Incidence and Characterization of Integrons, Genetic Elements Mediating Multiple-Drug Resistance, in Avian Escherichia coli

Abstract

Antibiotic resistance among avian bacterial isolates is common and is of great concern to the poultry industry. Approximately 36% (n ‫؍‬ 100) of avian, pathogenic Escherichia coli isolates obtained from diseased poultry exhibited multiple-antibiotic resistance to tetracycline, oxytetracycline, streptomycin, sulfonamides, and gentamicin. Clinical avian E. coli isolates were further screened for the presence of markers for class 1 integrons, the integron recombinase intI1 and the quaternary ammonium resistance gene qacE⌬1, in order to determine the contribution of integrons to the observed multiple-antibiotic resistance phenotypes. Sixty-three percent of the clinical isolates were positive for the class 1 integron markers intI1 and qacE⌬1. PCR analysis with the conserved class 1 integron primers yielded amplicons of approximately 1 kb from E. coli isolates positive for intI1 and qacE⌬1. These PCR amplicons contained the spectinomycin-streptomycin resistance gene aadA1. Further characterization of the identified integrons revealed that many were part of the transposon Tn21, a genetic element that encodes both antibiotic resistance and heavy-metal resistance to mercuric compounds. Fifty percent of the clinical isolates positive for the integron marker gene intI1 as well as for the qacE⌬1 and aadA1 cassettes also contained the mercury reductase gene merA. The correlation between the presence of the merA gene with that of the integrase and antibiotic resistance genes suggests that these integrons are located in Tn21. The presence of these elements among avian E. coli isolates of diverse genetic makeup as well as in Salmonella suggests the mobility of Tn21 among pathogens in humans as well as poultry.

Characterisation of antimicrobial resistance patterns and class 1 integrons among Escherichia coli and Salmonella enterica serovar Choleraesuis strains isolated from humans and swine in Taiwan

“…Frequent resistance patterns of our E. coli and S. Choleraesuis isolates were resistance to ␤-lactams, aminoglycosides, tetracyclines and sulfonamides, in agreement with previous reports from other countries [2,[17][18][19][20][21][22][23][24]. A previous investigation in Taiwan showed that more than 1400 tons of antimicrobial agents were consumed a year for humans and animals.…”

Antimicrobial susceptibilities of Campylobacter isolated from food-producing animals on farms (1999–2001): results from the Japanese Veterinary Antimicrobial Resistance Monitoring Program

“…It is known that resistance to specific antibiotics, such as streptomycin, continues to be prevalent among E. coli isolates despite the discontinuance of use as therapeutic agents [29]. The high frequency of dihydrostreptomycin resistance might have been caused by the widespread use of dihydrostreptomycin and streptomycin.…”

Antimicrobial resistance of Escherichia coli and therapeutic implications

“…Chromosomal and plasmid-borne integrons have been identified as one of the crucial factors for the development of multidrug resistance in Enterobacteriaceae as well as many other bacterial species by harboring and lateral gene transfer of gene cassettes (Bass et al, 1999;Ochman et al, 2000;Roe et al, 2003;Stokes et al, 2001). To date, three distinct classes of resistance integrons have been described with more than 60 different antibiotic resistance genes (Collis et al, 2002;Fluit and Schmitz, 2004;Heir et al, 2004).…”