François Vandenesch

Involvement of Panton-Valentine Leukocidin—Producing Staphylococcus aureus in Primary Skin Infections and Pneumonia

Panton-Valentine leukocidin (PVL) is a cytotoxin that causes leukocyte destruction and tissue necrosis. It is produced by fewer than 5% of Staphylococcus aureus strains. A collection of 172 S. aureus strains were screened for PVL genes by polymerase chain reaction amplification. PVL genes were detected in 93% of strains associated with furunculosis and in 85% of those associated with severe necrotic hemorrhagic pneumonia (all community-acquired). They were detected in 55% of cellulitis strains, 50% of cutaneous abscess strains, 23% of osteomyelitis strains, and 13% of finger-pulp-infection strains. PVL genes were not detected in strains responsible for other infections, such as infective endocarditis, mediastinitis, hospital-acquired pneumonia, urinary tract infection, and enterocolitis, or in those associated with toxic-shock syndrome. It thus appears that PVL is mainly associated with necrotic lesions involving the skin or mucosa.

Community-Acquired Methicillin-Resistant Staphylococcus aureus Carrying Panton-Valentine Leukocidin Genes: Worldwide Emergence

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.

Association between Staphylococcus aureus strains carrying gene for Panton-Valentine leukocidin and highly lethal necrotising pneumonia in young immunocompetent patients

BACKGROUND Between 1986 and 1998, eight cases of community-acquired pneumonia due to Staphylococcus aureus strains carrying the gene for the Panton-Valentine leukocidin (PVL) were recorded in France, six of which were fatal. We aimed to assess the clinical features of these eight cases, and those of other cases identified prospectively, and to compare them with the characteristics of patients with pneumonia caused by PVL-negative strains. METHODS We compared eight retrospective and eight prospective cases of PVL-positive S aureus pneumonia with 36 cases of PVL-negative S aureus pneumonia. For all patients, we recorded age, length of hospital stay, risk factors for infection, signs and symptoms, laboratory findings, antibiotic treatment, and serial radiological findings. FINDINGS Median age was 14.8 years (IQR 5.4-24.0) for the PVL-positive patients and 70.1 years (59.2-81.4) for the others (p=0.001). Influenza-like illness had occurred during the 2 days before admission in 12 of the 16 PVL-positive patients, but in only three of 33 PVL-negative patients (p<0.001). PVL-positive infections were more often marked by: temperature greater than 39 degrees C (p=0.01), heart rate above 140 beats per min (p=0.02), haemoptysis (p=0.005), onset of pleural effusion during hospital stay (p=0.004), and leucopenia (p=0.001). The survival rate 48 h after admission was 63% for the PVL-positive patients and 94% for PVL-negative individuals (p=0.007). Histopathological examination of lungs at necropsy from three cases of necrotising pneumonia associated with PVL-positive S aureus showed extensive necrotic ulcerations of the tracheal and bronchial mucosa and massive haemorrhagic necrosis of interalveolar septa. INTERPRETATION PVL-producing S aureus strains cause rapidly progressive, haemorrhagic, necrotising pneumonia, mainly in otherwise healthy children and young adults. The pneumonia is often preceded by influenza-like symptoms and has a high lethality rate.

Relationships between Staphylococcus aureus Genetic Background, Virulence Factors, agr Groups (Alleles), and Human Disease

ABSTRACT 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 agrgroups, 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.

Staphylococcus aureus Panton-Valentine Leukocidin Causes Necrotizing Pneumonia

The Staphylococcus aureus Panton-Valentine leukocidin (PVL) is a pore-forming toxin secreted by strains epidemiologically associated with the current outbreak of community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) and with the often-lethal necrotizing pneumonia. To investigate the role of PVL in pulmonary disease, we tested the pathogenicity of clinical isolates, isogenic PVL-negative and PVL-positive S. aureus strains, as well as purified PVL, in a mouse acute pneumonia model. Here we show that PVL is sufficient to cause pneumonia and that the expression of this leukotoxin induces global changes in transcriptional levels of genes encoding secreted and cell wall–anchored staphylococcal proteins, including the lung inflammatory factor staphylococcal protein A (Spa).

COMMUNITY-ACQUIRED METHICILLIN-RESISTANT STAPHYLOCOCCUS AUREUS INFECTIONS IN FRANCE: EMERGENCE OF A SINGLE CLONE THAT PRODUCES PANTON-VALENTINE LEUKOCIDIN

To characterize the clinical and bacteriologic characteristics of community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA) infections, we reviewed 14 cases that were diagnosed in previously healthy patients during an 18-month period in France. Eleven patients had skin or soft-tissue infections. Two patients died of CA-MRSA necrotizing pneumonia. A case of pleurisy occurred in a child who acquired CA-MRSA from his mother, who had a breast abscess. The Panton-Valentine leukocidin genes and the lukE-lukD leukocidin genes were detected in all 14 isolates. The clonal origin of all of the isolates was demonstrated on the basis of their pulsotypes and antibiotic resistance profiles. All isolates had an agr3 allele. The combination of the Panton-Valentine leukocidin determinant (which encodes a virulence factor for primary skin infection and pneumonia) with the mecA gene (which confers antibiotic resistance and epidemicity) appears to have created a superadapted S. aureus strain that is spreading in the community.

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.

Cultivation of the bacillus of Whipple's disease

BACKGROUND Whipples disease is a systemic bacterial infection, but to date no isolate of the bacterium has been established in subculture, and no strain of this bacterium has been available for study. METHODS Using specimens from the aortic [corrected] valve of a patient with endocarditis due to Whipples disease, we isolated and propagated a bacterium by inoculation in a human fibroblast cell line (HEL) with the use of a shell-vial assay. We tested serum samples from our patient, other patients with Whipples disease, and control subjects for the presence of antibodies to this bacterium. RESULTS The bacterium of Whipples disease was grown successfully in HEL cells, and we established subcultures of the isolate. Indirect immunofluorescence assays showed that the patients serum reacted specifically against the bacterium. Seven of 9 serum samples from patients with Whipples disease had IgM antibody titers of 1:50 or more, as compared with 3 of 40 samples from the control subjects (P<0.001). Polyclonal antibodies against the bacterium were generated by inoculation of the microorganism into mice and were used to detect bacteria in the excised cardiac tissue from our patient on immunohistochemical analysis. The 16S ribosomal RNA gene of the cultured bacterium was identical to the sequence for Tropheryma whippelii identified previously in tissue samples from patients with Whipples disease. The strain we have grown is available in the French National Collection. CONCLUSIONS We cultivated the bacterium of Whipples disease, detected specific antibodies in tissue from the source patient, and generated specific antibodies in mice to be used in the immunodetection of the microorganism in tissues. The development of a serologic test for Whipples disease may now be possible.

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

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

Theagr P2 operon: An autocatalytic sensory transduction system inStaphylococcus aureus

The synthesis of virulence factors and other exoproteins inStaphylococcus aureus is controlled by the global regulator,agr. Expression of secreted proteins is up-regulated in the postexponential growth phase, whereas expression of surface proteins is down-regulated byagr. Theagr locus consists of two divergent operons, transcribed from neighboring but non-overlapping promoters, P2 and P3. The P2 operon sequence, reported here, contains 4 open reading frames,agr A, C, D, andB, of whichA andC appear to encode proteins of a classical 2-component signal transduction pathway. The P3 operon specifies a 0.5 kb transcript, RNA III, which is the actual effector of theagr response, and, incidentally, encodes theagr-regulated peptide δ-hemolysin. Transcriptional fusions have shown that both P2 and P3 areagr sensitive (function in anagr+ but not in anagr background) and deletion analysis has shown that all four of the P2 ORFs are involved;agrA andagrC seem to be absolutely required for the transcriptional activation of theagr locus, whereasagrB andagrD seem to be partially required. Since transcription of P2 requires P2 operon products, the P2 operon is autocatalytic, and is thus admirably suited to the need for rapid production of exo-proteins at a time when overall growth is coming to a halt.