Mesophilic Aeromonas spp. isolated from live Manila clam (Ruditapes philippinarum): virulence properties and multidrug resistance

This study aimed to evaluate the virulence determinants and multidrug resistance properties of mesophilic Aeromonas isolated from live Manila clams marketed in Korea. A total of 36 Aeromonas spp., comprising eleven A. hydrophila, eleven A. salmonicida, seven A. media, four A. veronii, two A. allosaccharophila, and one A. caviae isolate, were used in this study. The most common virulence traits observed were DNase and phospholipase activity, which were present in 100% of tested isolates, followed by gelatinase (94%), lipase (83%), hemolysis (78%), caseinase (75%), and slime production (31%). High prevalence of virulence genes; ahyB, fla, hlyA, gcat, ast, lip, ser, aerA, ascV, act, and alt, was identified in polymerase chain reaction (PCR) assay. Three A. hydrophila and seven A. salmonicida isolates were positive for all tested virulence genes. In contrast, three enterotoxin genes (alt/ast/act) were observed in A. salmonicida, A. hydrophila, and A.veronii. Alarmingly, in our study, 97% of Aeromonas isolates had MAR (multiple antibiotic resistance) values >0.2, indicating that they are from sources with a high risk of antibiotic-resistant contamination. Statistically significant differences were found between the frequency of virulence genes among Aeromonas spp. as well as the frequency of antibiotic resistance among Aeromonas spp. (p < 0.05). The incidence of potentially virulent and enterotoxigenic Aeromonas spp. showing multidrug resistance raises concern regarding the potential health risks of consuming raw or undercooked Manila clams.