Detection And Analysis Of Fluoroquinolone Resistance And Resistance Genes In Bacteria Isolated From Tilapias In Supermarkets

A lot of research shows,the long-term use of antibiotics in animal husbandry and aquaculture has led to emergence of resistant strains.The resistant bacteria carried by farmed animals can transmit their resistance and resistance genes to humans through direct contact,food chain and environmental pollution.It poses a serious threat to human health,which has constituted a huge worldwide public health problem.Fluoroquinolones are a class of synthetic antibiotics,due to its broad spectrum,excellent pharmacokinetic properties,strong antibacterial activity,and lack of cross-resistance with other antibiotics,it has been widely used in the aquaculture industry.China’s aquaculture production ranks first in the world,and aquatic products have become an important part of people’s daily food.Therefore,it is of great significance to conduct in-depth studies on the bacteria carried by aquatic products on the resistance to fluoroquinolones and the carrying and mutation of drug resistance genes,which can provide a scientific basis for food safety supervision and monitoring.This study uses commercially available tilapia fishery products as research objects.We randomly purchased 100 live tilapia products from 14 supermarkets in Guangzhou,highthroughput sequencing method was used to analyze its dominant bacteria,determination of fluoroquinolone susceptibility of dominant bacteria carried by agar double dilution method.After boiled bacterial DNA was extracted,PCR amplification was used to detect and analyze bacterial PMQR gene carriage rate and QRDR mutations.The aim is to accumulate scientific data for risk assessment of drug-resistant bacteria and drug resistance genes carried in aquatic products and provide scientific basis for food safety monitoring.The dominant bacteria in commercially available tilapia commercial fish were Aeromonas and Escherichia coli,and a total of 280 Aeromonas and 182 E.coli were isolated.The number of Aeromonas isolated from different tissues was similar,and the isolated E.coli was mainly derived from cockroaches and intestinal tissue.Aeromonas resistant rates to enrofloxacin and ciprofloxacin were 2.50% and 2.14%,respectively.The resistance rates of E.coli to enrofloxacin and ciprofloxacin were 25.82% and 18.13%,respectively.The resistance rate of E.coli to test drugs was higher than that of Aeromonas.The resistance rate of bacteria isolated from different tissues was different,and the resistance rate of bacteria isolated from muscle was the lowest.Only qnrS and aac(6’)-Ib-cr were detected from Aeromonas,the carrier rates were 4.29% and 2.86%,respectively.Five kinds of PMQR genes including qnrB,qnrS,aac(6’)-Ib-cr,oqxAB and qnrD were detected from E.coli,the carrier rates were 12.64%,36.81%,9.89%,11.54% and 0.55%,respectively.The PMQR gene carrying rate of E.coli was higher than that of Aeromonas salmonella PMQR gene,and there were many species.The results of the QRDR target gene mutation showed that 98 of the 103 strains of Aeromonas that had a mutation in the QRDR target gene had a gyrA gene mutation.5 strains only had parC gene mutations,41 of them had gyrA and parC double mutations,and gyrA mutations were found in 41 of 60 E.coli strains that had a mutation in the QRDR target gene,parC mutation occurred in 19 strains,17 of them had double mutations in gyrA and parC genes.The results showed that the predominant bacteria in each tissue of commercial tilapia fishery products were Aeromonas and E.coli.E.coli were more resistant to enrofloxacin and/or ciprofloxacin than Aeromonas.The resistance rates of Aeromonas and E.coli isolated from muscle to enrofloxacin and/or ciprofloxacin were lower than those of gills and gut.It shows that the edible part of tilapia is very few and the food is relatively safe.However,E.coli is the main drug-resistant bacteria carried by the gut and gill tissues,and most of the strains carry different types of PMQR genes,and there is a certain risk of spread of drug resistance.the study on the resistance mechanism of bacteria to fluoroquinolones found that the gene mutation of Aeromonas QRDR mainly occurs in the gyrA gene.The QRDR target gene mutation and the PMQR gene play an integral role in Aeromonas fluquinolone drug resistance and are indispensable.Aeromonas and E.coli have different fluoroquinolones resistance mechanisms.In addition,a comparative analysis of the correlation between E.coli and Aeromonas bacteria carrying the PMQR gene,QRDR gene mutations,and resistance phenotypes revealed that the resistance mechanisms of the two fluoroquinolones may be different for the two bacteria.The specific differences need further study.