Diversity among isolates of Staphylococcus intermedius group from Pacific marine mammals of Southern California

This study investigated the carriage of Staphylococcus (S.) intermedius group (SIG) isolates in marine mammals in the Pacific coastal region of Southern California, USA. We screened 452 samples from the oral cavities of California sea lions (Zalophus californianus), northern elephant seals (Mirounga angustirostris), harbor seals (Phoca vitulina), northern fur seals (Callorhinus ursinus), Guadalupe fur seals (Arctocephalus townsendi), long beaked common dolphin (Delphinus delphis bairdii), Pacific white-sided dolphins (Sagmatias obliquidens), and pygmy sperm whales (Kogia breviceps). Forty-two S. pseudintermedius and four S. delphini were obtained. Isolates were characterized by a polyphasic approach, which included antimicrobial susceptibility testing, molecular identification and characterization by rpoB/nuc sequencing, PCRs, DNA-based microarray, genotyping via spa and MLVA, and whole-genome sequencing of selected isolates. Resistance to penicillin, penicillin/tetracycline, and tetracycline alone was observed. Spa typing resulted either in novel types or in isolates that were non‑typeable. Twenty-nine MLVA types were detected. Multi-locus sequence typing revealed four STs: ST453 (previously described) and three novel STs: ST3046-8) among S. pseudintermedius and various virulence-associated genes were detected. Long-term monitoring remains essential to fully map its epidemiology, pathogenicity, and evolution of SIG in marine mammals.