Study On Reducing ?-Lactam Antibiotics Resistance Of E.coli From Swine Using Bacillus

In this study,185 strains of E.coli from pigs were tested for drug-sensitivity.Their sensitivity to typical ?-lactam antibiotics was tested,and highly resistant strain to ampicillin were screened out for the study of competition between resistant and sensitive strains.Exploratory test were carried out to mix probiotic bacillus with resistant and sensitive E.coli strains of ampicillin in the test tube or on the simulative piggery floors for coculture.And in this period,certain factors were artificially adjusted and some auxiliary measures were combined.to examine the ampicillin-resistant.The proportion of resistant E.coli strains in these two artificial environments were measured regularly.The study might provide a theoretical basis for finding ways to reduce the risk of drug-resistant bacteria in pig farms.1.Modified replica plating method was used to investigate effect of the initial proportion of ampicillin-resistant E.coli strain(G414),the type of probiotics,and the level of nutrition on the change of colony ratio of G414 in the artificial microflora.Results: The drug-resistant strain in the artificial community survived more competitively than the sensitive strain(ATCC 25922),and the proportion gradually increased from the 1st to 7th day;the proportion of resistant colonies in the highest initial proportion group increased from 33% to 64%,triumphed over sensitive strain and became the dominants in the community,when the lowest initial proportion increased from 10% to 43%;B.subtilis and B.licheniformis could significantly slow down the proportion of resistant strains in the community from the 1st to 7th day.With increasing trend(P<0.05),B.cereus could significantly reduce the proportion of drug-resistant colonies except for two days at the beginning(P<0.01);Under the highest(100%),medium(10%),and lowest(1%)nutrient condition,the proportion of resistant colonies gradually increased,and the proportion of the medium nutritional group rose fastest.Conclusion: The ampicillin-resistant E.coli strain did not increase its competitive fitness cost in the drug-free environment by carrying drug resistance genes,instead obtained certain competitive advantage under the conditions of normal nutrition,lower nutrition,and multi-species competition.The resistant E.coli gradually become dominant bacteria in the artificial community.If spread out,it may pose a greater threat to public health;B.subtilis and B.licheniformis could only reduce the increasing trend of the resistant colonies proportion,while B.cereus could very significantly inhibit the growth of drug-resistant colonies and prompt their extinction.They might reduce the number of certain resistant bacteria in the environment.2.Agar dilution method and pour plate culture method were applied to investigate effect of measures such as spraying B.cereus,washing+spraying B.cereus,disinfecting+spraying B.cereus,washing+disinfecting+spraying B.cereus.The resistance level of the ampicillin-resistant E.coli colonies(G414)and the corresponding proportion were detected within 15 days.Results: Overall,the proportion of ampicillin-resistant E.coli colonies in the test group decreased over time,and the decrease extent was different in some groups.Conclusion: Spraying B.cereus on the simulative ground alone may not significantly reduce the proportion of ampicillin-resistant E.coli colonies.There is a significant difference between the combined treatment and the control group(P<0.05).The glutaraldehyde of 1/2 MBC didn't have a significant effect on enhancing B.cereus.