Biofilm production is an important step in the pathogenesis of Staphylococcus epidermidis polymer-associated infections and depends on the expression of the ica ADBC operon leading to the synthesis of a polysaccharide intercellular adhesin. A chromosomally encoded reporter gene fusion between the ica promoter and the beta-galactosidase gene lac Z from Escherichia coli was constructed and used to investigate the influence of both environmental factors and subinhibitory concentrations of different antibiotics on ica expression in S. epidermidis . It was shown that S. epidermidis biofilm formation is induced by external stress (i.e., high temperature and osmolarity). Subinhibitory concentrations of tetracycline and the semisynthetic streptogramin antibiotic quinupristin-dalfopristin were found to enhance ica expression 9- to 11-fold, whereas penicillin, oxacillin, chloramphenicol, clindamycin, gentamicin, ofloxacin, vancomycin, and teicoplanin had no effect on ica expression. A weak (i.e., 2.5-fold) induction of ica expression was observed for subinhibitory concentrations of erythromycin. The results were confirmed by Northern blot analyses of ica transcription and quantitative analyses of biofilm formation in a colorimetric assay.

Osmotic stress was found to induce biofilm formation in a Staphylococcus aureus mucosal isolate. Inactivation of a global regulator of the bacterial stress response, the alternative transcription factor ς ^B , resulted in a biofilm-negative phenotype and loss of salt-induced biofilm production. Complementation of the mutant strain with an expression plasmid encoding ς ^B completely restored the wild-type phenotype. The combined data suggest a critical role of ς ^B in S. aureus biofilm regulation under environmental stress conditions.

Staphylococcus epidermidis is a normal constituent of the healthy human microflora, but it is also the most common cause of nosocomial infections associated with the use of indwelling medical devices. Isolates from device-associated infections are known for their pronounced phenotypic and genetic variability, and in this study we searched for factors that might contribute to this flexibility. We show that mutator phenotypes, which exhibit elevated spontaneous mutation rates, are rare among both pathogenic and commensal S. epidermidis strains. However, the study revealed that, in contrast to those of commensal strains, the genomes of clinical S. epidermidis strains carry multiple copies of the insertion sequence IS 256 , while other typical staphylococcal insertion sequences, such as IS 257 and IS 1272 , are distributed equally among saprophytic and clinical isolates. Moreover, detection of IS 256 was found to be associated with biofilm formation and the presence of the icaADBC operon as well as with gentamicin and oxacillin resistance in the clinical strains. The data suggest that IS 256 is a characteristic element in the genome of multiresistant nosocomial S. epidermidis isolates that might be involved in the flexibility and adaptation of the genome in clinical isolates.

Staphylococcus epidermidis is part of the normal microflora of the human skin but is also a leading cause of device-associated infections in critically ill patients. Commensal and clinical S. epidermidis isolates differ in their ability to form biofilms on medical devices; the synthesis of biofilms is mediated by the icaADBC operon. Currently, the epidemiological relatedness between ica- positive and -negative isolates is not known; neither is it known whether the ica genes can spread to biofilm-negative strains through horizontal gene transfer. In this study, multilocus sequence typing (MLST) was employed for the clonal analysis of 118 S. epidermidis ica -positive and -negative strains. MLST revealed that the majority of ica -positive and -negative strains were closely related and formed a single clonal complex. Within this complex one sequence type (ST27) was identified which contained exclusively ica- positive isolates and represented the majority of clinical strains tested. ST27 and related ica -positive clones carried different SCC mec cassettes (conferring methicillin resistance) and the insertion sequence IS 256 . The findings suggest that the S. epidermidis infections analyzed in this report are mainly caused by a single clone (ST27) which occurs preferentially in hospitals and differs from clones in the community. It is hypothesized that the successful establishment of ST27 within nosocomial environments has been facilitated by the presence of genes encoding biofilm and resistance traits.

Coagulase-negative staphylococci (CoNS) are common opportunistic pathogens, but also ubiquitous human and animal commensals. Infection-associated CoNS from healthcare environments are typically characterized by pronounced antimicrobial resistance (AMR) including both methicillin- and multidrug-resistant isolates. Less is known about AMR patterns of CoNS colonizing the general population. Here we report on AMR in commensal CoNS recovered from 117 non-hospitalized volunteers in a region of Germany with a high livestock density. Among the 69 individuals colonized with CoNS, 29 had reported contacts to either companion or farm animals. CoNS were selectively cultivated from nasal swabs, followed by species definition by 16S rDNA sequencing and routine antibiotic susceptibility testing. Isolates displaying phenotypic AMR were further tested by PCR for presence of selected AMR genes. A total of 127 CoNS were isolated and Staphylococcus epidermidis (75%) was the most common CoNS species identified. Nine isolates (7%) were methicillin-resistant (MR) and carried the mecA gene, with seven individuals (10%) being colonized with at least one MR-CoNS isolate. While resistance against gentamicin, phenicols and spectinomycin was rare, high resistance rates were found against tetracycline (39%), erythromycin (33%) and fusidic acid (24%). In the majority of isolates, phenotypic resistance could be associated with corresponding AMR gene detection. Multidrug-resistance (MDR) was observed in 23% (29/127) of the isolates, with 33% (23/69) of the individuals being colonized with MDR-CoNS. The combined data suggest that MR- and MDR-CoNS are present in the community, with previous animal contact not significantly influencing the risk of becoming colonized with such isolates.