| The epibiotic lactic acid bacteria(LAB) on the surface of vegetables were commonly recognized as safe for a long time. In recent years, more and more antibiotic-resistant lactic acid bacteria were detected. The main threat associated with these LAB was that they may receive resistance genes from other bacteria or transfer resistant genes to pathogentic bacteria on human gastrointestinal tract. Organic vegetables were grown in accordance with the strict standard, which were considered safe. However, antibiotic resistance of lactic acid bacteria was detected in organic fertilizer, soil and water, and organic vegetables were attached to antibiotic resistance of lactic acid bacteria inevitably. The presence of the antibiotic resistance in the organic vegetable revealed the food safe risk, especially for the ready-to-eat fresh organic vegetable.The epibiotic LAB on the surface of organic radish were investigated by MRS culture,physiological and biochemical characteristics, RAPD and 16S rRNA. Approximately 4.67 ×103 CFU/cm2 LAB including 187 isolates colonized on the surface of organic white radish.These isolates were assigned to Pediococcus pentosaceus(114/187), Weissella cibaria(9/187), Leuconostoc mesenteroides(18/187), Leuconostoc pseudomesenteroides(7/187),Leuconostoc citreum(20/187) and Leuconostoc holzapfelii(19/187), respectively.The minimal inhibitory concentration(MIC) of LAB was determined by using microbroth dilution method. The European Committee on antimicrobial susceptibility testing gives different antibiotic sensitivity threshold to different bacteria. The epibiotic LAB on the surface of organic radish were investigated by antibiotic resistance and phenotype polymorphism. Among the 187 LAB strains, 35(18.72%) isolates displayed the solo-drug or multi-drug resistance of ampicillin(AMP), chloramphenicol(CHL), streptomycin(STR) and tetracycline(TET). And there were 6 solo resistances(3.2%), 13 double resistances(6.95%)and 16 triplicate resistances(8.56%). Among the 187 LAB strains, all isolates were found sensitive to erythromycin(ERY) and 3.74%(7/187) were resistance to AMP, CHL at 9.09%(17/187), STR at 13.9%(26/187), TET at 16.04%(30/187).All the antibiotic-resistance strains were tested for the presence of antibiotic resistance genes most frequently occurring in LABs by PCR amplification. Among the 35antibiotic-resistance LABs strains, the efrA gene and efrB gene belonged to ATP-binding cassette family were detected at 80% simultaneously. The acrA gene and acrB gene belonged to resistance-nodulation-division family were detected at 22.86% simultaneously, and the tolC gene was detected at 94.29%. The sugE gene belonged to small multidrug resistance family was detected at 77.14%. The norB gene belonged to major facilitator superfamily was detected at 14.29%. The norC gene belonged to major facilitator superfamily and located onchromosome was detected at 82.86%. The mdfA gene was detected at 65.71%. The sdrM gene belonged to major facilitator superfamily was detected at 17.14%. The norE gene belonged to multidrug and toxic efflux family was detected at 28.57%.Among the 30 TET resistance LABs strains, the detection rate of tetA gene, tetB gene,tetC gene, tetD gene, tetE gene, tetG gene, tetJ gene and tetK gene was 50%, 93.33%, 66.67%,80%, 36.67%, 86.67%, 50% and 86.67%. And these genes encode tetracycline efflux protein.The detection rate of tetO gene, tetQ gene, tetS gene, tetM gene and tetW gene which encode tetracycline ribosomal protection protein was 53.33%, 86.67%, 93.33%, 36.67% and 100%.And the detection rate of tetX gene was 26.67%.Among the 26 STR resistance LABs strains, the detection rate of strA gene, strB gene,aadA gene, aph(3')-IIIa gene and aac(6')-aph(2'') gene was 50%, 84.62%, 76.92%, 80.77%and 50%.Among the 2 AMP resistance LABs strains, P. pentosaceus LCB184 was observed to contain the bla and blaZ gene simultaneously, and P. pentosaceus LCB176 was only observed to contain the bla gene. |
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