Panton-Valentine leukocidin (PVL) is a cytotoxin that causes leukocyte destruction and tissue necrosis. It is produced by fewer than 5% of Staphyloco

Infections caused by community-acquired (CA)-methicillin resistant Staphylococcus aureus (MRSA) have been reported worldwide. We assessed whether any common genetic markers existed among 117 CA-MRSA isolates from the United States, France, Switzerland, Australia, New Zealand, and Western Samoa by performing polymerase chain reaction for 24 virulence factors and the methicillin-resistance determinant. The genetic background of the strain was analyzed by pulsed-field gel electrophoresis (PFGE) and multi-locus sequence typing (MLST). The CA-MRSA strains shared a type IV SCCmec cassette and the Panton-Valentine leukocidin locus, whereas the distribution of the other toxin genes was quite specific to the strains from each continent. PFGE and MLST analysis indicated distinct genetic backgrounds associated with each geographic origin, although predominantly restricted to the agr3 background. Within each continent, the genetic background of CA-MRSA strains did not correspond to that of the hospital-acquired MRSA.

The expression of most Staphylococcus aureus virulence factors is controlled by the agr locus, which encodes a two-component signaling pathway whose activating ligand is an agr -encoded autoinducing peptide (AIP). A polymorphism in the amino acid sequence of the AIP and of its corresponding receptor divides S. aureus strains into four major groups. Within a given group, each strain produces a peptide that can activate the agr response in the other member strains, whereas the AIPs belonging to different groups are usually mutually inhibitory. We investigated a possible relationship between agr groups and human S. aureus disease by studying 198 S. aureus strains isolated from 14 asymptomatic carriers, 66 patients with suppurative infection, and 114 patients with acute toxemia. The agr group and the distribution of 24 toxin genes were analyzed by PCR, and the genetic background was determined by means of amplified fragment length polymorphism (AFLP) analysis. The isolates were relatively evenly distributed among the four agr groups, with 61 strains belonging to agr group I, 49 belonging to group II, 43 belonging to group III, and 45 belonging to group IV. Principal coordinate analysis performed on the AFLP distance matrix divided the 198 strains into three main phylogenetic groups, AF1 corresponding to strains of agr group IV, AF2 corresponding to strains of agr groups I and II, and AF3 corresponding to strains of agr group III. This indicated that the agr type was linked to the genetic background. A relationship between genetic background, agr group, and disease type was observed for several toxin-mediated diseases: for instance, agr group IV strains were associated with generalized exfoliative syndromes, and phylogenetic group AF1 strains with bullous impetigo. Among the suppurative infections, endocarditis strains mainly belonged to phylogenetic group AF2 and agr groups I and II. While these results do not show a direct role of the agr type in the type of human disease caused by S. aureus , the agr group may reflect an ancient evolutionary division of S. aureus in terms of this species’ fundamental biology.

Recent studies have shown that the annual incidence of infective endocarditis (IE) is stable between 15 and 60 cases per million.^1-4 However, since the first modern clinical description of IE by Osler,⁵ the profile of the disease has continuously evolved. This fact was highlighted in different epidemiological studies,^6,7 including a French survey of IE performed in 1991, in which the main results, compared with a similar study conducted in 1983,⁸ showed (1) stable annual incidence at 24 cases per million; (2) increased age of onset; (3) decreasing proportion of IE on abnormal native valve, compensated by an increased proportion of prosthetic valve IE and native valve IE in patients with previously unrecognized predisposing conditions; and (4) a changing microbiologic profile, with an increased proportion of group D streptococci and staphylococci.^1,9

Background. Observational studies showed that the profile of infective endocarditis (IE) significantly changed over the past decades. However, most studies involved referral centers. We conducted a population-based study to control for this referral bias. The objective was to update the description of characteristics of IE in France and to compare the profile of community-acquired versus healthcare-associated IE. Methods. A prospective population-based observational study conducted in all medical facilities from 7 French regions (32% of French individuals aged ≥18 years) identified 497 adults with Duke-Li–definite IE who were first admitted to the hospital in 2008. Main measures included age-standardized and sex-standardized incidence of IE and multivariate Cox regression analysis for risk factors of in-hospital death. Results. The age-standardized and sex-standardized annual incidence of IE was 33.8 (95% confidence interval [CI], 30.8–36.9) cases per million inhabitants. The incidence was highest in men aged 75–79 years. A majority of patients had no previously known heart disease. Staphylococci were the most common causal agents, accounting for 36.2% of cases (Staphylococcus aureus, 26.6%; coagulase-negative staphylococci, 9.7%). Healthcare-associated IE represented 26.7% of all cases and exhibited a clinical pattern significantly different from that of community-acquired IE. S. aureus as the causal agent of IE was the most important factor associated with in-hospital death in community-acquired IE (hazard ratio [HR], 2.82 [95% CI, 1.72–4.61]) and the single factor in healthcare-associated IE (HR, 2.54 [95% CI, 1.33–4.85]). Conclusions. S. aureus became both the leading cause and the most important prognostic factor of IE, and healthcare-associated IE appeared as a major subgroup of the disease.