Th e aim of this study was to describe the prevalence of antibiotic resistance to some aminoglycosides, streptomycin, spectinomycin and gentamicin
and three aminoglycoside- resistance genes in Escherichia coli isolated from feces and lagoon manure in six swine farms in Republic of Bulgaria. A
total of 274 E. coli isolates from 270 fecal samples and twelve samples from lagoon manure were tested by disk diff usion method to determine resistance patterns to 11 antimicrobial agents. Aminoglycosides resistance also was determined by E-test, agar dilution method, PCR and qPCR. Th e highest resistance observed to streptomycin (70.0%) and spectinomycin (65.5%). Multi-resistance patterns in studied E. coli strains showed that the resistance to streptomycin/spectinomycin was most frequently seen together with resistance to ampicillin, tetracycline, and sulfonamides (39.6%). The E. coli isolates resistant to streptomycin, spectinomycin were examined for the presence of strA/strB, aadA1 genes, and resistant isolates to gentamicin were evaluated for the presence of the aacC1 gene. Th e most common gene determining resistance to aminoglycosides was aadA1 which was found in 54.0% of swine isolates and lagoon manure isolates followed by straA/strB genes (32.3%). Th e aacC1gene was not identifi ed in E. coli isolates resistant to gentamicin.
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