Characterization of class 1 and class 2 integron gene cassettes in escherichia coil strains isolated from urine cultures: A multicenter study

Abstract

Escherichia coli is the most common pathogen isolated from both nosocomial and community acquired urinary tract infections. Although there are many studies from different centers concerning the antibiotic susceptibility of E.coli isolates in Turkey, the studies are quite few about class 1 and class 2 integron cassettes in clinical E.coli isolates from urinary samples. the aim of the study was to investigate the antibiotic susceptibility and the carriage of integron gene cassettes in E.coli strains isolated from urinary samples. A total of 626 E.coli strains isolated from urine cultures in microbiology laboratories located at 10 provinces from different regions of Turkey (Denizli, Ankara, Kayseri, Nigde, Sanliurfa, Kahramanmaras, Tokat, Malatya, Konya and Trabzon) between June 2011-June 2012 were included in the study. the identification and antibiotic susceptibility testing of the isolates were studied by conventional methods as well as Vitek (R) 2 Compact (bioMerieux, France) and BD Phoenix (TM) 100 (Becton Dickinson, USA) systems. the antibiotic susceptibilities of all the isolates were retested by Kirby-Bauer disk diffusion method according to CLSI recommendations in the main center of the study in order to achive the standardization. the presence of integrons was detected with polymerase chain reaction (PCR) method by using specific primers targeting class 1 (intl1) and class 2 (intl2) integrase gene regions. After integron amplification the samples were cloned and subjected to DNA sequencing. When the antibiotic susceptibility of the isolates were evaluated, the highest resistance was observed against most commonly used empirical antibiotics namely ampicillin and trimethoprim-sulfamethoxazole (SXT) with the mean rate of 58.6% (range: 43.8%-73.2%) and 41.2% (range: 35.4%-45.8%), respectively. the most effective antibiotics detected against the isolates were imipenem and amikacin with the lowest resistance rates of 0.2% (range: 0%-1.1%) and 0.6% (range: 0%-3.2%), respectively. the frequency of positive Intl1 gene and class 1 integron gene cassettes were found as 25.8% (162/626) and 16.6% (104/626), respectively, whereas the frequency of positive intl2 gene II and class 2 integron gene cassettes were 5.1% (32/626) and 3% (19/626), respectively. the lowest intl1 gene frequency was detected in the isolates from Kayseri (16.6%) and the highest in the isolates from Kahramanmaras (35.4%) provinces. While there was no intl2 gene in the isolates from Denizli and Kayseri, the highest frequency was 12.1% in the isolates from Sanliurfa province. dfrA1 gene, the most frequent gene among integron gene cassettes was positive in 31 class 1 integron gene cassette alone, and positive with aadA1 gene in 18 class 1 integron gene cassettes. dfrA1 gene was positive with aadA1 a just in one isolate. dfrA17 allele was positive in one isolate alone, in 28 isolates with aadA1, and in 15 isolates with aadA5. aadA1 gene was detected in four isolates. dfrA17-sat-aadA5 co-existence was detected among class 2 integron gene cassette in isolates from six provinces. dfrA1-sat-aadA1 was detected in one isolate from Ankara province and dfrA1 was detected in one isolate in Nigde province only. As a result, dfrA1 and aadA1 genes are the most common types of genes among class 1 and class 2 integron gene cassettes in E.coli isolated from urine cultures. It was concluded that high resistance against streptomycin (31.2%) and SXT (41.2%) supported the dissemination of integron-mediated genes dfr, sul1 and aad in the isolates.