| Summary: | The ability of <i>Staphylococcus epidermidis</i> to produce virulence factors, such as biofilm, added to its increased resistance to antimicrobials can cause infections that are difficult to treat. Many staphylococcal virulence factors are under the control of the accessory gene regulator (<i>agr</i>). The objective of this study was to establish the <i>agr</i> locus and susceptibility of biofilm-producing <i>S. epidermidis</i> specimens to antimicrobial agents, through PCR reactions, reverse transcription polymerase chain reaction (RT-PCR), and the determination of minimum inhibitory concentration (MIC), and to analyze the clonal profile of 300 strains isolated from blood culture specimens from inpatients at a University Hospital in Brazil, over a 20-year period by pulsed-field gel electrophoresis (PFGE) and multilocus sequence typing (MLST) techniques. The <i>ica</i> operon expression was shown in 83.6% strains, <i>bhp</i> gene in 11.5%, and <i>aap</i> gene in 32.8%. Oxacillin resistance was detected in 90.1%, while 4.9% showed tigecycline resistance, and intermediate resistance to quinupristin/dalfopristin was identified in 0.4%. Clonal profile determination showed 11 clusters, with the ST2 type determined as the major cluster. The <i>S. epidermidis</i> biofilm producer demonstrated a predominance of <i>agr</i> I locus, oxacillin resistance, and SCC<i>mec</i> III as well as the potential dissemination of pathogenic clones in hospital settings over long periods.
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