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.

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.

No 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 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 toxinmediated 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.

Methicillin-resistant Staphylococcus aureus (MRSA) strains have become prevalent in health care facilities and in the community worldwide (3, 4). MRSA strains produce penicillin binding protein 2Ј or 2a, which is poorly acylated by ␤-lactam antibiotics (5,22,25). The mecA gene, encoding PBP2a, is carried on a peculiar type of mobile genetic element inserted into the staphylococcal chromosome, designated staphylococcal cassette chromosome mec (SCCmec) elements (12,14,24).SCCmec elements typically share four characteristics: first, they carry the mec gene complex (mec) consisting of the methicillin resistance determinant mecA and its regulatory genes and insertion sequences; second, they carry the ccr gene complex (ccr) consisting of ccr genes that are responsible for the mobility of the element and its surrounding sequences; third, they have characteristic directly repeated nucleotide sequences and inverted complementary sequences at both ends; and last, they integrate into the 3Ј end of an open reading frame (ORF), orfX.Despite these similarities, the structures of SCCmec elements are rather divergent. Allotypic differences that are used for SCCmec type definitions have been identified in both ccr and mec. Five types of ccr and four classes of mec have been reported. ccr types 1 to 4 carry the ccrA and ccrB genes, which share approximately 80% identity with each other, and the type 5 ccr carries the ccrC gene (10,11,17,19). Four classes of the mec gene complexes have been identified among methicillinresistant staphylococcal strains of various species: class A mec, consisting of IS431mec-mecA-mecR1-mecI; class B mec, consisting of IS431mec-mecA-⌬mecR1-IS1272; class C mec, consisting of IS431mec-mecA-⌬mecR1-IS431; and class D mec, consisting of IS431mec-mecA-⌬mecR1 with no insertion sequences downstream of ⌬mecR1 identified by PCR as of yet (13). In S. aureus strains, mec classes A, B, and C have been identified. Insertion sequences have sometimes been found to be integrated in or around the class A mec. A class A mec carrying IS431 downstream of mecI was found in Staphylococcus haemolyticus (13). Recently, Shore et al. identified MRSA strains carrying class A mec with an insertion of IS1182 in and around the mecI gene and designated them classes A3 and A4 (23).The SCCmec element type has been defined by the combination of ccr type and mec class. In MRSA strains, six types of SCCmec elements, that is, six combinations of ccr and mec, have been reported (Table 1). These six SCCmec elements have been further classified by differences in regions other than ccr and mec, which are designated junkyard (J) regions. The J regions comprise three parts: J1 (the region between ccr and the right-flanking chromosomal region), J2 (the region between mec and ccr), and J3 (the region between orfX and mec). The J regions are not always specific to each SCCmec type, but certain J regions are commonly shared among certain types of SCCmec elements. Of the three regions, we regard J1 as being the most fundamental, because we presume t...