| Listeria monocytogenes?LM?is a causative agent of Listeriosis.LM can cause gastroenteritis,sepsis,meningitis,abortion and other diseases through cross the intestinal barrier,the blood-fetal barrier and the blood-brain barrier.Susceptible populations include immunocompromised patients,the elderly,pregnant women and newborns and mortality rate can reach 2030%.Listeriosis in human is often associated with the consumption of raw or ready-to-eat foods contaminated with LM.With the irregular and abuse usage of antibacterial drugs in clinic,the resistance level of many LM isolates is gradually increasing.Drug-resistant strains will have a great impact on the treatment of the Listeriosis.Objective:The purpose of this study is to investigate the food contamination by LM,detect the drug resistance spectrum and drug resistance genes of food-borne LM in Xinjiang,and provide important reference data for guiding the rational application of antibiotics in human and animal clinical treatment and controlling the spread of drug resistance genes.Methods:The GB4789.30-2016 method was used to isolate and identify LM from 1222 food samples in Xinjiang.The Micro-broth dilution method and K-B agar diffusion method were used to determine the sensitivity of 18 antibiotics;Part of the related drug resistance genes were detected by PCR,and then localized and sequenced.Horizontal transfer of resistance gene tetM and ermB of LM were performed by membrane conjugation test between LM and Enterococcus.Results:A total of 61 LM strains were isolated from 1222 food samples in xinjiang,with a total detection rate of 4.99%?61/1222?.The detection degree of LM was higher in raw poultry meat,prepared meat products and animal aquatic products,with detection rates of 23.07%?18/78?,14.39%?19/132?and10%?6/60?,respectively.The Susceptibility tests showed that the resistance rate of 29.51%?18/61?detected by Micro-broth dilution method was higher than that of 21.31%?13/61?detected by K-B agar diffusion method.The resistance rate of tetracycline,streptomycin and compound xinnomin was higher than that of doxycycline and kanamycin.Three chloramphenicol-resistant strains,two erythromycin-resistant strains and one cefalotin-resistant strain detected by the Micro-broth dilution method were not detected by the K-B paper method.The drug resistance genes of 61 LM isolates were detected by PCR.The results showed that 65%?13/20?resistant phenotype strains were detected the corresponding drug resistance genes.The tetracycline resistance genes were mainly tetM,the erythromycin resistance gene is ermB,and the chloramphenicol resistance gene is cat.Among the 41 non-resistant phenotype strains,the detection rates of aminoglycoside resistance gene aac?6'?-Ib-cr and erythromycin resistance gene ermB were as high as 57.9%and 39.5%,respectively.The amplified fragment nucleotide sequences had homology of 95 to 100%with the reference sequences.The resistance gene localization revealed that tetM,tetA mainly existed in chromosomal DNA,tetS,cat and ermB mainly existed on the plasmid,while aac?6'?-Ib-cr was distributed on chromosome and plasmid.Two tetracycline-resistant strains and one erythromycin-resistant strain of LM were used as donors for conjugation with Enterococcus.17,23,and 28 transconjugants were obtained and the conjugation transfer rates were 3.4×107,4.6×107,5.6×107,respectively.The ermB or tetM gene of transconjugants was positive,and its sequence was consistent with the resistance gene sequence of donors.The drug sensitivity test of transconjugants showed resistant to tetracycline or erythromycince,respectively.Thease results indicated that the resistance gene ermB or tetM of LM could be transferred to Enterococcus horizontallyConclusion:In Xinjiang,food is contaminated by LM in different degrees.Some foodborne LM isolates showed drug resistance,and the drug resistance phenotype was not completely consistent with carrying of the drug resistance genes.The LM drug resistance genes tetM and ermB could be interspecies transferred horizontally. |
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