Prevalence of resistance to sulfonamides and streptomycin among commensal porcine Escherichia coli isolates

The aim of this study was to describe the prevalence of antibiotic resistance to streptomycin, spectinomycin and sulfamethoxazole and resistance genes aadA1, sul1, sul2, intI in Escherichia coli isolates from faeces and lagoon manure on seven swine farms in the Republic of Bulgaria. A total of 540 E. coli isolates isolated from 574 faecal samples and samples from manure lagoons were tested by disk diffusion method to determine resistance patterns to 11 antimicrobial agents and by the MIC plate method for streptomycin and sulfamethoxazole. The highest resistance in swine E.coli isolates was observed to streptomycin - 69.4% and spectinomycin - 63.3%. Multi-resistance patterns in studied E. coli strains showed that the resistance to streptomycin/spectinomycin was most frequently seen together with resistance to tetracycline, and sulfonamides (27.8%). The aadA1 gene was found in 54.4% of swine isolates and lagoon manure isolates. The sul1 gene was identified in 20.3% and sul2 gene in 21.2% of E. coli isolates. The prevalence of intI gene was determined in 9.8% of isolates. The presence of variable region of class I integrons with size 1 kb was found in 5.3% of E.coli isolates.