Aeromonas spp. from marketed Yesso scallop (Patinopecten yessoensis): molecular characterization, phylogenetic analysis, virulence properties and antimicrobial susceptibility

Abstract

Aims: Yesso scallop (Patinopecten yessoensis) is a popular seafood in Korea. Aeromonas spp., well-known pathogenic bacteria, has been reported in some molluscan shellfish, but it has not been studied in scallops so far. Therefore, we aimed to isolate, identify and characterize the Aeromonas spp. isolated from marketed Yesso scallops to estimate their potential risk to public health.

Methods and results: Thirty-two Aeromonas spp. including A. hydrophila (n = 13), A. salmonicida (n = 11), A. media (n = 3), A. caviae (n = 2), A. veronii (n = 2) and A. enteropelogenes (n = 1) were isolated from 105 marketed scallops and tested for phenotypic pathogenicity, virulence genes and antimicrobial susceptibility. Mean total bacterial count of scallop meat was 1·34 × 10⁴ CFU per gram. Slime production and lipase tests were positive in 97% of the isolates while DNase, protease, gelatinase, phospholipase and haemolysis were shown by 88, 88, 81, 88 and 72% of the isolates respectively. Eleven virulence genes were detected among Aeromonas spp. (act (75%), alt (59%), ast (47%), aerA (78%), lip (59%), ahyB (94%), ser (75%), hlyA (75%), fla (64%), gcat (84%) and ascV (23%)), and exu was negative in all isolates. Aeromonas hydrophila and A. salmonicida harboured ≥7 virulence genes and positive for enterotoxin genes, act, alt and ast. All the isolates were multidrug resistant and 100% resistant to ampicillin, colistin, vancomycin and cephalothin. Also, 30, 31, 20, 21, 29, 24, 27 and 27 of the isolates were resistant to piperacillin, clindamycin, erythromycin, nalidixic acid, imipenem, meropenem, trimethoprim-sulfamethoxazole and rifampicin respectively.

Conclusions: It is obvious with our results that the Aeromonas spp. isolated from Yesso scallops are highly virulent and potentially pathogenic, whereas the multidrug resistance further expedite their importance.

Significance and impact of the study: To our knowledge, this is the first study reporting Aeromonas spp. in scallop. This implies that not only the common varieties like oysters, but other bivalves can also harbour potentially pathogenic aeromonads which may have impacts on consumer health.

Keywords: gyrB; Aeromonas spp.; antimicrobial resistance; prevalence; scallop; virulence.