ABSTRACT
The occurrence of pathogenic antimicrobial-resistant bacteria strains, including Escherichia coli and Listeria monocytogenes, in foods threatens the public health ecological space. Therefore, monitoring the emergence of resistant pathogens in seafood is particularly important. This study aimed to characterize the antimicrobial resistance of L. monocytogenes and E. coli coupled with their resistance and virulence genes distribution in processed readyto-eat (RTE) seafood. A total of 520 ready-to-eat seafoods were collected from April 2021 to January 2023 from shops and open markets in Bayelsa, Nigeria. The samples were subjected to L. monocytogenes and E. coli identification using physiological, culture-based methods, as well as polymerase chain reaction (PCR) methods. The isolates were screened for their susceptibilities to clinically relevant antimicrobials using the Kirby-Bauer method. Bacterial extracellular virulence enzymes, biofilm formation, and adherence capabilities were assessed using standard bacteriological techniques. Resistance and virulence genes of the isolates were also screened using PCR. From the 520 processed RTE seafood samples assessed, 37(7.1%) and 63(12.1%) were positive for the occurrence of L. monocytogenes and E. coli, respectively. Among the 63 E. coli isolates recovered from the processed seafood samples, 51(9.8%) were non-ESBL (extended-spectrum β-lactamase) producing E. coli, while 12(2.3%) were ESBL-producing E. coli. L. monocytogenes isolates were resistant to antimicrobials such as tetracycline 19(51.4%), levofloxacin 16(43.2%), and trimethoprim-sulfamethoxazole 13(35.1%). Multiple antibiotic-resistant index (MARI) of L. monocytogenes ranged from 0 – 0.62. Twenty-one (56.8%) L. monocytogenes isolates were multidrug resistant (MDR). Non-ESBL producing E. coli isolates were resistant to ampicillin 39(76.5%), gentamicin 32(62.7%), ciprofloxacin 24(47.1%), and chloramphenicol 27(52.9%). ESBL-producing E. coli isolates were completely 12(100%) resistant to ampicillin, piperacillin, amoxicillin-clavulanate, ampicillinsulbactam, ceftazidime, cefotaxime, and aztreonam; 7(58.3%) isolates were resistant to kanamycin, ciprofloxacin, and trimethoprim-sulfamethoxazole; 8(66.7%) isolates were resistant to gentamicin and tetracycline. The MARI of E. coli ranged from 0 – 0.71. Fifty-two E. coli isolates (82.5%) were MDR. The proportions of L. monocytogenes extracellular virulence factors formed include S-layer 24(64.9%), protease 22(59.5%), gelatinase 23(62.2%), lipase 25(67.6%), and lecithinase 19(51.4%). Extracellular virulence factors formed in E. coli includes curli 26(41.3%), cellulose 29(46.0%), protease 18(28.6%), β- xv hemolysis 9(14.3%), lipase 17(26.9%), and lecithinase 17(26.9%). L. monocytogenes hydrophobicity assay via bacterial adherence to hydrocarbon (BATH) were profiled as follows: hydrophilic 13(35.1%), moderately hydrophobic 19(51.4%), and strongly hydrophobic 5(13.5%). L. monocytogenes hydrophobicity via salting aggregation technique (SAT) showed hydrophilic 14(37.8%), moderately hydrophobic 18(48.6%), and strongly hydrophobic 5(13.5%). E. coli hydrophobicity via BATH revealed hydrophilic 30(47.5%), and moderately hydrophobic 33(52.4%); while SAT revealed hydrophilic 33(52.4%), moderately hydrophobic 14(22.2%), and strongly hydrophobic 16(25.4%). The proportions of antibiotic-resistance genes in L. monocytogenes include tetM 11(29.7%), cmlA1 8(21.6%), and qnrS 10(27.0%). Antibiotic resistance genes detected in E. coli includes tetM 21(33.3%), aadA 19(30.2%), ampC 34(53.9%), and qnrS 17(26.9%). The resistance genotypes of all isolates corresponded to the resistance phenotype. L. monocytogenes virulence genes detected included actA 33(89.2), hlyA 35(94.6), flaA 31(83.8), iap 22(59.5), inlA 8(21.6), inlB 8(21.6), and prfA 9(24.3). The occurrence of typical diarrhoeagenic E. coli in the seafood samples included tEAEC 4(6.3%), tEPEC 5(7.9%), tETEC 3(4.8%), and tEIEC 1(1.6%). Atypical diarrhoeagenic E. coli occurrences included aEAEC 10(15.9%), aEPEC 8(12.7%), aETEC 8(12.7%), aSTEC 4(6.3%), and aEIEC 6(9.5%). L. monocytogenes biofilm profile was strong in 9(24.3%) isolates, moderate in 11(29.7%) and poor in 17(45.9%). L. monocytogenes biofilms significantly positively correlated with S-layer (r=0.712, p<0.01), MARI (r=0.619, p<0.01), SAT (r=0.907, p<0.01), BATH (r=0.937, p<0.01), flaA (r=0.426, p<0.01), and perfA (r=0.540, p<0.01). The proportion of biofilm formation of the E. coli isolates includes strong 17(26.9%), moderate 14(22.2%), and poor 32(50.8%) formation. E. coli biofilms significantly positively correlated curli (r=0.615, p<0.01), cellulose (r=0.446, p<0.01), SAT (r=0.914, p<0.01), and BATH (r=0.922, p<0.01). Overall, this research contributes to our understanding of the presence, characteristics, and potential risks associated with antimicrobial-resistant bacteria, emphasizing the importance of monitoring and addressing these issues in the context of seafood safety and public health.
