Phenotypic and genotypic characterization of Staphylococci causing breast peri-implant infections in oncologic patients

Background: Staphylococcus epidermidis and S. aureus have been identified as the most common bacteria responsible for sub-clinical and overt breast implant infections and their ability to form biofilm on the implant as been reported as the essential factor in the development of this type of infections. Biofilm formation is a complex process with the participation of several distinct molecules, whose relative importance in different clinical settings has not yet been fully elucidated. To our knowledge this is the first study aimed at characterizing isolates causing breast peri-implant infections. Results: Thirteen S. aureus and seven S. epidermidis causing breast peri-implant infections were studied. Using the broth microdilution method and the E-test, the majority of the strains were susceptible to all antibiotics tested. Methicillin resistance was detected in two S. epidermidis. All strains had different RAPD profiles and were able to produce biofilms in microtitre plate assays but, while all S. aureus carried and were able to express icaA and icaD genes, this was only true for one S. epidermidis. Biofilm development was glucose-and NaCl-induced (5 S. aureus and 1 S. epidermidis) or glucose-induced (the remaining strains). Proteinase K and sodium metaperiodate treatment had different effects on biofilms dispersion revealing that the strains studied were able to produce chemically different types of extracellular matrix mediating biofilm formation. All S. aureus strains harboured and expressed the atlA, clfA, FnA, eno and cna genes and the majority also carried and expressed the sasG (10/13), ebpS (10/13) genes. All S. epidermidis strains harboured and expressed the atlE, aae, embp genes, and the majority (six strains) also carried and expressed the fbe, aap genes. Genes for S. aureus capsular types 5 and 8 were almost equally distributed. The only leukotoxin genes detected were lukE/lukD (6/13). Conclusions: S. aureus and S. epidermidis breast peri-implant infections are caused by heterogeneous strains with different biofilm development mechanisms. Since the collagen adhesin (cna) gene is not ubiquitously distributed among S. aureus, this protein could have an important role in the cause of breast peri-implant infections.