Dissemination of Staphylococcus epidermidis in Swedish bovine dairy herds: minimal human overlap

The knowledge on zoonotic links between bovine and human isolates of Staphylococcus (S.) epidermidis is limited. The main aim of the present study was therefore to establish genetic relatedness, detection and comparison of genes encoding antimicrobial resistance (AMR) and virulence, of isolates originating from bovine cases of subclinical mastitis, bovine milk filters, human hospital patients, and healthy dairy farmers or farm personnel. A secondary aim was to study the epidemiology of bovine S. epidermidis intramammary infections (IMI) by analyzing associations between genotypes and geographic location, persistence of IMI and severity of inflammatory reaction as well as the persistence of S. epidermidis strains over time. A total of 283 isolates of S. epidermidis (SEP), 128 SCM milk isolates, 55 milk filter isolates, 13 farmer/personnel isolates and 87 human patient isolates, were analyzed using whole genome sequencing (WGS). A total of 60 unique sequence types (STs) of S. epidermidis were identified. ST99, ST100 and ST570 were most common among bovine isolates and ST2 and ST215 among human isolates. Only four STs (ST59, ST73, ST184 and ST218), identified in a total of 13 isolates, were found in both bovine and human samples. Presence of genes concurring AMR was more common in isolates from human patients compared to bovine isolates. However, resistance to penicillin, identified by presence of the blaZ gene was found in 42% of the bovine isolates of S. epidermidis. The average total number of potential virulence factors (pVF) detected per isolate was 23.8, with some variation in total numbers and presence of specific pVF or functional groups of pVF between sample types and STs. In conclusion, the results indicate that overlap of STs and AMR genes between humans and bovines was very limited. The results also generated new knowledge on the epidemiology of bovine S. epidermidis IMI with implications for the control of such infections.