Prevalence of class 1 and class 2 integrons among Escherichia coli isolates of human and animal origin in Lithuania

Abstract

Objectives: Investigation of the prevalence and diversity of class 1 and class 2 integrons in 232 Escherichia coli isolates of human and animal origin obtained during period 2005–2008 in Lithuania. Methods: Total 232 isolates of E. coli from various clinical specimens collected in 5 hospitals in Lithuania (n=98) and from various disease condition and healthy animals (n=134, poultry, swine, cattle) were tested for their antimicrobial susceptibility by disk diffusion method. Isolates resistant to at least two antimicrobials were selected for further studies. PCR and RFLP based analysis were used for the detection of class 1 and class 2 integrons. Resistance gene cassette structure was determined by DNA sequencing of variable parts of integrons. Plasmid location of integrons was confirmed by the conjugation experiments. Results: One hundred out of 232 (43 %) E. coli isolates harboured class 1 and/or class 2 integrons. Class 1/class 2 integrons were detected in 45 E. coli isolates associated with human infections and in 55 E. coli isolates from animal origin.Single class 1 integrons were detected in 78 (34 %) E. coli isolates. Combination of class 1 and class 2 integrons were detected in 4 (2 %) isolates.Eighteen different genes spread within 11 different gene cassette arrays were observed in class 1 integrons. The most frequent cassette arrangements of class 1 integron were as follows ( number of isolates/%): dfrA1+aadA1 (30/37%), dfrA17+aadA5 (22/27%) and aadA1 (11/13%). dfrA1+aadA1, dfrA17+aadA5 and dfrA12+orfF+aadA2 gene cassette arrays were found in isolates either of human or animal origin. aadA1, estX+aadA1, dfrA14+aadA6, aacA4+catB3+dfrA1+orfX, 330bp+sat2+aadA2 gene cassette arrays were exclusively associated with class 1 integrons in isolates from animal origin, whereas dfrA5+ereA2, oxa30+aadA1 and dfrA17+cmlA gene cassette arrays were found in isolates from human origin only. Single clas