Colistin Resistance inEscherichia coliandSalmonella entericaStrains Isolated from Swine in Brazil

Abstract

Reports about acquired resistance to colistin in different bacteria species are increasing, includingE. coliof animal origin, but reports of resistance in wildS. entericaof different serotypes from swine are not found in the literature. Results obtained with one hundred and twenty-sixE. colistrains from diseased swine and one hundred and twenty-fourS. entericastrains from diseased and carrier swine showed a frequency of 6.3% and 21% of colistin-resistant strains, respectively. When comparing the disk diffusion test with the agar dilution test to evaluate the strains, it was confirmed that the disk diffusion test is not recommended to evaluate colistin resistance as described previously. The colistin MIC 90 and MIC 50 values obtained toE. coliwere 0.25 μg/mL and 0.5 μg/mL, the MIC 90 and MIC 50 toS. entericawere 1 μg/mL and 8 μg/mL. Considering the importance of colistin in control of nosocomial human infections with Gram-negative multiresistant bacteria, and the large use of this drug in animal production, the colistin resistance prevalence in enterobacteriaceae of animal origin must be monitored more closely.