Identification and Characterization of Integron-Mediated Antibiotic Resistance among Shiga Toxin-Producing Escherichia coli Isolates

Abstract

A total of 50 isolates of Shiga toxin-producing Escherichia coli (STEC), including 29 O157:H7 and 21 non-O157 STEC strains, were analyzed for antimicrobial susceptibilities and the presence of class 1 integrons. Seventy-eight (n ‫؍‬ 39) percent of the isolates exhibited resistance to two or more antimicrobial classes. Multiple resistance to streptomycin, sulfamethoxazole, and tetracycline was most often observed. Class 1 integrons were identified among nine STEC isolates, including serotypes O157:H7, O111:H11, O111:H8, O111:NM, O103:H2, O45:H2, O26:H11, and O5:NM. The majority of the amplified integron fragments were 1 kb in size with the exception of one E. coli O111:H8 isolate which possessed a 2-kb amplicon. DNA sequence analysis revealed that the integrons identified within the O111:H11, O111:NM, O45:H2, and O26:H11 isolates contained the aadA gene encoding resistance to streptomycin and spectinomycin. Integrons identified among the O157:H7 and O103:H2 isolates also possessed a similar aadA gene. However, DNA sequencing revealed only 86 and 88% homology, respectively. The 2-kb integron of the E. coli O111:H8 isolate contained three genes, dfrXII, aadA2, and a gene of unknown function, orfF, which were 86, 100, and 100% homologous, respectively, to previously reported gene cassettes identified in integrons found in Citrobacter freundii and Klebsiella pneumoniae. Furthermore, integrons identified among the O157:H7 and O111:NM strains were transferable via conjugation to another strain of E. coli O157:H7 and to several strains of Hafnia alvei. To our knowledge, this is the first report of integrons and antibiotic resistance gene cassettes in STEC, in particular E. coli O157:H7.

Antimicrobial Resistance Genes in Enterotoxigenic Escherichia coli O149:K91 Isolates Obtained over a 23-Year Period from Pigs

“…Most class 1 integrons in the E. coli isolates in our collection contained VRs of 1.3 and 1 kb. The VRs of integrons found in Shiga toxinproducing E. coli isolates were of similar sizes (36). Interestingly, an increase in the VR length was observed in E. coli strains isolated during the last period, a phenomenon also observed by Schmitz et al (28).…”

Detection of Several Virulence Properties, Antibiotic Resistance and Phylogenetic Relationship in E. Coli Isolates Originated from Cow Mastitis

“…E. coli is an environmental mastitis pathogen, which causes clinical signs in mammary glands in cows and its resistance against antibiotics depends on herd management. In previous studies, various antibiotic resistance profi les and rates in E. coli strains were stated in previous studies especially for oxytetracycline [29,30,31,32], penicillin [22,32,33,34], macrolides [21,35,36], trimethoprimsulphamethoxazole [6,36,37], fl uoroquinolones [35,36] and cephalosporins [38]. In the presented papers, resistance profi les of E. coli strains were evaluated for vancomycine, danofl oxacin, oxytetracyline, enrofl oxacin, amoxicillin-clavulanic acid, trimethoprim-sulphamethoxazole, ampicillin and tetracycline.…”

Isolation, characterization and complete genome sequence of PhaxI: a phage of Escherichia coli O157 : H7

“…It is estimated that the recent emergence of antibioticresistant E. coli O157 : H7 is due to the use of antibiotics for prophylaxis or growth promotion in food animal production (Galland et al, 2001;Schroeder et al, 2002;Zhao et al, 2001). Antibiotic resistance is a serious complication in the treatment of infections (Mizoguchi et al, 2003;O'Flynn et al, 2004).…”

“…Antibiotic therapy at early stages of infection seems to prevent haemolytic uraemic syndrome development; however, the efficacy of antibiotic therapy is uncertain (Zhao et al, 2001). Some antibiotics induce the expression of Shiga toxin genes or disrupt bacterial cell walls and cause the release of Shiga toxins (Galland et al, 2001;Schroeder et al, 2002 ;Zhao et al, 2001).…”

“…Some antibiotics induce the expression of Shiga toxin genes or disrupt bacterial cell walls and cause the release of Shiga toxins (Galland et al, 2001;Schroeder et al, 2002 ;Zhao et al, 2001).…”