Molecular Epidemiology of Staphylococcus epidermidis Implicated in Catheter-Related Bloodstream Infections at an Academic Hospital in Pretoria, South Africa

Abstract

<i>Staphylococcus epidermidis</i> is one of the most prevalent pathogens implicated in catheter-related bloodstream infections (CRBSI) at an academic hospital in Pretoria, South Africa. Little is known about the clonality and the prevalence of antibiotic resistance and virulence genes in <i>S. epidermidis</i> (e.g., <i>ica</i>AB, IS<i>256, mec</i>A, and <i>qac</i>A/B). A total of 508 intravascular catheters (IVCs) from 331 patients were submitted for culture from May to October 2013. Only 50% (<i>n</i> = 253/508) of the IVCs were accompanied by blood cultures (BCs) taken within 48 h. Forty-four percent (44%; <i>n</i> = 112/253) of IVCs were colonised, of which 26% (<i>n</i> = 65/253) were associated with a CRBSI. We identified <i>S. epidermidis</i> as the causal agent in 31% (<i>n</i> = 20/65) of the CRBSI cases. Fifty-nine <i>S. epidermidis</i> isolates were obtained, 23 isolates were cultured from 22 IVCs and 36 isolates were cultured from 36 BCs. All <i>S. epidermidis</i> isolates were resistant to β-lactams (100%; <i>n</i> = 59/59), followed by high levels of resistance toward erythromycin (86%; <i>n</i> = 51/59) and gentamicin (81%; <i>n</i> = 49/59). The <i>mec</i>A gene was prevalent in all the (100%, <i>n</i> = 59/59) isolates. Isolates contained the IS<i>256</i> element (83%, <i>n</i> = 49/59), the <i>ica</i>AB gene (81%, <i>n</i> = 48/59) and, the <i>qac</i>A/B gene (81%, <i>n</i> = 48/59). All 48 isolates were <i>qac</i>A positive upon restriction enzyme digestion of the <i>qac</i>A/B amplicons. Phenotypic resistance toward 0.5% (m/v) chlorhexidine was not observed. Staphylococcal Cassette Chromosome (SCC) <i>mec</i> typing showed that SCC<i>mec</i> type IV (31%; <i>n</i> = 18/59) was the most prevalent. The remaining SCC<i>mec</i> elements were highly diverse. Pulsed-field gel electrophoresis (PFGE) showed that <i>S. epidermidis</i> isolates from individual patients were mostly clonal. Multilocus sequencing typing (MLST) of 10 sequenced isolates showed that sequence type (ST) 2 (40%; <i>n</i> = 4/10) was the most frequently detected, followed by ST54 (20%; <i>n</i> = 2/10), ST28 (10%; <i>n</i> = 1/10), ST59 (10%; <i>n</i> = 1/10) and ST490 (10%; 1/10). One isolate was newly assigned to ST596. These <i>S. epidermidis</i> infections can be attributed to patients' skin microflora or to poor infection control practices. Currently, <i>S. epidermidis</i> strains circulating in the studied hospital are multidrug-resistant and highly adaptive to environmental changes.