-Ia conferring resistance to kanamycine and tobtamycin were detected in all isolates and the aph(3')-Ia gene conferring resistance to gentamicin were detected in 2.8% of resistant isolates. Tetracycline resistance genes tet(M), tet(K) and tet(L) were detected in 100%, 10.8% and 2.8% of the isolates, respectively. The SCCmec type III and the agr type I were the most predominant (69.2% and 90%, respectively). The 27 SCCmecIII-agrI isolates were clustered into two PFGE types A and B. The two representative isolates of PFGE clusters A and B belonged to ST239-t037 and ST241-t037 respectively. As conclusion, our results showed a high prevalence of MRSA in trauma burn intensive care unit belonging to two multidrug resistant clones ST239/ST241-agrI-t037-SCCmecIII MRSA. We also demonstrated that MRSA was disseminated between burn patients.

Lack of Direct Correlation between Biofilm Formation and Antimicrobial Resistance in Clinical Staphylococcus epidermidis Isolates from an Italian Hospital

Staphylococcus epidermidis is an opportunistic pathogen and a frequent cause of nosocomial infections. In this work, we show that, among 51 S. epidermidis isolates from an Italian hospital, only a minority displayed biofilm formation, regardless of their isolation source (peripheral blood, catheter, or skin wounds); however, among the biofilm-producing isolates, those from catheters were the most efficient in biofilm formation. Interestingly, most isolates including strong biofilm producers displayed production levels of PIA (polysaccharide intercellular adhesin), the main S. epidermidis extracellular polysaccharide, similar to reference S. epidermidis strains classified as non-biofilm formers, and much lower than those classified as intermediate or high biofilm formers, possibly suggesting that high levels of PIA production do not confer a particular advantage for clinical isolates. Finally, while for the reference S. epidermidis strains the biofilm production clearly correlated with the decreased sensitivity to antibiotics, in particular, protein synthesis inhibitors, in our clinical isolates, such positive correlation was limited to tetracycline. In contrast, we observed an inverse correlation between biofilm formation and the minimal inhibitory concentrations for levofloxacin and teicoplanin. In addition, in growth conditions favoring PIA production, the biofilm-forming isolates showed increased sensitivity to daptomycin, clindamycin, and erythromycin, with increased tolerance to the trimethoprim/sulfamethoxazole association. The lack of direct correlation between the biofilm production and increased tolerance to antibiotics in S. epidermidis isolates from a clinical setting would suggest, at least for some antimicrobials, the possible existence of a trade-off between the production of biofilm determinants and antibiotic resistance.

Comparative profiling of agr locus, virulence, and biofilm-production genes of human and ovine non-aureus staphylococci

Background

In a collaboration between animal and human health care professionals, we assessed the genetic characteristics shared by non-aureus staphylococci (NAS) infecting humans and dairy ewes to investigate their relatedness in a region concentrating half of the total National sheep stock. We examined by PCR 125 ovine and 70 human NAS for biofilm production, pyrogenic toxins, adhesins, autolysins genes, and accessory gene regulator (agr) locus. The microtiter plate assay (MPA) was used for the phenotypic screening of biofilm production. Ovine NAS included S. epidermidis, S. chromogenes, S. haemolyticus, S. simulans, S. caprae, S. warneri, S. saprophyticus, S. intermedius, and S. muscae. Human NAS included S. haemolyticus, S. epidermidis, S. hominis, S. lugdunensis, S. capitis, S. warneri, S. xylosus, S. pasteuri, and S. saprophyticus subsp. bovis.

Results

Phenotypically, 41 (32.8%) ovine and 24 (34.3%) human isolates were characterized as biofilm producers. Of the ovine isolates, 12 were classified as biofilm-producing while the remaining 29 as weak biofilm-producing. All 24 human isolates were considered weak biofilm-producing. Few S. epidermidis isolates harbored the icaA/D genes coding for the polysaccharide intercellular adhesin (PIA), while the bhp, aap, and embp genes coding biofilm accumulation proteins were present in both non-producing and biofilm-producing isolates. Fifty-nine sheep NAS (all S. epidermidis, 1 S. chromogenes, and 1 S. haemolyticus) and 27 human NAS (all S. epidermidis and 1 S. warneri) were positive for the agr locus: agr-3se (57.8%) followed by agr-1se (36.8%) predominated in sheep, while agr-1se (65.4%), followed by agr-2se (34.6%) predominated in humans.

Concerning virulence genes, 40, 39.2, 47.2%, 52.8, 80 and 43.2% of the sheep isolates carried atlE, aae, sdrF, sdrG, eno and epbS respectively, against 37.1, 42.8, 32.8, 60, 100 and 100% of human isolates. Enterotoxins and tsst were not detected.

Conclusions

Considerable variation in biofilm formation ability was observed among NAS isolates from ovine and human samples. S. epidermidis was the best biofilm producer with the highest prevalence of adhesin-encoding genes.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12917-022-03257-w.

Non-Native Peptides Capable of Pan-Activating the agr Quorum Sensing System across Multiple Specificity Groups of Staphylococcus epidermidis

Staphylococcus epidermidis is a leading cause of hospital-acquired infections. Traditional antibiotics have significantly reduced efficacy against this pathogen due to its ability to form biofilms on abiotic surfaces and drug resistance. The accessory gene regulator (agr) quorum sensing system is directly involved in S. epidermidis pathogenesis. Activation of agr is achieved via binding of the autoinducing peptide (AIP) signal to the extracellular sensor domain of its cognate receptor, AgrC. Divergent evolution has given rise to four agr specificity groups in S. epidermidis defined by the unique AIP sequence used by each group (AIPs-I-IV) with observed cross-group activities. As agr agonism has been shown to reduce biofilm growth in S. epidermidis, the development of pan-group activators of the agr system is of interest as a potential antivirulence strategy. To date, no synthetic compounds have been identified that are capable of appreciably activating the agr system of more than one specificity group of S. epidermidis or, to our knowledge, of any of the other Staphylococci. Here, we report the characterization of the structure-activity relationships for agr agonism by S. epidermidis AIP-II and AIP-III and the application of these new SAR data and those previously reported for AIP-I for the design and synthesis of the first multigroup agr agonists. These non-native peptides were capable of inducing the expression of critical biofilm dispersal agents (i.e., phenol-soluble modulins) in cell culture and represent new tools to study the role of quorum sensing in S. epidermidis infections.

Detection of the agr System and Resistance to Antimicrobials in Biofilm-Producing S. epidermidis

The ability of Staphylococcus epidermidis to produce virulence factors, such as biofilm, added to its increased resistance to antimicrobials can cause infections that are difficult to treat. Many staphylococcal virulence factors are under the control of the accessory gene regulator (agr). The objective of this study was to establish the agr locus and susceptibility of biofilm-producing S. epidermidis specimens to antimicrobial agents, through PCR reactions, reverse transcription polymerase chain reaction (RT-PCR), and the determination of minimum inhibitory concentration (MIC), and to analyze the clonal profile of 300 strains isolated from blood culture specimens from inpatients at a University Hospital in Brazil, over a 20-year period by pulsed-field gel electrophoresis (PFGE) and multilocus sequence typing (MLST) techniques. The ica operon expression was shown in 83.6% strains, bhp gene in 11.5%, and aap gene in 32.8%. Oxacillin resistance was detected in 90.1%, while 4.9% showed tigecycline resistance, and intermediate resistance to quinupristin/dalfopristin was identified in 0.4%. Clonal profile determination showed 11 clusters, with the ST2 type determined as the major cluster. The S. epidermidis biofilm producer demonstrated a predominance of agr I locus, oxacillin resistance, and SCCmec III as well as the potential dissemination of pathogenic clones in hospital settings over long periods.

Staphylococcus arlettae Genomics: Novel Insights on Candidate Antibiotic Resistance and Virulence Genes in an Emerging Opportunistic Pathogen

Coagulase Negative Staphylococci (CoNS) are becoming increasingly recognized as an important cause of human and animal infections. Notwithstanding their clinical relevance, annotation of genes potentially involved in pathogenicity and/or antibiotic resistance in the CoNS species Staphylococcus arlettae (SAR) is currently very limited. In the current work we describe the genome of a novel methicillin resistant isolate of SAR, which we named Bari, and present a comprehensive analysis of predicted antibiotic resistance profiles and virulence determinants for all the 22 currently available SAR genomes. By comparing predicted antibiotic resistance and virulence-associated genes with those obtained from a manual selection of 148 bacterial strains belonging to 14 different species of staphylococci and to two “outgroup” species, Bacillus subtilis (BS) and Macrococcus caseoliticus (MC), we derived some interesting observations concerning the types and number of antibiotic resistance-related and virulence-like genes in SAR. Interestingly, almost 50% of the putative antibiotic resistance determinants identified in this work, which include the clinically relevant mec, van, and cls genes, were shared among all the SAR strains herein considered (Bari included). Moreover, comparison of predicted antibiotic resistance profiles suggest that SAR is closely related to well-known pathogenic Staphylococcus species, such as Staphylococcus aureus (SA) and Staphylococcus epidermidis (SE). A similar analysis of predicted virulence factors, revealed that several genes associated with pathogenesis (including, for example, ica, nuc, and ssp), which are commonly found in the genomes of pathogenic staphylococci such as Staphylococcus haemolyticus (SH) and Staphylococcus saprophyticus (SS), are observed also in the SAR strains for which a genomic sequence is available. All in all, we believe that the analyses presented in the current study, by providing a consistent and comprehensive annotation of virulence and antibiotic resistance-related genes in SAR, can constitute a valuable resource for the study of molecular mechanisms of opportunistic pathogenicity in this species.

Emergence of community-acquired methicillin-resistant Staphylococcus aureus EMRSA-15 clone as the predominant cause of diabetic foot ulcer infections in Portugal

Methicillin-resistant Staphylococcus aureus (MRSA) are often found in infected diabetic foot ulcers, in which the prevalence may reach 40%. These complications are one of the main causes of morbidity in diabetic patients. The objectives of this study were to investigate the prevalence and antimicrobial resistance of MRSA strains in infected diabetic foot ulcers and to characterize their genetic lineages. Samples collected from 42 type 2 diabetic patients, presenting infected foot ulcers, were seeded onto ORSAB plates with 2 mg/L of oxacillin for MRSA isolation. Susceptibility to 14 antimicrobial agents was tested by the Kirby-Bauer disk diffusion method. The presence of resistance genes, virulence factors, and the immune evasion cluster system was studied by PCR. All isolates were characterized by MLST, accessory gene regulator (agr), spa, and staphylococcal chromosomal cassette mec (SCCmec) typing. Twenty-five MRSA strains were isolated. All isolates showed resistance to penicillin and cefoxitin. Sixteen isolates showed phenotypic resistance to erythromycin being 7 co-resistant to clindamycin. Resistance to trimethoprim-sulfamethoxazole was found in 2 isolates harboring the dfrA and dfrG genes. The IEC genes were detected in 80% of isolates, 16 of which were ascribed to IEC-type B. Isolates were assigned to 12 different spa types. The MLST analysis grouped the isolates into 7 sequence types being the majority (68%) ascribed to SCCmec type IV. In this study, there was a high prevalence of the EMRSA-15 clone presenting multiple resistances in diabetic foot ulcers making these infections complicated to treat leading to a higher morbidity and mortality in diabetic patients.

Differential Expression of the apsXRS System by Antimicrobial Peptide LL-37 in Commensal and Clinical Staphylococcus epidermidis Isolates

The three-component apsXRS system senses and responds to cationic antimicrobial peptides (CAMPs), which induces the expression of the dlt operon and the genes mprF and vrafG, modifying the surface net charge in Staphylococcus epidermidis, resulting in the repulsion of CAMPs. The apsXRS system has been only studied in the S. epidermidis 1457 strain, and there are no studies of prevalence and level of expression of apsXRS in commensal and clinical isolates. From 60 isolates, those selected from commensal healthy skin (n = 20), commensal healthy conjunctive (n = 10), and clinical ocular infection (n = 30) presented the apsX, apsR, and apsS genes in their genomes. Constitutive expression of apsX, apsR, and apsS genes was determined by RT-qPCR in all isolates. It was found that expression of apsX, apsR, and apsS was 3.3-5.9-fold higher in commensal isolates stimulated with LL-37 (15 µg/mL) than in clinical isolates. Similarly, expression of the dlt operon and the genes mprF, and vraFG was 8-10-fold higher in commensal isolates than in clinical. However, LL-37 did not increase the addition of lysine in the phospholipids of the cytoplasmic membrane in any of the isolates. Mutations in the apsS loop region, apsR, and their promoter sequence were not found. These results demonstrated that apsXRS system is essential in all isolates for its constitutive expression; however, LL-37 caused an increase of apsXRS expression in commensal isolates, suggesting that S. epidermidis isolates do not respond in the same way to the presence of LL-37.

Competition/antagonism associations of biofilm formation among Staphylococcus epidermidis Agr groups I, II, and III

Staphylococci have quorum-sensing (QS) systems that enable cell-to-cell communication, as well as the regulation of numerous colonization and virulence factors. The accessory gene regulator (Agr) operon is one of the Staphylococcus genus QS systems. Three groups (I, II, and III) are present in Staphylococcus epidermidis Agr operon. To date, it is unknown whether Agr groups can interact symbiotically during biofilm development. This study analyzed a symbiotic association among Agr groups during biofilm formation in clinical and commensal isolates. Different combinations among Agr group isolates was used to study biofilm formation in vitro and in vivo (using a mouse catheter-infection model). The analysis of Agr groups were also performed from samples of human skin (head, armpits, and nostrils). Different predominant coexistence was found within biofilms, suggesting symbiosis type. In vitro, Agr I had a competition with Agr II and Agr III. Agr II had a competition with Agr III, and Agr II was an antagonist to Agr I and III when the three strains were combined. In vivo, Agr II had a competition to Agr I, but Agr I and II were antagonists to Agr III. The associations found in vitro and in vivo were also found in different sites of the skin. Besides, other associations were observed: Agr III antagonized Agr I and II, and Agr III competed with Agr I and Agr II. These results suggest that, in S. epidermidis, a symbiotic association of competition and antagonism occurs among different Agr groups during biofilm formation.

Expression of superantigens and the agr system in Staphylococcus epidermidis

Infections with coagulase-negative staphylococci (CoNS) can involve the production of toxins such as superantigens, which contribute to tissue degradation and inflammatory immune responses. The accessory gene regulator (agr) quorum sensing system coordinates the expression of most S. aureus virulence factors. Therefore, the aim of this study was to investigate the expression of these superantigens and the presence of the agr locus in CoNS strains isolated from blood cultures. PCR was used to detect enterotoxin and agr genes and expression was analyzed by RT-PCR. Expression of the sea gene was observed in one S. epidermidis isolate andof sec-1 in two, seg and sei were expressed concomitantly in one isolate, and sei was expressed in another isolate. The agr group I was detected in S. epidermidis expressing the sea, seg and sei genes, whereas agr group II was detected in isolates expressing thesec-1 gene. The agr groups were only expressed in strains expressing thesec-1 gene. The results show that enterotoxin genes are highly frequent in CoNS isolated from clinical specimens and confirm the toxin-producing ability of these strains. The agr group II may be associated with enterotoxin C production by S. epidermidis, increasing the virulence of strains isolated from blood cultures and consequently the severity of sepsis caused by these organisms.

Limitations in the use of PSMγ, agr, RNAIII, and biofilm formation as biomarkers to define invasive Staphylococcus epidermidis from chronic biomedical device-associated infections

Staphylococcus epidermidis is a common cause of biomedical device-associated infections. Agr is the major quorum sensing system in staphylococci and regulates virulence factors. Four agr-specificity groups exist in S. epidermidis, and chronic S. epidermidis infections are hypothesised to select for agr-negative phenotypes. Therefore, we investigated S. epidermidis strains from prosthetic joint- and catheter-associated infections to establish i) whether an infection selects for an agr-negative phenotype; ii) the importance of PSMγ and iii) if the agr-specificity group is infection dependent. S. epidermidis nasal isolates from healthy volunteers were used as controls. The distribution of agr-specificity groups was significantly different between infection and control episodes, but did not distinguish between the infection types. PSMγ secretion was used to determine agr-activity and HPLC analysis showed that 44% of prosthetic and 32% of catheter-associated episodes produced no PSMγ in comparison to 8% of the control strains. However, PSMγ expression did not always correlate with RNAIII up-regulation, indicating that PSMγ synthesis is likely influenced by additional post-transcriptional control. The data suggests chronic S. epidermidis infections favour agr-specificity group 1 but the results suggest that they do not select for an agr-negative phenotype. Further studies are required to explore the mechanisms underlying the selection and survival of these S. epidermidis phenotypes isolated from biomedical device-associated infections.

Versatility of Biofilm Matrix Molecules in Staphylococcus epidermidis Clinical Isolates and Importance of Polysaccharide Intercellular Adhesin Expression during High Shear Stress

Staphylococcus epidermidis is a leading cause of infections related to biomaterials, mostly due to their ability to form biofilm. Biofilm accumulation mechanisms vary, including those that are dependent on specific proteins, environmental DNA (eDNA), or polysaccharide intercellular adhesin (PIA). We found that those isolates obtained from high-shear environments, such as the lumen of a catheter, are more likely to produce PIA-mediated biofilms than those isolates obtained from a low-shear biomaterial-related infection. This suggests that PIA functions as a mechanism that is protective against shear flow. Finally, we performed selection experiments documenting the heterogeneity of biofilm accumulation molecules that function in the absence of PIA, further documenting the biofilm-forming potential of S. epidermidis.

Staphylococcus epidermidis is a leading cause of hospital-associated infections, including those of intravascular catheters, cerebrospinal fluid shunts, and orthopedic implants. Multiple biofilm matrix molecules with heterogeneous characteristics have been identified, including proteinaceous, polysaccharide, and nucleic acid factors. Two of the best-studied components in S. epidermidis include accumulation-associated protein (Aap) and polysaccharide intercellular adhesin (PIA), produced by the enzymatic products of the icaADBC operon. Biofilm composition varies by strain as well as environmental conditions, and strains producing PIA-mediated biofilms are more robust. Clinically, biofilm-mediated infections occur in a variety of anatomical sites with diverse physiological properties. To test the hypothesis that matrix composition exhibits niche specificity, biofilm-related genetic and physical properties were compared between S. epidermidis strains isolated from high-shear and low-shear environments. Among a collection of 105 clinical strains, significantly more isolates from high-shear environments carried the icaADBC operon than did those from low-shear settings (43.9% versus 22.9%, P < 0.05), while there was no significant difference in the presence of aap (77.2% versus 75.0%, P > 0.05). Additionally, a significantly greater number of high-shear isolates were capable of forming biofilm in vitro in a microtiter assay (82.5% versus 45.8%, P < 0.0001). However, even among high-shear clinical isolates, less than half contained the icaADBC locus; therefore, we selected for ica-negative variants with increased attachment to abiotic surfaces to examine PIA-independent biofilm mechanisms. Sequencing of selected variants identified substitutions capable of enhancing biofilm formation in multiple genes, further highlighting the heterogeneity of S. epidermidis biofilm molecules and mechanisms.

IMPORTANCEStaphylococcus epidermidis is a leading cause of infections related to biomaterials, mostly due to their ability to form biofilm. Biofilm accumulation mechanisms vary, including those that are dependent on specific proteins, environmental DNA (eDNA), or polysaccharide intercellular adhesin (PIA). We found that those isolates obtained from high-shear environments, such as the lumen of a catheter, are more likely to produce PIA-mediated biofilms than those isolates obtained from a low-shear biomaterial-related infection. This suggests that PIA functions as a mechanism that is protective against shear flow. Finally, we performed selection experiments documenting the heterogeneity of biofilm accumulation molecules that function in the absence of PIA, further documenting the biofilm-forming potential of S. epidermidis.

Molecular and Phenotypic Characterization of Staphylococcus epidermidis Isolates from Healthy Conjunctiva and a Comparative Analysis with Isolates from Ocular Infection

Staphylococcus epidermidis is a common commensal of healthy conjunctiva and it can cause endophthalmitis, however its presence in conjunctivitis, keratitis and blepharitis is unknown. Molecular genotyping of S. epidermidis from healthy conjunctiva could provide information about the origin of the strains that infect the eye. In this paper two collections of S. epidermidis were used: one from ocular infection (n = 62), and another from healthy conjunctiva (n = 45). All isolates were genotyped by pulsed field gel electrophoresis (PFGE), multilocus sequence typing (MLST), staphylococcal cassette chromosome mec (SCCmec), detection of the genes icaA, icaD, IS256 and polymorphism type of agr locus. The phenotypic data included biofilm production and antibiotic resistance. The results displayed 61 PFGE types from 107 isolates and they were highly discriminatory. MLST analysis generated a total of 25 STs, of which 11 STs were distributed among the ocular infection isolates and lineage ST2 was the most frequent (48.4%), while 14 STs were present in the healthy conjunctiva isolates and lineage ST5 was the most abundant (24.4%). By means of a principal coordinates analysis (PCoA) and a discriminant analysis (DA) it was found that ocular infection isolates had as discriminant markers agr III or agr II, SCCmec V or SCCmec I, mecA gene, resistance to tobramycin, positive biofilm, and IS256⁺. In contrast to the healthy conjunctiva isolates, the discriminating markers were agr I, and resistance to chloramphenicol, ciprofloxacin, gatifloxacin and oxacillin. The discriminant biomarkers of ocular infection were examined in healthy conjunctiva isolates, and it was found that 3 healthy conjunctiva isolates [two with ST2 and another with ST9] (3/45, 6.66%) had similar genotypic and phenotypic characteristics to ocular infection isolates, therefore a small population from healthy conjunctiva could cause an ocular infection. These data suggest that the healthy conjunctiva isolates do not, in almost all cases, infect the eye due to their large genotypic and phenotypic difference with the ocular infection isolates.

Staphylococcus epidermidis agr quorum-sensing system: signal identification, cross talk, and importance in colonization

Staphylococcus epidermidis is an opportunistic pathogen that is one of the leading causes of medical device infections. Global regulators like the agr quorum-sensing system in this pathogen have received a limited amount of attention, leaving important questions unanswered. There are three agr types in S. epidermidis strains, but only one of the autoinducing peptide (AIP) signals has been identified (AIP-I), and cross talk between agr systems has not been tested. We structurally characterized all three AIP types using mass spectrometry and discovered that the AIP-II and AIP-III signals are 12 residues in length, making them the largest staphylococcal AIPs identified to date. S. epidermidis agr reporter strains were developed for each system, and we determined that cross-inhibitory interactions occur between the agr type I and II systems and between the agr type I and III systems. In contrast, no cross talk was observed between the type II and III systems. To further understand the outputs of the S. epidermidis agr system, an RNAIII mutant was constructed, and microarray studies revealed that exoenzymes (Ecp protease and Geh lipase) and low-molecular-weight toxins were downregulated in the mutant. Follow-up analysis of Ecp confirmed the RNAIII is required to induce protease activity and that agr cross talk modulates Ecp activity in a manner that mirrors the agr reporter results. Finally, we demonstrated that the agr system enhances skin colonization by S. epidermidis using a porcine model. This work expands our knowledge of S. epidermidis agr system function and will aid future studies on cell-cell communication in this important opportunistic pathogen.

Genetic determinants and biofilm formation of clinical Staphylococcus epidermidis isolates from blood cultures and indwelling devises

For a long time, Staphylococcus epidermidis, as a member of the coagulase-negative staphylococci, was considered as part of the physiological skin flora of the human being with no pathogenic significance. Today, we know that S. epidermidis is one of the most prevalent causes for implant-associated and nosocomial infections. We performed pheno- and genotypic analysis (ica, IS256, SCCmec types, agr groups) of biofilm formation in 200 isolates. Fifty percent were genetically ica-positive and produced biofilm. Among all studied isolates, agr II and III and SCCmec type I were the most prevalent, whereas within the selected multi-resistant isolates (29%), agr I and III and SCCmec type II dominated. SCCmec type I and mecA-negative S. epidermidis isolates were associated with agr II. The majority of the blood culture and biopsy isolates were assigned to agr III and SCCmec type I, whereas agr II was predominantly detected in mecA-negative S. epidermidis isolated from catheter and implant materials. MLST analysis revealed the major clonal lineages of ST2, ST5, ST10, and ST242 (total 13 STs). ST2 isolates from blood cultures were icaA/D-positive and harbored SCCmec types II and III and IS256, whereas the icaA/D- and IS256-positive ST23 isolates were assigned to SCCmec types I and IV.

Genome sequence of Staphylococcus arlettae strain CVD059, isolated from the blood of a cardiovascular disease patient

We have isolated a Staphylococcus arlettae strain, strain CVD059, from the blood of a rheumatic mitral stenosis patient. Here, we report the genome sequence and potential virulence factors of this clinical isolate. The draft genome of S. arlettae CVD059 is 2,565,675 bp long with a G+C content of 33.5%.

Comparison of Staphylococcus epidermidis isolated from prosthetic joint infections and commensal isolates in regard to antibiotic susceptibility, agr type, biofilm production, and epidemiology

Staphylococcus epidermidis is the predominant bacterial species in the normal flora of the human skin and superficial mucosal membranes. However, it has also emerged as the most important pathogen in infections related to foreign-body materials, such as prosthetic joints and heart valves. The aims of this study were to characterise S. epidermidis isolated from prosthetic joint infections (PJI; n=61) and commensal isolates from healthy individuals (n=24) in regard to antimicrobial sensitivity, agr type, hld gene presence, biofilm production including presence of ica and aap genes involved in the biofilm formation process and epidemiology using both phenotypic (the PhenePlate-system) and genotypic [multilocus sequence typing (MLST)] methods. Among the PJI isolates, the majority (67%) were multidrug-resistant. Two major clusters of PJI isolates could be identified; 44% belonged to MLST sequence type (ST) 2, all but one were of agr type 1, and 31% were assigned ST215 and were of agr type 3. Of the commensal isolates, only one isolate was multidrug-resistant, and they were more molecular epidemiologically diverse with mainly MLST singletons and a maximum of 3 isolates assigned to the identical ST. Biofilm production was detected in 41% of the PJI isolates and 58% of the commensal isolates, with the aap gene (95%) more frequently detected than the ica genes (62%) in the biofilm-positive isolates. In conclusion, S. epidermidis isolated from PJIs and commensal isolates differed regarding antimicrobial sensitivity and molecular epidemiological typing using MLST, but not substantially in the distribution of agr types, biofilm production, or the presence of ica and aap genes.

Staphylococcus epidermidis recovered from indwelling catheters exhibit enhanced biofilm dispersal and "self-renewal" through downregulation of agr

Background

In recent years, Staphylococcus epidermidis ( Se) has become a major nosocomial pathogen and the most common cause of infections of implanted prostheses and other indwelling devices. This is due in part to avid biofilm formation by Se on device surfaces. However, it still remains unknown that how the process of Se biofilm development is associated with relapsed infection in such patients.

Results

We have identified clinical Se isolates displaying enhanced biofilm dispersal and self-renewal relative to reference strain. These isolates also exhibit enhanced initial cell attachment, extracellular DNA release, cell autolysis and thicker microcolonies during biofilm development relative to reference strain. Our genetic analyses suggest that these clinical isolates exhibit significant downregulation of RNAIII, the effector molecule of the agr quorum sensing system, and upregulation of the autolysin gene atlE. Isogenic deletion of the agr system in Se 1457 confirmed that agr negatively regulating atlE resulted in enhanced initial cell attachment, extracellular DNA release, cell autolysis and biofilm formation abilities. In contrast, double deletion of agr and atlE significantly abolished these features.

Conclusions

Collectively, these data reveal the role of agr system in long-term biofilm development and pathogenesis during Se caused indwelling devices-related relapsed infection.

Pseudomonas aeruginosa extracellular products inhibit staphylococcal growth, and disrupt established biofilms produced by Staphylococcus epidermidis

Multiple bacterial species often coexist as communities, and compete for environmental resources. Here, we describe how an opportunistic pathogen, Pseudomonas aeruginosa, uses extracellular products to interact with the nosocomial pathogen Staphylococcus epidermidis. S. epidermidis biofilms and planktonic cultures were challenged with P. aeruginosa supernatant cultures overnight. Results indicated that quorum-sensing-controlled factors from P. aeruginosa supernatant inhibited S. epidermidis growth in planktonic cultures. We also found that P. aeruginosa extracellular products, mainly polysaccharides, disrupted established S. epidermidis biofilms. Cellulase-treated P. aeruginosa supernatant, and supernatant from pelA, pslF and pelApslBCD mutants, which are deficient in polysaccharide biosynthesis, diminished the disruption of S. epidermidis biofilms. In contrast, S. epidermidis supernatant in overnight cultures had no effect on established P. aeruginosa biofilms and planktonic growth. These findings reveal that P. aeruginosa extracellular products are important microbial competition factors that overcome competition with S. epidermidis, and the results may provide clues for the development of a novel strategy for controlling S. epidermidis biofilms.

Understanding the physiology and adaptation of staphylococci: A post-genomic approach

Staphylococcus aureus as well as coagulase-negative staphylococci are medically highly important pathogens characterized by an increasing resistance rate toward many antibiotics. Although normally being skin and mucosa commensals, some staphylococcal species and strains have the capacity to cause a wide range of infectious diseases. Many of these infections affect immunocompromised patients in hospitals. However, community-acquired staphylococcal infections due to resistant strains are also currently on the rise. In the light of this development, there is an urgent need for novel anti-staphylococcal therapeutic and prevention strategies for which a better understanding of the physiology of these bacteria is an essential prerequisite. Within the past years, staphylococci have been in the focus of genomic research, resulting in the determination and publication of a range of full-genome sequences of different staphylococcal species and strains which provided the basis for the design and application of DNA microarrays and other genomic tools. Here we summarize the results of the project group 'Staphylococci' within the research network 'Pathogenomics' giving new insights into the genome structure, molecular epidemiology, physiology, and genetic adaptation of both S. aureus and coagulase-negative staphylococci.

Impact of the accessory gene regulatory system (Agr) on extracellular proteins, codY expression and amino acid metabolism in Staphylococcus epidermidis

The quorum-sensing system Agr is part of a complex regulatory network of gene expression in staphylococci. This study presents the effect of an agr mutation on a biofilm-forming Staphylococcus epidermidis isolate by employing proteome and transcriptome analysis. The agr mutant exhibited a significantly lowered amount of extracellular proteins: amongst others SspA, AtlE, GehD and the phenol soluble modulins PSM1/2. Cytoplasmic proteome analysis and expression profiling indicated that the agr inactivation led to a strongly altered regulation of metabolism and virulence. Most strikingly, expression of CodY, a global regulator of virulence and stationary phase gene expression, was decreased in the agr mutant. In this respect, homologous genes known to be controlled by CodY in Bacillus subtilis and Lactococcus lactis were found to be up-regulated in the S. epidermidis agr mutant. The combined data show that wild-type and agr mutant differ with respect to amino acid biosynthesis and oligopeptide transport, carbohydrate utilization, as well as GMP and IMP interconversion. Due to the varying physiological properties S. epidermidis agr mutants, which often occur spontaneously, might be capable of colonizing alternative ecological niches in the human host and could, therefore, have an advantage in adapting to changing environmental conditions.