Abstract:
Staphylococcus epidermidis 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 S. epidermidis (e.g., icaAB, IS256, mecA, and qacA/B). A total
of 508 intravascular catheters (IVCs) from 331 patients were submitted for culture from
May to October 2013. Only 50% (n = 253/508) of the IVCs were accompanied by blood
cultures (BCs) taken within 48 h. Forty-four percent (44%; n = 112/253) of IVCs were
colonised, of which 26% (n = 65/253) were associated with a CRBSI. We identified
S. epidermidis as the causal agent in 31% (n = 20/65) of the CRBSI cases. Fifty-nine
S. epidermidis isolates were obtained, 23 isolates were cultured from 22 IVCs and 36
isolates were cultured from36 BCs. All S. epidermidis isolates were resistant to b-lactams
(100%; n = 59/59), followed by high levels of resistance toward erythromycin (86%;
n = 51/59) and gentamicin (81%; n = 49/59). The mecA gene was prevalent in all the
(100%, n = 59/59) isolates. Isolates contained the IS256 element (83%, n = 49/59), the
icaAB gene (81%, n=48/59) and, the qacA/B gene (81%, n=48/59). All 48 isolateswere
qacA positive upon restriction enzyme digestion of the qacA/B amplicons. Phenotypic
resistance toward 0.5% (m/v) chlorhexidine was not observed. Staphylococcal Cassette
Chromosome (SCC) mec typing showed that SCCmec type IV (31%; n = 18/59) was the
most prevalent. The remaining SCCmec elements were highly diverse. Pulsed-field gel
electrophoresis (PFGE) showed that S. epidermidis isolates from individual patients were
mostly clonal. Multilocus sequencing typing (MLST) of 10 sequenced isolates showed
that sequence type (ST) 2 (40%; n = 4/10) was the most frequently detected, followed by ST54 (20%; n = 2/10), ST28 (10%; n = 1/10), ST59 (10%; n = 1/10) and ST490 (10%; 1/10). One isolate was newly assigned to ST596. These S. epidermidis infections
can be attributed to patients’ skin microflora or to poor infection control practices.
Currently, S. epidermidis strains circulating in the studied hospital are multidrug-resistant
and highly adaptive to environmental changes.
