Changes In Norfloxacin Resistance After Co-culture Of Lactic Acid Bacteria With Escherichia Coli

In the experiment,9 strains of lactic acid bacteria were isolated from natural fermented dairy products in Siziwangqi Banner and Darhan Muminggan Joint Banner,Inner Mongolia and then co-cultured with Escherichia coli.The tube doubling dilution method was used to determine the minimal inhibitory concentration(MIC)of the co-cultured strains to clinical antibiotics of norfloxacin to observe the changes of drug resistance of the strains to norfloxacin before and after co-culture and to determine the factors influencing the drug resistance.The results showed that 18 strains of lactic acid bacteria and 18 strains of Escherichia coli were isolated from different culture medium after co-culture.Changes were found in the MIC values of the lactic acid bacteria.The MIC values of 4 strains increased,the MIC values of 6 strains of bacteria were not changed and the MIC values of 8 strains decreased.However,all the drug phenotypes were not changed and showed drug resistance.Changes were also found in the MIC values of isolated Escherichia coli.The MIC values of 4 strains increased,the MIC values of 5 strains of bacteria were not changed and the MIC values of 9 strains decreased.The resistance phenotypes of 3 strains including MRS-HZ18-DC,MRS-B26-DC and LB-B26-DC changed from drug resistant strains to the sensitive strains,while the resistance phenotypes of other strains had no change.The drug-resistant test with different pH values and different culture media,the test simulating gastrointestinal drug resistance,the physiological and biochemical test and 16SrRNA homology analysis were performed on the strains with changes in resistance phenotype.The results showed that different culture media and different pH values had certain effects on the resistant strains and the test strains were sensitive to norfloxacin in human gastric juice.However,in artificial intestinal juice,lactic acid bacteria had drug-resistance to norfloxacin and Escherichia coli had intermediary drug-resistance to norfloxacin.The physiological and biochemical phenotypes of the strains with changes in drug resistance changed with different degrees.The 16SrRNA homology analysis showed that MRS-HZ18-DC,MRS-B26-DC and LB-B26-DC had 98.2%homology compared with the standard strain DC(ATCC25922).The gene fragment sequences of the strains were not changed after co-culture.