Tyler Gerken

Project title: Environmental Surveillance and Characterization of Antibiotic Resistant Staphylococcus aureus at Coastal Beaches and Rivers on the Island of Hawaiʻi

Degree: MS (Thesis) | Program: Environmental Health (EH) | Project type: Thesis/Dissertation
Completed in: 2021 | Faculty advisor: Marilyn C. Roberts


Staphylococcus aureus are both human commensal bacteria and potential pathogens. The aim of this study was to isolate and characterize methicillin-resistant Staphylococcus aureus (MRSA) and methicillin-susceptible S. aureus (MSSA) from coastal beach and river waters, anchialine pools, sand, and wastewater on the Island of Hawaiʻi, Hawaiʻi. A total of 361 samples were collected from three regions on the Island from June to December 2020 during the COVID-19 pandemic. From these samples, 98.1% were positive for Staphylococcus spp. and 7.2% were S. aureus positive. Thirty-six S. aureus isolates (nine MRSA and 27 MSSA) were characterized using whole-genome sequencing (WGS). The MRSA isolates were multi-drug resistant ST8 (CC8) SCCmec type IVa, carrying 6–9 different antibiotic resistance genes, 16–19 virulence factors, and were clonally related (0–16 SNP differences). The 27 MSSA isolates were grouped into eight clonal complexes (CC) and 12 sequence types (ST). A higher proportion of MRSA was identified in sand compared to water samples (8.6% vs. 1.6%, respectively). Seventy-eight percent of the MSSA isolates carried 1–5 different antibiotic resistance genes with blaZ being the most common. All MSSA carried 5–19 virulence factors. Both the MRSA and MSSA STs have previously been associated with human, animal, and/or environmental samples globally. Our results demonstrate a potential public health hazard at public beaches in Hawaiʻi with limited human activity.

URI: http://hdl.handle.net/1773/47486