Association Of Mutation Patterns In ParC Genes And Quinolone Resistance Levels In Lactic Acid Bacteria

15lactic acid bacteria strains isolated from natural fermented koumiss in Xilin Gole in Inner Mongolia, were investigated in the present study. Firstly, experiments of morphology, physiological and biochemical characteristics, and molecular biology were carried on the tested strains. The results indicated that all of the15tested strains possessed several excellent characteristics, such as certain tolerance of salt resistance, heat resistance and bile tolerance which showed vigorous growth in6.5%saline, pH4.5-9.6. Then experiment of16S rRNA sequence analysis were carried on in the study. Combined the results of physiological and biochemical identification, there were4strains belonged to Enterococcus dispar,2strains belonged to Enterococcus raffinosus,2strains belonged to Enterococcus gilvus,1strain belonged to Enterococcus italicus,1strain belonged to Enterococcus villorum, and1strain belonged to Enterococcus durans.Three methods were used to test the15lactic acid bacteria strains’susceptibility to quinolone. The results showed that there were significant differences (P<0.05) between the Oxford cup method and Disk diffusion method, Drilling method. No significant difference were discovered between Disk diffusion method and Drilling method. The average value of SD (standard deviation) of the three methods presented that Disk diffusion method> Oxford cup method> Drilling method, which indicated that the Disk diffusion method showed poor reproducibility for whose experimental error was too large while the Drilling method showed the highest accuracy for its error was the smallest. Therefore, Drilling method can be applied to the detection of lactic acid bacteria susceptibility to quinolones.The15lactic acid bacteria strains demonstrated various levels of resistance to ofloxacin and norfloxacin when Drilling method and Disk diffusion method were used. Among them there are6drug resistant strains and8sensitive strains. The other strain, NN, showed quinolone resistance when Drilling method was used, while moderately sensitive when Disk diffusion method was used. However, in the MIC (minimal inhibitory concentration) test in which double tube dilution method was used, the incidences of resistance to these two quinolone were different, too. As for ofloxacin,3strains behaved moderately sensitive, and the other strains showed drug-resistant. To norfloxacin,1strain behaved sensitive while other strains showed drug-resistant.Futhermore, PCR amplification and gene sequencing test were conducted on parC of topoisomerase IV of these isolated strains. The results indicated that neither quinolone resistant strains, moderately sensitive strains nor sensitive strains shared the same genes of parC in QRDR which clearly demonstrated that there were no direct correlation between mutation patterns in parC genes and quinolone resistance levels in lactic acid bacteria.