Anne Tristan

egc, A Highly Prevalent Operon of Enterotoxin Gene, Forms a Putative Nursery of Superantigens in Staphylococcus aureus

The recently described staphylococcal enterotoxins (SE) G and I were originally identified in two separate strains of Staphylococcus aureus. We have previously shown that the corresponding genes seg and sei are present in S. aureus in tandem orientation, on a 3.2-kb DNA fragment (Jarraud, J. et al. 1999. J. Clin. Microbiol. 37:2446–2449). Sequence analysis of seg-sei intergenic DNA and flanking regions revealed three enterotoxin-like open reading frames related to seg and sei, designated sek, sel, and sem, and two pseudogenes, ψ ent1 and ψ ent2. RT-PCR analysis showed that all these genes, including seg and sei, belong to an operon, designated the enterotoxin gene cluster (egc). Recombinant SEG, SEI, SEK, SEL, and SEM showed superantigen activity, each with a specific Vβ pattern. Distribution studies of genes encoding superantigens in clinical S. aureus isolates showed that most strains harbored such genes and in particular the enterotoxin gene cluster, whatever the disease they caused. Phylogenetic analysis of enterotoxin genes indicated that they all potentially derived from this cluster, identifying egc as a putative nursery of enterotoxin genes.

Global Distribution of Panton-Valentine Leukocidin–positive Methicillin-resistant Staphylococcus aureus, 2006

Some formerly continent-specific clones have now spread around the world

Bacterial Competition for Human Nasal Cavity Colonization: Role of Staphylococcal agr Alleles

ABSTRACT We examined the bacterial aerobic nasal flora of 216 healthy volunteers to identify potential competitive interactions among different species, with special emphasis on the influence of staphylococcal agr alleles. The Staphylococcus aureus colonization rate correlated negatively with the rate of colonization by Corynebacterium spp. and non-aureus staphylococci, especially S. epidermidis, suggesting that both Corynebacterium spp. and S. epidermidis antagonize S. aureus colonization. Most of the S. aureus and S. epidermidis isolates were agr typed by a PCR method. Only one S. aureus agr (agrSa) allele was detected in each carrier. Multiple logistic regression of the two most prevalent agrSa alleles (agr-1Sa and agr-2Sa) and the three S. epidermidis agr (agrSe) alleles showed a specific influence of the agr system. The results of this model did not support conclusions drawn from previous in vitro agr-specific cross-inhibition experiments. Our findings suggest that the agr alleles, which are strongly linked to the bacterial genetic background, may simply be associated with common biological properties—including mediators of bacterial interference—in the strains that bear them.

Use of Multiplex PCR To Identify Staphylococcus aureus Adhesins Involved in Human Hematogenous Infections

ABSTRACT We have developed a multiplex PCR procedure to determine the distribution of nine adhesin genes in Staphylococcus aureus isolates. Only genes encoding bone sialoprotein binding protein and fibronectin binding protein B were significantly associated with hematogenous osteomyelitis/arthritis and native-valve endocarditis, respectively, suggesting their involvement in hematogenous tissue infections.

Global Distribution and Evolution of Panton- Valentine Leukocidin-Positive Methicillin-Susceptible Staphylococcus aureus, 1981-2007

BACKGROUND Panton-Valentine leukocidin (PVL)-positive methicillin-susceptible Staphylococcus aureus and methicillin-resistant S. aureus (MSSA and MRSA, respectively) are both associated with severe infections, such as necrotizing pneumonia. The epidemiological profile of PVL-positive community-acquired (CA) MRSA has been extensively studied, but few corresponding data on PVL-positive MSSA are available. OBJECTIVES The objectives of the study were to investigate the global population structure of PVL-positive MSSA, to compare it with that reported for CA-MRSA, and thus to examine the phylogenetic relationship between these pathogens. METHODS We determined the agr types, multilocus sequence types, and toxin gene profiles of 211 PVL-positive MSSA clinical isolates collected in 19 countries throughout the world between 1981 and 2007. RESULTS The predominant lineages of PVL-positive MSSA were agr3/ST30, agr4/ST121, agr3/ST1, agr2/ST5, and agr3/ST80. Except for agr4/ST121, these lineages are also reported to be prevalent among CA-MRSA. PVL-positive MSSA lineages that are genetically related to CA-MRSA have gradually replaced other lineages (especially agr4/ST121) over the past 2 decades. Within a given sequence type, the toxin gene content of PVL-positive MSSA strains was very similar to that of PVL-positive CA-MRSA. CONCLUSIONS The molecular epidemiological profiles of PVL-positive MSSA and CA-MRSA are dynamically interrelated, with the former appearing to constitute a reservoir for the latter.

Virulence determinants in community and hospital meticillin-resistant Staphylococcus aureus

Staphylococcus aureus produces many virulence factors, most of which act in a synergistic and coordinated fashion. Some appear to be specifically associated with certain severe infections and are produced by meticillin-resistant Staphylococcus aureus (MRSA) clones distributed worldwide. Superantigenic exotoxins appear to be major virulence factors in hospital MRSA clones (HA-MRSA), and staphylococcal enterotoxin A (SEA) may be involved in the physiopathology of septic shock. Panton Valentine Leucocidin (PVL) has emerged as a major virulence factor in community-acquired Staphylococcus aureus (CA-MRSA) infections. In particular, the leukotoxic action of PVL is responsible for the high mortality rate associated with necrotizing pneumonia. CA-MRSA can also harbour the toxic shock toxin 1 (TSST-1) and rarely the exfoliative toxin.

Staphylococcus aureus Isolates Associated with Necrotizing Pneumonia Bind to Basement Membrane Type I and IV Collagens and Laminin

To investigate how Panton-Valentine leukocidin (PVL)-positive Staphylococcus aureus (PPSA) strains associate with specific bronchial lesions during community-acquired necrotizing pneumonia, we examined PPSA strains and PVL-negative S. aureus (PNSA) strains for their binding behavior to extracellular matrix (ECM) proteins, primary human airway epithelial cell (HAEC) cultures, and human airway mucosa damaged ex vivo. Compared with PNSA strains, PPSA strains exhibited increased affinity for damaged airway epithelium and especially for exposed basement membrane. PPSA strains, compared with PNSA strains, showed stronger affinity for type I and IV collagens and laminin, a property associated with the presence of the cna gene. PPSA and PNSA culture supernatants similarly damaged HAEC layers, whereas recombinant PVL had no effect, suggesting that an S. aureus exoprotein other than PVL might contribute to the observed airway epithelial damage. These results suggest that epithelial damage, possibly due to viral infection (which usually precedes necrotizing pneumonia) and/or to a non-PVL S. aureus exoproduct action, may permit binding of PPSA to exposed type I and IV collagens and laminin--the PVL cytotoxin being involved later during necrotizing pneumonia.

MRSA Harboring mecA Variant Gene mecC, France

We describe human cases and clustered animal cases of mecALGA251–positive methicillin-resistant Staphylococcus aureus in France. Our report confirms that this new variant has a large distribution in Europe. It may represent a public health threat because phenotypic and genotypic tests seem unable to detect this new resistance mechanism.

Frequent carriage of Panton-Valentine leucocidin genes by Staphylococcus aureus isolates from surgically drained abscesses.

ABSTRACT Between 1 February and 15 April 2002, 95 patients were admitted to Gaston Bourret Territorial Hospital (New Caledonia, France) for drainage of community-acquired soft tissue abscesses. Staphylococcus aureus was detected in 68 cases (72%). Two-thirds of the patients with S. aureus infection had furuncles, which were located on the limbs in 82% of cases. The median interval between symptom onset and hospital admission was 5.7 days. Three-quarters of the patients were Melanesians living in tribes. Fifty-four S. aureus isolates were screened for toxin genes. Panton-Valentine leucocidin (PVL) genes were detected in 48 isolates (89%), the exfoliative toxin A gene was detected in 1 isolate, and no toxin genes were detected in 4 isolates. S. aureus nasal carriage was detected in 39.7% of patients with S. aureus infections. Two infecting S. aureus strains and two nasal carriage strains were resistant to methicillin. Comparative pulsed-field gel electrophoresis, performed in 16 cases, showed that five of six patients with PVL-positive nasal carriage strains were infected by the same strains. In contrast, 8 of 10 patients with PVL-negative nasal carriage strains were infected by PVL-positive strains. PVL genes thus appear to be a major virulence factor in both primary and secondary S. aureus skin infections.

Pneumonia and new methicillin-resistant Staphylococcus aureus clone.

Necrotizing pneumonia caused by Staphylococcus aureus strains carrying the Panton-Valentin leukocidin gene is a newly described disease entity. We report a new fatal case of necrotizing pneumonia. An S. aureus strain with an agr1 allele and of a new sequence type 377 was recovered, representing a new, emerging, community-acquired methicillin-resistant clone.