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Reports about acquired resistance to colistin in different bacteria species are increasing, including E. coli of animal origin, but reports of resistance in wild S. enterica of different serotypes from swine are not found in the literature. Results obtained with one hundred and twenty-six E. coli strains from diseased swine and one hundred and twenty-four S. enterica strains 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 to E. coli were 0.25 μg/mL and 0.5 μg/mL, the MIC 90 and MIC 50 to S. enterica were 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.

A disease named locally as churrío or churrido equino (i.e., equine scours) has occurred for at least 100 years in Uruguay and southern Brazil in farms along both shores of the Merín lake. This report describes cases of churrido equino and provides serologic, pathologic, and DNA-based evidence indicating that the disease is in fact equine monocytic ehrlichiosis (Potomac horse fever). Results of an epidemiological investigation conducted on an endemic farm are also presented. Clinical signs in 12 horses were fever, depression, diarrhea, dehydration, and sometimes colic and distal hind limb edema. Postmortem findings of 3 horses were of acute enterocolitis. Inclusion bodies containing ehrlichial organisms were found in the cytoplasm of macrophages of the large colon of 1 horse. Eleven of the 12 horses were serologically positive to Ehrlichia risticii (indirect fluorescent antibody assay) and, of 3 paired samples, 2 showed seroconversion. Ehrlichia risticii DNA was identified by a nested polymerase chain reaction in peripheral blood of an affected horse. A healthy horse inoculated with peripheral blood from an affected horse developed the disease and antibodies to E. risticii. The disease had a peak incidence in March (summer) and was statistically associated with a marshy ecosystem near the Merín lake, where large numbers of Pomacea spp. (Ampullariidae) snails were found. Incidence density was almost 8 times higher in nonnative horses than in native horses. It was concluded that the previous diarrheic disease of horses known in Uruguay and southern Brazil as churrido equino is equine monocytic ehrlichiosis.