Abstract
Integrons are genetic units characterized by the ability to capture and incorporate gene cassettes, thus can contribute to the emergence and transfer of antibiotic resistance. The objectives of this study were: (1) to investigate the presence and distribution of class I and class II integrons and the characteristics of the gene cassettes they carry in Enterobacteriaceae isolated from nosocomial infections at Zagzig University Hospital in Egypt, (2) to determine their impact on resistance, and (3) to identify risk factors for the existence of integrons. Relevant samples and full clinical history were collected from 118 inpatients. Samples were processed; isolated microbes were identified and tested for antibiotic susceptibilities. Integrons were detected by polymerase chain reaction (PCR) and were characterized into class I or II by restriction fragment length polymorphism (RFLP). Integron-positive isolates were subjected to another PCR to detect gene cassette, followed by gene cassette sequencing. Risk factors were analyzed by logistic regression analysis. Seventy-six Enterobacteriaceae isolates were recognized, 41 of them (53.9%) were integron-positive; 39 strains carried class I and 2 strains carried class II integrons. Integrons had gene cassettes encoding different combinations and types of resistance determinants. Interestingly, blaOXA129 gene was found and ereA gene was carried on class I integrons. The same determinants were carried within isolates of the same species as well as isolates of different species. The presence of integrons was significantly associated with multidrug resistance (MDR). No risk factors were associated for integron carriage. We conclude that integrons carrying gene cassettes encoding antibiotic resistance are significantly present among Enterobacteriaceae causing nosocomial infection in our hospital. Risk factors for acquisition remain to be identified.
Highlights
The widespread use of antibiotics with the intra- and interspecies transfer of resistant determinants mediated by plasmids, transposons and gene cassettes in integrons have contributed to the rapid transmission of drug resistance in bacterial pathogens, especially among members of the Enterobacteriaceae family (Cergole-Novella et al, 2011)
Seventy-six Enterobacteriaceae isolates were studied. They were recovered from different clinical samples collected from 118 in-patients admitted to different departments at Zagazig University Hospitals (Table 1)
The highest rate of isolating Enterobacteriaceae was from ICU (42 out of 76)
Summary
The widespread use of antibiotics with the intra- and interspecies transfer of resistant determinants mediated by plasmids, transposons and gene cassettes in integrons have contributed to the rapid transmission of drug resistance in bacterial pathogens, especially among members of the Enterobacteriaceae family (Cergole-Novella et al, 2011). Integrons are mobile DNA elements capable of detention and excision of genes, those responsible for antibiotic resistance. Integrons achieve this by site-specific recombination (Hall and Collis, 1995). There are five different classes of integrons, each encoding a distinct integrase gene (Mazel, 2006). Class II integrons are associated with the Tn7 transposon, whose transposition activity is directed at specific attachment sites on chromosomes or plasmids (RodríguezMinguela et al, 2009). Class I integron possess two conserved segments (5′-CS) and (3′-CS) separated by a variable region including the gene cassettes integrated with antibiotic resistant genes. Class I integron has been identified as the primary source of antimicrobial resistance genes and are suspected to serve as reservoirs and exchange platforms of resistant genes in a variety of Gram-negative bacteria (Ke et al, 2011)
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