Multidrug-resistance in methicillin-resistant Staphylococcus aureus (MRSA) isolated from a subtropical river contaminated by nearby livestock industries

Methicillin-resistant Staphylococcus aureus (MRSA) is a major threat to public health that causes infections in hospitals, communities, and animal husbandry. Livestock-associated MRSA (LA-MRSA) is defined as MRSA possessing staphylococcal cassette chromosome mec (SCCmec) IV or V, both of which lacks the Panton–Valentine leukocidin (PVL) gene but has variable combinations of antimicrobial susceptibility. This study focused on Taiwan's subtropical river basin and the Puzih River, which converges from tributaries flowing through downtown and animal husbandry areas. MRSA was detected at a rate of 7.8% in the tributaries, which was higher than downstream (2.1%). The ratio of multidrug-resistant (MDR) MRSA (n = 30) to total MRSA isolates (n = 39) was 0.769, and most of the MDR MRSA isolates (66.7%, 20/30) exhibited resistance to chloramphenicol, ciprofloxacin, clindamycin, erythromycin, sulfamethoxazole-trimethoprim, and tetracycline. The number of MDR MRSA isolates in the tributaries was also higher than the downstream regions of the Puzih River. The majority of MRSA isolates (64.1%) observed in this study possessed SCCmec type IV without PVL, which is typical for LA-MRSA. Enterobacterial repetitive intergenic consensus PCR (ERIC-PCR) typing aided the discrimination of resistance patterns among SCCmec types. This study highlights the threat to human health posed by the waterborne transmission of MDR LA-MRSA.