[Spider bite or infection caused by Panton Valentine leucocidin-producing Staphylococcusaureus?] / Morsure d'araignée ou infection à Staphylococcusaureus producteur de toxine de Panton Valentine ?

INTRODUCTION: Spiders, especially those of the genus Loxoceles such as L. rufescens, endemic in Mediterranean regions, are frequently reported as causes of venom poisoning in humans in the south of France. The most common signs consist of cutaneous necrosis presenting initially as inflammatory cellulitis and progressing towards the emergence of a necrotic centre. PATIENTS AND METHODS: We report 4 cases, initially considered as spider bites due to their sudden occurrence and pain. Rigorous clinical examination coupled with collection of samples for laboratory analysis ultimately enabled the diagnosis to be corrected to one of suppurative skin infection caused by Staphylococcusaureus producing the cytotoxin Panton Valentine leucocidin. DISCUSSION: These observations highlight the potential for confusion between spider bites and infections with PVL-producing S. aureus.

Time to blood culture positivity: An independent predictor of infective endocarditis and mortality in patients with Staphylococcus aureus bacteraemia.

OBJECTIVES: Time to blood culture positivity (TTP), a routinely available parameter in automated blood culture systems, may be a proxy for infectious burden in patients with bloodstream infections. We aimed to study the association between TTP and infective endocarditis (IE), or death, in patients with Staphylococcus aureus bacteraemia. METHODS: VIRSTA is a multicentre prospective cohort study that included all adult patients with S. aureus bacteraemia in eight university hospitals in France (2009-2011). We analysed data from four centres which collected data on TTP. Regression models were used to study the association between TTP and definite IE (Duke-Li criteria), and 30 day-mortality. RESULTS: We included 587 patients with S. aureus bacteraemia: mean age was 65.3 ± 16.3 years, 420 out of 587 patients (71.6%) were male, 121 out of 587 (20.6%) died, and 42 out of 587 (7.2%) had definite IE. Median TTP of first positive blood culture was 13.7 h (interquartile range 9.9-18). On multivariate analysis, 30-day mortality was associated with TTP ≤13.7 h (74/295 (25.1%) vs. 47/292 (16.1%), p 0.02), as well as old age, McCabe score, methicillin resistance, stroke, pneumonia, and C-reactive protein. TTP was also independently associated with IE, but with a U-shape curve: IE was more common in the first (TTP <10 h, 17/148, 11.5%), and the last (TTP ≥18 h, 8/146, 5.5%) quartiles of TTP, p 0.002. CONCLUSIONS: TTP provides reliable information in patients with S. aureus bacteraemia, on the risk of IE, and prognosis, with short TTP being an independent predictor of death. These data, readily available at no cost, may be used to identify patients who require specific attention.

Identification of a PVL-negative SCCmec-IVa sublineage of the methicillin-resistant Staphylococcus aureus CC80 lineage: understanding the clonal origin of CA-MRSA.

OBJECTIVES: Community-acquired (CA) methicillin-resistant Staphylococcus aureus (MRSA) isolates belonging to clonal complex 80 (CC80) are recognized as the European CA-MRSA. The prevailing European CA-MRSA clone carries a type IVc staphylococcal cassette chromosome mec (SCCmec) and expresses Panton-Valentine leukocidin (PVL). Recently, a significant increase of PVL-negative CC80 MRSA has been observed in Denmark. The aim of this study was to examine their genetics and epidemiology, and to compare them to the European CA-MRSA clone in order to understand the emergence of PVL-negative CC80 MRSA. METHODS: Phylogenetic analysis of the CC80 S. aureus lineage was conducted from whole-genome sequences of 217 isolates (23 methicillin-susceptible S. aureus and 194 MRSA) from 22 countries. All isolates were further genetically characterized in regard to resistance determinants and PVL carriage, and epidemiologic data were obtained for selected isolates. RESULTS: Phylogenetic analysis revealed the existence of three distinct clades of the CC80 lineage: (a) an methicillin-susceptible S. aureus clade encompassing Sub-Saharan African isolates (n = 13); (b) a derived clade encompassing the European CA-MRSA SCCmec-IVc clone (n = 185); and (c) a novel and genetically distinct clade encompassing MRSA SCCmec-IVa isolates (n = 19). All isolates in the novel clade were PVL negative, but carried remnant parts (8-12 kb) of the PVL-encoding prophage ΦSa2 and were susceptible to fusidic acid and kanamycin/amikacin. Geospatial mapping could link these isolates to regions in the Middle East, Asia and South Pacific. CONCLUSIONS: This study reports the emergence of a novel CC80 CA-MRSA sublineage, showing that the CC80 lineage is more diverse than previously assumed.

Vancomycin treatment is a risk factor for vancomycin-nonsusceptible Staphylococcus capitis sepsis in preterm neonates.

OBJECTIVES: Multidrug-resistant, vancomycin-nonsusceptible Staphylococcus capitis is an emerging cause worldwide of late-onset sepsis (LOS) in preterm neonates. The pathophysiology and risk factors for S. capitis-related LOS are poorly understood, but we hypothesized that S. capitis LOS follows translocation from the gut microbiota rather than catheter invasion. The objective of this study was to investigate the risk factors of S. capitis LOS and gut colonization. METHODS: We conducted a prospective single-centre cohort study of patients hospitalized in a tertiary-care unit (Lyon, France) from June 2011 to January 2012. S. capitis gut colonization was determined weekly from stool cultures. The determinants of gut colonization and LOS were established by multivariate Cox proportional hazards models. RESULTS: Eighty-three (36.2%) of 229 patients had S. capitis-positive stool culture, and 28 (12.2%) developed S. capitis LOS during hospitalization. Independent risk factors for S. capitis LOS included prior administration of vancomycin independent of a previous LOS episode (hazard ratio 6.44, 95% confidence interval 2.15-19.3, p 0.001) and low birth weight (hazard ratio 0.72 per 100 g increase, 95% confidence interval 0.55-0.95, p 0.02). The prior administration of vancomycin was also an independent risk factor for S. capitis colonization (hazard ratio 3.45, 95% confidence interval 2.07-5.76, p <0.001), particularly in the first week of life and in noncolonized neonates. CONCLUSIONS: Neonates treated with vancomycin are at a higher risk of LOS caused by vancomycin-nonsusceptible S. capitis. The use of vancomycin in neonates must urgently be optimized to limit the selection of vancomycin-nonsusceptible strains, for which alternative antibiotics are lacking.

MRSA infections among patients in the emergency department: a European multicentre study.

BACKGROUND: MRSA is a therapeutic concern worldwide, and a major agent of community-acquired skin and soft tissue infections (CA-SSTIs). While the US epidemiology of MRSA in CA-SSTIs is well described and reports the high prevalence of the USA300 clone, data on the European situation are lacking. OBJECTIVES: To determine the prevalence and clonal characteristics of MRSA in CA-SSTIs in seven European emergency departments. PATIENTS AND METHODS: From April to June 2015, patients presenting to the tertiary hospital emergency department with a Staphylococcus aureus CA-SSTI were prospectively enrolled. S. aureus isolates were characterized by antimicrobial susceptibility testing, detection of Panton-Valentine leucocidin encoding genes and spa-typing, MLST and/or DNA microarray. RESULTS: Two-hundred and five cases of S. aureus-associated CA-SSTIs were included, comprising folliculitis, furuncles, abscesses, paronychia, impetigo, carbuncles and cellulitis. Of the 205 cases, we report an MRSA prevalence rate of 15.1%, with a north (0%) to south (29%) increasing gradient. Fifty-one isolates were Panton-Valentine leucocidin-positive (24.9%), whether MSSA or MRSA, with a heterogeneous distribution between countries. Clonal distribution of MSSA and MRSA showed high diversity, with no predominant circulating clone and no archetypical USA300 CA-MRSA clone. CONCLUSIONS: This original prospective multicentre study highlights stark differences in European MRSA epidemiology compared with the USA, and that the USA300 CA-MRSA clone is not predominant among community-infected patients in Europe.

Emergence and dissemination of a linezolid-resistant Staphylococcus capitis clone in Europe.

Objectives: We investigated the epidemiological, clinical, microbiological and genetic characteristics of linezolid-resistant (LZR) Staphylococcus capitis isolates from French ICUs, and compared them with LZR S. capitis isolates from other European countries. Methods: All LZR isolates were subjected to antimicrobial susceptibility testing (AST) and the presence of cfr and optrA genes as well as mutations in the 23S rRNA and ribosomal proteins were investigated using specific PCR with sequencing. The genetic relationship between isolates was investigated using PFGE and WGS. Epidemiological data concerning LZR S. capitis were collected retrospectively in French microbiology laboratories. Results: Twenty-one LZR isolates were studied: 9 from France, 11 from Greece and 1 from Finland. All were resistant to methicillin and aminoglycosides. In addition, this unusual AST profile was identified in S. capitis isolates from seven French hospitals, and represented up to 12% of the S. capitis isolates in one centre. A G2576T mutation in 23S rRNA was identified in all isolates; cfr and optrA genes were absent. All isolates belonged to the same clone on the basis of their PFGE profiles, whatever their geographical origin. WGS found at most 212 SNPs between core genomes of the LZR isolates. Conclusions: We identified and characterized an LZR S. capitis clone disseminated in three European countries, harbouring the same multiple resistance and a G2576T mutation in the 23S rRNA. The possible unrecognized wider distribution of this clone, belonging to a species classically regarded as a low-virulence skin colonizer, is of major concern not least because of the increasing use of oxazolidinones.

In vitro activity of ceftobiprole on 440 Staphylococcus aureus strains isolated from bronchopulmonary infections.

OBJECTIVE: We assessed the in vitro activity of ceftobiprole on 440 Staphylococcus aureus clinical strains isolated from bronchopulmonary infections (2010-2014). METHODS: S. aureus isolates were characterized for methicillin resistance, PVL status, and clonal complex. All isolates were tested for minimal inhibitory concentrations (MIC) determination by broth microdilution method for ceftobiprole, ceftaroline fosamil, and comparator antibiotics (linezolid, tigecycline, vancomycin, and daptomycin). RESULTS: A total of 325 (74%) strains were methicillin-susceptible S. aureus (MSSA) and 115 (26%) were methicillin-resistant S. aureus (MRSA); 105 (24%) S. aureus strains were PVL-positive, including 35.2% (37/105) MRSA and 64.8% (68/105) MSSA. Ceftobiprole was highly active against S. aureus with MIC90 of 1 mg/L, MICs ranging between 0.12 and 4mg/L (only one resistant strain, MIC of 4 mg/L). MIC50 and MIC90 were twice lower in MSSA than MRSA. Moreover, PVL+ MRSA were slightly more susceptible to ceftobiprole (MIC50 of 0.5 mg/L and MIC90 of 1 mg/L) than PVL- MRSA (MIC50 and MIC90 of 1 mg/L). The ceftobiprole-resistant strain was also resistant to ceftaroline fosamil and presented the D239L mutation in PBP2A. The comparator antibiotics were equally active on the strains tested, with MIC90 of 0.5 mg/L for ceftaroline fosamil, tigecycline, and daptomycin; 1 mg/L for vancomycin; and 2 mg/L for linezolid. CONCLUSIONS: Our results suggest that ceftobiprole is highly active against S. aureus and is an effective alternative to vancomycin or linezolid in the management of staphylococcal pneumonia. However, close monitoring of isolates should be maintained to prevent resistant strain diffusion.

Does bacteriology laboratory automation reduce time to results and increase quality management?

Due to reductions in financial and human resources, many microbiological laboratories have merged to build very large clinical microbiology laboratories, which allow the use of fully automated laboratory instruments. For clinical chemistry and haematology, automation has reduced the time to results and improved the management of laboratory quality. The aim of this review was to examine whether fully automated laboratory instruments for microbiology can reduce time to results and impact quality management. This study focused on solutions that are currently available, including the BD Kiestra™ Work Cell Automation and Total Lab Automation and the Copan WASPLab(®).

Wide geographical dissemination of the multiresistant Staphylococcus capitis NRCS-A clone in neonatal intensive-care units.

Nosocomial late-onset sepsis represents a frequent cause of morbidity and mortality in preterm neonates. The Staphylococcus capitis clone NRCS-A has been previously described as an emerging cause of nosocomial bacteraemia in French neonatal intensive-care units (NICUs). In this study, we aimed to explore the possible unrecognized dissemination of this clone on a larger geographical scale. One hundred methicillin-resistant S. capitis strains isolated from neonates (n = 86) and adult patients (n = 14) between 2000 and 2013 in four different countries (France, Belgium, the UK, and Australia) were analysed with SmaI pulsed-field gel electrophoresis (PFGE) and dru typing. The vast majority of NICU strains showed the NRCS-A pulsotype and the dt11c type (96%). We then randomly selected 14 isolates (from neonates, n = 12, three per country; from adult patients, n = 2), considered to be a subset of representative isolates, and performed further molecular typing (SacII PFGE, SCCmec typing, and multilocus sequence typing-like analysis), confirming the clonality of the S. capitis strains isolated from neonates, despite their distant geographical origin. Whole genome single-nucleotide polymorphism-based phylogenetic analysis of five NICU isolates (from the different countries) attested to high genetic relatedness within the NRCS-A clone. Finally, all of the NRCS-A strains showed multidrug resistance (e.g. methicillin and aminoglycoside resistance, and decreased vancomycin susceptibility), with potential therapeutic implications for infected neonates. In conclusion, this study represents the first report of clonal dissemination of methicillin-resistant coagulase-negative Staphylococcus clone on a large geographical scale. Questions remain regarding the origin and means of international spread, and the reasons for this clone's apparent predilection for neonates.

Adaptation to vancomycin pressure of multiresistant Staphylococcus capitis NRCS-A involved in neonatal sepsis.

OBJECTIVES: The Staphylococcus capitis clone NRCS-A has recently been described as a frequent cause of late-onset sepsis (LOS) in pre-term neonates worldwide. Representatives of this clone exhibit non-susceptibility to vancomycin, the first-line agent used in LOS. Cases of prolonged S. capitis LOS despite vancomycin treatment have been reported. We investigated whether NRCS-A strains exhibit faster adaptation to vancomycin pressure as compared with other staphylococci. METHODS: Strains of S. capitis NRCS-A, S. capitis non-NRCS-A and Staphylococcus epidermidis (n = 2 each, all with vancomycin MICs ≤2 mg/L) and the prototype vancomycin-heteroresistant Staphylococcus aureus Mu3 were subcultured daily for 15 days with 0.25-32 mg/L vancomycin. Regression coefficients of daily log2 MICs on time were used to estimate the kinetics of resistance development. Changes in bacterial cell-wall thickness were measured by transmission electron microscopy. To assess the stability of resistance and the emergence of cross-resistance, vancomycin, teicoplanin, daptomycin and linezolid MICs were measured before and after vancomycin treatment, as well as after nine additional subcultures without antibiotics. RESULTS: All strains developed a stable resistance to vancomycin, but this occurred significantly faster in S. capitis NRCS-A than in S. capitis non-NRCS-A (P < 0.001) and other species (P < 0.0001). Vancomycin resistance in S. capitis NRCS-A was associated with significant cell-wall thickening and an increase in MICs of daptomycin and teicoplanin, but not linezolid. CONCLUSIONS: S. capitis NRCS-A rapidly adapts to vancomycin pressure as compared with potential niche competitors, a feature that might contribute to its success in neonatal ICUs where vancomycin is widely prescribed.

Evaluation of the R-Biopharm RIDA®GENE Panton-Valentine leukocidin (PVL) kit for the detection of Staphylococcus aureus PVL from pus samples.

Staphylococcus aureus Panton-Valentine leukocidin (PVL) is associated with primary skin and soft-tissue infections (SSTI). We aimed to divert the RIDA®GENE PVL kit (RBiopharm) from its intended use on cultures to the detection of PVL-encoding genes directly from pus samples. Performance was compared with that of the in-house PCR method developed by the French National Reference Centre for Staphylococci. From June 2013 to May 2014, pus samples from S. aureus SSTI were tested. Our in-house PCR was performed on parallel cultures as the gold standard, while the RIDA®GENE PVL assay was used directly on pus samples from the sterile container, or a swab or an Eswab previously dipped in the pus. The kit specificity was also evaluated with pus samples that grew Streptococcus pyogenes. S. aureus reference strains harboring PVL-encoding genes, including known polymorphisms, were also tested. A total of 56 S. aureus-containing pus samples (28 PVL + and 28 PVL-) were collected and analyzed. Sensitivity and specificity of the commercial kit were 96.4 % and 100 % respectively, with equal performance whether tested directly from the sterile container or the Eswab. Sensitivity was lower (67.9 %) when the test was performed from a regular SSTI swab. None of the Streptococcus pyogenes pus samples scored positive (n = 5). Specificity was assessed using reference strains (n = 14); in all strains the PVL gene was correctly detected. This study identified the RIDA®GENE PVL kit as an efficient, sensitive, and specific tool for the rapid detection of PVL-encoding genes in pus samples.

Comparison of Sofia Legionella FIA and BinaxNOW® Legionella urinary antigen card in two national reference centers.

The Sofia Legionella Fluorescence Immunoassay (FIA; Quidel) is a recently introduced rapid immunochromatographic diagnostic test for Legionnaires' disease using immunofluorescence technology designed to enhance its sensitivity. The aim of this study was to evaluate its performance for the detection of urinary antigens for Legionella pneumophila serogroup 1 in two National Reference Centers for Legionella. The sensitivity and specificity of the Sofia Legionella FIA test were determined in concentrated and nonconcentrated urine samples, before and after boiling, in comparison with the BinaxNOW® Legionella Urinary Antigen Card (UAC; Alere). Compared with BinaxNOW® Legionella UAC, the sensitivity of the Sofia Legionella test was slightly higher in nonconcentrated urine samples and was identical in concentrated urine samples. The specificity of the Sofia Legionella FIA test was highly reduced by the concentration of urine samples. In nonconcentrated samples, a lack of specificity was observed in 2.3 % of samples, all of them resolved by heat treatment. The Sofia Legionella FIA is a sensitive test for detecting Legionella urinary antigens with no previous urine concentration. However, all positive samples have to be re-tested after boiling to reach a high specificity. The reading is automatized on the Sofia analyzer, which can be connected to laboratory information systems, facilitating accurate and rapid reporting of results.

Community-acquired infections due to Staphylococcus argenteus lineage isolates harbouring the Panton-Valentine leucocidin, France, 2014.

We describe two cases of human infections caused by Staphylococcus aureus clonal complex (CC) 75, also called Staphylococcus argenteus, harbouring the Panton-Valentine leucocidin (PVL). These two sporadic cases were community-acquired, and identified in France in 2014. Both had an epidemiological link with Mayotte, an overseas department of France located in the Indian Ocean off the south-eastern African coast. This report illustrates that, contrary to previous descriptions, S. argenteus can acquire important virulence factors and be responsible for severe infections.

α-Defensins partially protect human neutrophils against Panton-Valentine leukocidin produced by Staphylococcus aureus.

UNLABELLED: α-Defensins produced by neutrophils are important effector molecules of the innate immune system. In addition to their microbicidal effects, α-defensins have the ability to neutralize bacterial toxins. Panton-Valentine leukocidin (PVL) is the hallmark of community-acquired methicillin-resistant Staphylococcus aureus. Staphylococcus aureus that produce PVL are responsible for severe diseases, including necrotizing pneumonia. Polymorphonuclear neutrophils (PMNs) are the target cells of PVL action. The goal of this study was to elucidate the effect of a group of α-defensins known as the human neutrophil peptides (HNPs) on the interactions between LukS-PV and LukF-PV, which compose PVL, and human PMNs. We observed that HNPs bound to both subunits of PVL and significantly decreased PVL pore formation in PMNs, with a maximum inhibition of 27%. When various HNP molecules were tested individually under the same conditions, we observed that HNP3, but not HNP1 or 2, decreased pore formation. Similarly, HNP3 significantly decreased PVL-induced PMN lysis, with a maximum inhibition of 31%. Interestingly, HNPs did not affect LukS-PV LukF-PV oligomerization, LukS-PV LukF-PV binding to PMNs or calcium influx induced by PVL in PMNs. Our results suggest that HNP3 partially protects neutrophils against PVL by interfering with the conformational changes of PVL required to form a functional pore. SIGNIFICANCE AND IMPACT OF THE STUDY: Panton-Valentine leukocidin (PVL) is a pore-forming toxin produced by Staphylococcus aureus, responsible for neutrophil damage and key player of severe staphylococcal diseases. Antimicrobial peptides produced by neutrophils (HNP1-3) neutralize several other bacterial cytotoxins. We examined the impact of human neutrophil peptides (HNPs) on PVL cytotoxicity against human neutrophils and we found that HNPs bind to both LukS and LukF components of PVL, thereby inhibiting pore formation and neutrophil lysis. Our results suggest that HNP3 may impair PVL conformational changes required to form a functional pore and provide insight into the pathogenesis of PVL-related staphylococcal infection, with potential impact on the disease outcome.

Delta-toxin production deficiency in Staphylococcus aureus: a diagnostic marker of bone and joint infection chronicity linked with osteoblast invasion and biofilm formation.

Biofilm formation, intra-osteoblastic persistence, small-colony variants (SCVs) and the dysregulation of agr, the major virulence regulon, are possibly involved in staphylococcal bone and joint infection (BJI) pathogenesis. We aimed to investigate the contributions of these mechanisms among a collection of 95 Staphylococcus aureus clinical isolates from 64 acute (67.4%) and 31 chronic (32.6%) first episodes of BJI. The included isolates were compared for internalization rate, cell damage and SCV intracellular emergence using an ex vivo model of human osteoblast infection. Biofilm formation was assessed in a microbead immobilization assay (BioFilm Ring test). Virulence gene profiles were assessed by DNA microarray. Seventeen different clonal complexes were identified among the screened collection. The staphylococcal internalization rate in osteoblasts was significantly higher for chronic than acute BJI isolates, regardless of the genetic background. Conversely, no differences regarding cytotoxicity, SCV emergence, biofilm formation and virulence gene distribution were observed. Additionally, agr dysfunction, detected by the lack of delta-toxin production using whole-cell matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) analysis (n = 15; 15.8%), was significantly associated with BJI chronicity, osteoblast invasion and biofilm formation. These findings provide new insights into MSSA BJI pathogenesis, suggesting the correlation between chronicity and staphylococcal osteoblast invasion. This adaptive mechanism, along with biofilm formation, is associated with agr dysfunction, which can be routinely assessed by delta-toxin detection using MALDI-TOF spectrum analysis, possibly providing clinicians with a diagnostic marker of BJI chronicity at the time of diagnosis.

Correlation between clinical data and antibiotic resistance in coagulase-negative Staphylococcus species isolated from 68 patients with acute post-cataract endophthalmitis.

Coagulase-negative staphylococci (CNS) cause the majority of post-cataract endophthalmitis, which can lead to anatomical and/or functional loss of the eye. This study reports the antibiotic susceptibilities of CNS isolates associated with acute post-cataract endophthalmitis cases and correlates antibiotic resistance with severity and outcome of infection in these patients. Clinical data (initial ocular examination, final prognosis, antibiotic treatment) and the antibiotic susceptibilities of the isolated CNS strains were obtained from 68 patients with post-surgical endophthalmitis recruited during a 7-year period by the FRench Institutional ENDophthalmitis Study (FRIENDS) group. The CNS strains displayed 100% susceptibility to vancomycin, 70% to fluoroquinolones, 83% to fosfomycin, 46% to imipenem and 18% to piperacillin. The most effective antibiotic combinations were fosfomycin plus a fluoroquinolone and imipenem plus a fluoroquinolone, which were considered adequate in 80% and 58% of patients, respectively. Methicillin resistance was significantly associated with older age (p 0.001), diabetes mellitus (p 0.004), absence of fundus visibility (p 0.06), and poor visual prognosis (p 0.03). Resistance to fluoroquinolones was significantly associated with absence of fundus visibility (p 0.05) and diabetes mellitus (p 0.02). This large prospective study demonstrates that methicillin resistance and, to a lesser extent, fluoroquinolone resistance in CNS strains causing postoperative endophthalmitis are both prevalent in France and associated with a poorer visual prognosis. These results emphasize the need for an effective surveillance of this antibiotic resistance and the development of new diagnostic tools for rapid detection for early optimization of antibiotic therapy in endophthalmitis patients.

The levels of antibodies to Panton-Valentine leukocidin (PVL) vary with PVL prevalence along a north-to-south gradient.

Recent research on Staphylococcus aureus vaccine development has focused on active immunization against Panton-Valentine leukocidin (PVL), a potent leukotoxin associated with both superficial and severe deep-seated infections. PVL prevalence is highly variable worldwide, but it is unknown to what extent immunity to PVL varies between patients from geographic areas with different PVL-positive S. aureus prevalences. We conducted a retrospective multicentric study of anti-PVL and anti-alpha-toxin (Hla) antibody levels in uninfected adult patients from France (low PVL prevalence; n = 200), Algeria (moderate prevalence; n = 143), and Senegal (high prevalence; n = 228). The antibody levels were quantified by an enzyme-linked immunosorbent assay (ELISA) procedure. Because Hla is present in virtually all S. aureus strains, its corresponding antibody levels were considered to reflect population exposure to S. aureus. Compared with French participants, the average anti-PVL antibody levels were 2.5-fold and 8.2-fold higher in Algerian and Senegalese participants, respectively (p < 0.001). Conversely, anti-Hla antibody levels did not differ between participants from the three countries, suggesting that the observed differences in anti-PVL antibody levels were not biased by variations in population exposure to S. aureus. Hence, anti-PVL antibody levels in the general populations of France, Algeria, and Senegal vary widely and match variations in PVL-positive S. aureus strain prevalence, with an increasing north-to-south gradient. To conclude, immunity to PVL in a given population correlates with local PVL prevalence. This finding can help to inform PVL vaccine strategies.

The incidence of Staphylococcus aureus ST8-USA300 among French pediatric inpatients is rising.

Methicillin-resistant Staphylococcus aureus (MRSA) formerly colonized and infected only inpatients in hospitals, but have been reported in community settings worldwide over the last 20 years. In France, the prevalence of such MRSA remains low and outbreaks have, until now, been mainly due to the ST80 clone. However, there were two outbreaks of MRSA clone ST-USA300 recently in France, including one involving children. To investigate epidemiological developments, we studied the 77 MRSA isolated from pediatric patients hospitalized between 2008 and 2013 in three French hospitals. The median incidence of MRSA was stable and low (0.137 per 100 admissions). The prevalence of Panton-Valentine leukocidin (PVL)-positive MRSA was high (33.8 %). The 26 PVL-positive MRSA were genetically diverse, with two clones being predominant: ST80 (12 isolates, 46.1 %) and ST8-USA300 (8 isolates, 30.8 %). The incidence of ST8-USA300 increased over the 6-year period. We believe that screening for ST8-USA300 should be improved: medical biologists should be encouraged to search for PVL genes in all MRSA isolates recovered from abscesses, whatever the susceptibility pattern of the isolate, and not only when suggestive of ST80.

Community-acquired meticillin-resistant Staphylococcus aureus strain USA300 resists staphylococcal protein A modulation by antibiotics and antimicrobial peptides.

Community-acquired meticillin-resistant Staphylococcus aureus (CA-MRSA) causes severe diseases through virulence factors such as staphylococcal protein A (SpA), which favours immune evasion. We have previously shown that antimicrobial peptides (AMPs) and antibiotics decrease SpA expression in CA-MRSA strains. Here we examined the effects of antibiotics and AMPs, alone and in combination, on SpA expression in various CA-MRSA strains. Six S. aureus isolates corresponding to the major worldwide CA-MRSA clones (ST8-USA300, ST80 and ST30) were selected. Strains were cultured to exponential growth phase and were subsequently incubated with antibiotics (tigecycline, linezolid, clindamycin and vancomycin) at 0.25× MIC or with AMPs [human neutrophil peptide (HNP)-1-3] at the LD50, alone and in combination. After 6h, cultures were assessed for spa mRNA by RT-PCR, whilst SpA protein was measured by specific ELISA after 18h. When used alone, antibiotics (clindamycin, linezolid and tigecycline) or HNPs significantly reduced both SpA production and mRNA levels in ST30 and ST80 strains. When used in combination, HNPs and clindamycin, linezolid or tigecycline synergistically reduced SpA production (6-100-fold) and spa mRNA levels (4-20-fold) in ST80 and ST30 strains. In contrast, for USA300 strains, among all antibiotics, clindamycin alone reduced SpA production (3.5-fold), whereas with combined treatments including HNPs, only a slight reduction in SpA production (1.7-2.2-fold) was observed. In conclusion, antibiotics and AMPs do not modulate SpA expression in USA300, unlike in other CA-MRSA clones. This observation suggests that the virulence and successful spread of USA300 strains is associated with a specific regulatory network.