Preliminary investigation of multiple antibiotic-resistant bacteria isolated from blood cockles (Anadara granosa) and green lipped mussel (Perna viridis)

Abstract

Aims: Bivalve molluscs are filter feeders that tend to accumulate and concentrate any suspended particles or bacteria from the water environment. Although they have been proven to accumulate heavy metals, investigation on the presence of antibiotic-resistant bacteria is still lacking. Therefore, this study examines the occurrence of antibiotic-resistant bacteria isolated from bivalve shellfish, namely, blood cockles (Anadara granosa) and green-lipped mussel (Perna viridis) purchased from markets in Johor, Malaysia. Methodology and results: Samples purchased were homogenized and then diluted. Viable cell count and bacterial isolation were performed using diluted samples followed by an antibiotic susceptibility test (ampicillin, ciprofloxacin and tetracycline) conducted on the pure isolates. The total viable count of bacterial colonies for cockle and mussel samples ranged from 1.1 × 107 to 4.4 × 109 CFU/mL and 1.2 × 109 to 4.3 × 109 CFU/mL. The numbers of colonies isolated from respective bivalves were 11 and 6. Generally, cockles isolates revealed higher resistance towards all three antibiotics at or above the Clinical and Laboratory Standard Institute (CLSI) threshold value. Meanwhile, mussel isolates showed full susceptibility to any ciprofloxacin concentration and tetracycline but exhibited resistance to ampicillin at a concentration exceeding the CLSI value. The number of drug resistance isolates in cockle and mussel samples decreased with increasing antibiotic concentration. The maximum number of antibiotics the mussel isolates were resistant to was two, whereas cockle isolates achieved three. Conclusion, significance and impact of study: The outcome of this study concludes that some isolates from cockle and mussel samples can resist antibiotic concentration above the CLSI threshold value. Resistance of more than the CLSI threshold level revealed that these isolates could pose significant health risks especially when the bivalves are ingested raw or undercooked.