Antibiotic Resistance and Virulence Gene Characteristics of Methicillin-Resistant<i>Staphylococcus aureus</i>(MRSA) Isolated from Healthy Edible Marine Fish

Abstract

Thirty-three (33) isolates of methicillin-resistant <i>Staphylococcus aureus</i> (MRSA) from healthy edible marine fish harvested from two aquaculture settings and the Kariega estuary, South Africa, were characterised in this study. The phenotypic antimicrobial susceptibility profiles to 13 antibiotics were determined, and their antibiotic resistance determinants were assessed. A multiplex PCR was used to determine the epidemiological groups based on the type of SCC<i>mec</i> carriage followed by the detection of staphylococcal enterotoxin-encoding genes <i>sea</i>-<i>sed</i> and the Panton Valentine leucocidin gene (<i>pvl</i>). A high antibiotic resistance percentage (67-81%) was observed for Erythromycin, Ampicillin, Rifampicin, and Clindamycin, while maximum susceptibility to Chloramphenicol (100%), Imipenem (100%), and Ciprofloxacin (94%) was recorded. Nineteen (58%) of the MRSA strains had Vancomycin MICs of ≤2 <i>μ</i>g/mL, 4 (12%) with MICs ranging from 4-8 <i>μ</i>g/mL, and 10 (30%) with values ≥16 <i>μ</i>g/mL. Overall, 27 (82%) isolates were multidrug-resistant (MDR) with Erythromycin-Ampicillin-Rifampicin-Clindamycin (E-AMP-RIP-CD) found to be the dominant antibiotic-resistance phenotype observed in 4 isolates. Resistance genes such as <i>tetM</i>, <i>tetA</i>, <i>ermB</i>, <i>blaZ,</i> and <i>femA</i> were detected in two or more resistant strains. A total of 19 (58%) MRSA strains possessed SCC<i>mec</i> types I, II, or III elements, characteristic of healthcare-associated MRSA (HA-MRSA), while 10 (30%) isolates displayed SCC<i>mec</i> type IVc, characteristic of community-associated MRSA (CA-MRSA). Six (18%) of the multidrug-resistant strains of MRSA were enterotoxigenic, harbouring the <i>see, sea,</i> or <i>sec</i> genes. A prevalence of 18% (6/33) was also recorded for the <i>luk-PVL</i> gene. The findings of this study showed that marine fish contained MDR-MRSA strains that harbour SCC<i>mec</i> types, characteristic of either HA-MRSA or CA-MRSA, but with a low prevalence of enterotoxin and <i>pvl</i> genes. Thus, there is a need for continuous monitoring and implementation of better control strategies within the food chain to minimise contamination of fish with MDR-MRSA and the ultimate spread of the bug.