Changes in antibiotic resistance trends (phenotype and genotype) of Salmonella isolated from pork at traditional markets in Hanoi

The study aims to analysis the trend of the phenotype and genotype resistance profiles of Salmonella isolates from pork collected in Hanoi traditional markets in 2018 and 2023 for commonly used antibiotics. The results showed a significant increase in the resistance rate of two antibiotics including ceftazidime (2.4% and 10.2%) and amoxicillin/clavulanic acid (0% and 35.6%) over five years (p<0.05). Salmonella spp. isolates in 2018 and 2023 were highly resistant to tetracycline (83.3% and 79.7%), sulfonamide (78.6% and 83.1%), ampicillin (71.4% and 67.8%), while were completely susceptible to imipenem and norfloxacin. However, the change in resistance to these antibiotics between the 2018 and 2023 isolates were not statistically significant. The study identified 2/110 (1.98%) colistin-resistant Salmonella isolates, of which the 2018 isolate carried gene mcr1, and the 2023 isolate carried gene mcr3. In addition, we found 7 Salmonella isolates with ESBL-producing phenotypes, of which 6/59 (10.2%) isolates were in 2018 and 1/42 (2.4%) isolate was in 2023. Of these, 5 isolates carried gene blaCTX-M, 2 isolates carried both the blaCTX-M and blaTEM, and no isolates carried the blaSHV. The research results provide scientific evidence showing the need to strengthen management and monitoring of antibiotic status to limit resistance rates and the spread of drug-resistant bacteria.