Investigations on Tetracycline Resistance in Commensal Escherichia Coli Isolates from Swine

The distribution of tetracycline resistance in commensal E. coli strains, isolated from pigs at different stages of production system was investigated in four Bulgarian swine farms. The prevalence of antibiotic resistance and particularly tetracycline resistance, as well as two tetracycline resistance genes were evaluated in Escherichia coli isolates from swine faeces and manure lagoons. A total of 109 E. coli isolates from 116 faecal samples and 7 samples from manure lagoons were tested by disk diffusion method to determine resistance patterns to 10 antimicrobial agents. Tetracycline resistance was determined by disk diffusion method, micro-broth dilution method and qPCR. About 83% of the E. coli isolates from swine were resistant to one or more antimicrobial agents, respectively. The highest resistance observed in swine E. coli isolates was that to tetracycline (75.2%). The resistant E. coli isolates to tetracycline were examined for the presence of tet genes: tet (A) and tet (B). The most commonly identified tet gene was tet (A), which was found in 96.4% of swine and manure lagoon isolates.