Antimicrobial resistance and resistance gene determinants of fecal Escherichia coli isolated from chicken

Antimicrobial resistance has emerged as a major problem and national antimicrobial resistance management program has been set up for antimicrobial resistance surveillance in human and veterinary medicine from 2009 in Korea. The aim of the present study was to assess the actual frequency of antimicrobial resistance in fecal Escherichia coli (E. coli) isolated from chicken at the phenotype level and to determine the genetic background for the two major resistance phenotypes (Streptomycin and tetracycline). One hundred and nine E. coli isolates were higher resistant to ampicillin (68.8%), cephalothin (63.3%), streptomycin (60.6%), ciprofloxacin (65.1%), enrofloxacin (79.8%), norfloxacin (66.1%), tripmethoprim/sulfamethoxazole (50.5%), erythromycin (89.0%) and tetracycline (96.3%). All of them showed resistance to two or more of the 18 antibiotics tested and one isolates was resistant to 13 antibiotics. In 51 (46.8%) isolates of 105 tetracycline resistant isolates only the resistant gene tetA was amplified while both the tetA and tetB gene were found in 22 (20.2%) isolates. The only tetB gene was found in 11 (10.1%) isolates and tetA and tetC gene was found in two isolates. About 30 (27.5%) isolates among 66 streptomycin resistant isolates were positive with strA, strB and aadA gene. The 25 (22.9%) and 4 (3.7%) isolates were positive with strA plus strB and strB plus aadA gene, respectively. The researchers could show that significant differences can be observed between isolates not only at the phenotype level but also at the genotype level.