C20 | Comparative analysis of phenotypic and genotypic (WGS) antimicrobial resistance in strains of Escherichia coli and Vibrio isolated from mussels sampled in the Campania region

V. Vuoso¹, R. L. Ambrosio¹, A. Alvarez-Ordóñez², E. Fernández -Trapote², M.F. Peruzy¹, A. Anastasio¹. | ¹Dip. di Medicina Veterinaria e Produzioni Animali, Università degli Studi di Napoli Federico II, Napoli, Italia; ²Dep. of Food Hygiene and Technology, Institute of Food Science and Technology, Universidad de León, León, Spain.

Purpose. The aim of the study was to evaluate the degree of antimicrobial resistance of Escherichia coli and Vibriostrains isolated from mussels from sales outlets and farms located in the Campania region. Eleven multidrug-resistant strains were selected, five E. coli and six Vibrio, most of which showed resistance to carbapenems following Kirby-Bauer phenotypic antibiotic susceptibility testing (23 antibiotics for E. coli and 10 for Vibrio, according to the guidelines of the European Committee on Antimicrobial Susceptibility Testing, EUCAST). Methods. Genomic DNA was extracted using the Quick-DNA™ Miniprep Plus Kit (Zymo Research) and sequenced using Illumina paired-end with an average coverage of ≥100×. Bioinformatic analyses allowed the identification of genes associated with antimicrobial resistance using the ResFinder and CARD databases, as well as the identification of related genetic structures. Results. No carbapenemase-encoding genes were detected in any of the E. coli strains analysed, suggesting that the observed resistance to carbapenems may be attributed to alternative mechanisms, in particular active efflux. This hypothesis is supported by the widespread presence of efflux pumps such as AcrAB-TolC, EmrAB and MdtFGH, often located in proximity to mobile genetic elements (MITEEc1, ISEc1, ISEsa1) potentially involved in their regulation or mobilisation. Genes associated with resistance to other classes of antimicrobials have also been identified, including blaEC-5, blaEC-18, blaCARB-42, bla-ampC, FosA, tet(A) and tet(35). No carbapenemase-encoding genes were detected in Vibrio strains (identified as V. alginolyticus, V. diabolicus and V. parahaemolyticus). In addition, these strains also showed phenotypic resistance to fluoroquinolones, tetracyclines, macrolides and β-lactams. The genomic profiles of Vibrio revealed the presence of resistance determinants frequently associated with mobile elements such as ISVpa3, ISVal1 and ISVa6. Among the genes located in proximity to these elements are blaCARB-57 and tet(35), consistent with the phenotypic resistance observed. In addition, the type III secretion system (T3SS) was found to be widespread, and its potential involvement in modulating the antimicrobial response requires further investigation. Conclusions. The integration of phenotypic and genotypic data has revealed unconventional resistance mechanisms: in E. coli strains, the overexpression of efflux pumps seems to play a central role, while in Vibrio, greater genetic complexity is observed, associated with the presence of mobile determinants and other accessory factors. However, no classic resistance genes have been identified in several resistant strains, suggesting the existence of alternative or as yet uncharacterised mechanisms. The results obtained suggest the importance of an integrated approach for effective surveillance of antimicrobial resistance and for a deeper understanding of the mechanisms emerging in foodborne microorganisms.