Geoffrey Coombs

Aim: To profile the genomic diversity of 27 Staphylococcus epidermidis isolates collected from 21 patients with peritonitis episodes presenting to Sir Charles Gairdner Hospital (Western Australia), from 2013 to 2017.

Background: Coagulase-negative staphylococci such as S. epider-midis are part of human skin flora, however they commonly cause infections associated with peritoneal dialysis (PD). Peritonitis in PD patients can be life-threatening and these infections can be difficult to treat due to antimicrobial resistance (AMR). We investigated the prevalence of various AMR genes in S. epidermidis isolates collected over a 5-year period.

Methods: Isolates were cultured from PD effluent and identified using the MALDI-TOF. DNA was extracted using lysostaphin lysis followed by the Monarch Genomic DNA purification kit. Whole genome sequencing was performed on the NextSeq 500 Illumina platform. Raw sequence reads were assembled using SPAdes. The Resfinder database was used to identify AMR genes.

Results: 15 unique sequence types were identified with ST2 the most prevalent (29.6%) followed by ST6 (14.8%). The most commonly detected AMR genes were dfrC (100%), fosB (100%), mecA (74.1%), mupA (74.1%), aph(2″)-Ih (63.0%) and blaZ (56%) which confer resistance to trimethoprim, fosfomycin, methicillin, mupirocin, aminoglycosides, and penicillin, respectively. Conclusions: Many of the isolates displayed genotypic multidrug resistance, with resistance across a broad range of antimicrobial classes. With a high prevalence of the mupA gene, future studies need to address the implications of using mupirocin ointment as a preventative PD infection measure.