Biofilm formation is a common feature of staphylococci conferring protection against unfavorable environmental conditions, and contributing (in pathogenic species) to treatment recalcitrance and chronic infections. Biofilms are surface-attached bacterial communities surrounded by a self-produced extracellular matrix consisting of polysaccharides and/or proteins. In staphylococci, the main polysaccharide biofilm matrix component is PIA (polysaccharide intercellular adhesin). PIA is produced by the gene products of the icaADBC operon which are controlled by the adjacent repressor IcaR. Recently, we characterized a multiresistance plasmid isolated from livestock-associated methicillin-resistant Staphylococcus aureus strain Rd11 [1]. Unexpectedly, this plasmid (pAFS11) harboured, in addition to resistance genes, a novel ica-like gene cluster. Bioinformatic analysis demonstrated that the pAFS11 ica genes originated from the animal-associated species Staphylococcus sciuri and had been acquired by S. aureus Rd11 via horizontal gene transfer. Here, we tested livestock-associated S. sciuri isolates for ica gene presence and function. We found 75 % of 158 S. sciuri isolates tested to carry the ica gene cluster. However, none of the isolates formed a PIA-mediated biofilm. Also in S. aureus Rd11, carrying the S. sciuri ica genes on plasmid pAFS11, no PIA biofilm formation occurred. Interestingly, like all S. aureus strains, Rd11 harbours its own chromosomally encoded ica gene cluster, and transformation of pAFS11 into a PIA-producing S. aureus strain resulted in reduced PIA production. Preliminary experiments suggest a regulatory crosstalk between plasmid-encoded S. sciuri IcaR with the chromosomal S. aureus icaADBC operon. The data highlight ongoing genetic exchange across staphylococcal species borders which, in addition to resistance genes, may also comprise transfer of virulence traits. We hypothesize that co-selection of virulence factors by antibiotics and their integration into the regulatory circuits of the host bacterium might play an important, but still poorly understood role in the emergence of bacteria with novel resistance and virulence traits.