Fifty-four Staphylococcus epidermidis strains responsible for infections of joint prostheses and 23 strains isolated from skin flora were studied for markers of virulence, to discriminate invasive strains from normal flora. They were screened for binding to polystyrene and matrix proteins and for the presence of staphylococcal genes involved in adhesion. The ica operon involved in biofilm formation was the only marker discriminating between these 2 categories of strains.

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The atlC gene (1,485 bp), encoding an autolysin which binds fibronectin, and the ica operon, involved in biofilm formation, were isolated from the chromosome of an infectious isolate of Staphylococcus caprae and sequenced. AtlC (155 kDa) is similar to the staphylococcal autolysins Atl, AtlE, Aas (48 to 72% amino acid identity) and contains a putative signal peptide of 29 amino acids and two enzymatic centers (N-acetylmuramoyl-L-alanine amidase and endo-␤-N-acetylglucosaminidase) interconnected by three imperfect fibronectin-binding repeats. The glycine-tryptophan (GW) motif found in the central and end part of each repeat may serve for cell surface anchoring of AtlC as they do in Listeria monocytogenes. The S. caprae ica operon contains four genes closely related to S. epidermidis and S. aureus icaA, icaB, icaC, and icaD genes (> 68% similarity) and is preceded by a gene similar to icaR (>70% similarity). The polypeptides deduced from the S. caprae ica genes exhibit 67 to 88% amino acid identity to those of S. epidermidis and S. aureus ica genes. The ica operon and icaR gene were analyzed in 14 S. caprae strains from human specimens or goats' milk. Some of the strains produced biofilm, and others did not. All strains carry the ica operon and icaR of the same sizes and in the same relative positions, suggesting that the absence of biofilm formation is not related to the insertion of a mobile element such as an insertion sequence or a transposon.Staphylococcus caprae (13) is the predominent species among the staphylococci recovered from mastitis-free goats' milk (5). It is also increasingly recognized as a human pathogen infecting implanted foreign bodies (1,6,14,44,46,52). Despite the amended description of this species (25), its phenotypic identification remains difficult. Therefore, molecular identification methods such as the analysis of ribotypes (1, 5, 12, 52), DNA-DNA hybridization (25), sequencing of the 16S rRNA gene (46), or analysis of the banding patterns on gels of penicillin-binding proteins (24) have been used for ecological studies and investigation of the involvement of S. caprae in infections. Some S. caprae strains from human specimens and goats' milk form biofilms (1, 4). Other strains do not, although the genomes of all strains tested carry nucleotide sequences hybridizing, at low stringency, with the S. epidermidis genes involved in initial adherence (atlE) and biofilm accumulation (the ica operon) (1). S. caprae adherence to fibronectin-and gelatin-coated coverslips is very weak. Nevertheless, surface proteins binding fibronectin have been detected on all S. caprae strains tested (1). The N-terminal part of the 175-kDa fibronectin-binding protein released from the surface of S. caprae clinical isolate 96007 has more than 50% amino acid identity (1) to the N-terminal part of the staphylococcal autolysins Atl (38), AtlE (18), and Aas (20). The aim of this study was to isolate the atlC autolysin gene of isolate 96007 to check whether the purified protein encoded by this gene binds fibronectin. ...

A gene encoding an acetyltransferase inactivating streptogramin A (SgA) and structurally similar compounds was isolated from a staphylococcal plasmid and sequenced. This gene, designated vatB, potentially encodes a 212-amino-acid protein, VatB, of 23,320 Da with 47.4 and 58.4% amino acid identities with two other enzymes with the same activity, Vat and SatA, respectively, which are encoded by a staphylococcal plasmid and an enterococcal plasmid, respectively. The C-terminal parts of these three enzymes share significant homology with the C-terminal parts of 10 other acetyltransferases modifying various substrates. A pair of degenerate primers representing the conserved motifs shared by VatB, Vat, and SatA was designed to detect the three genes encoding these SgA acetyltransferases. Five of 12 clinical SgA r Staphylococcus aureus isolates tested carried neither these genes nor the gene vga, which confers resistance to SgA by a different mechanism, suggesting that another gene(s) and possibly another mechanism of resistance to SgA in staphylococci remains to be characterized.

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