Background:Extensive use of cotrimoxazole has been associated with increasing level of Escherichia coli resistance.Objectives:In the current study, we focused on assessing the prevalence of E. coli resistance to cotrimoxazole and frequency of its associated genes.Materials and Methods:One-hundred and forty-four E. coli isolates were identified during March 2007 to April 2012 at Ilam hospitals and Milad (Tehran) hospital. Antibiotic susceptibility for screening of resistance isolates was done by the Kirby-Bauer method. The sul1, sul2, sul3, dfrA1, dfrA5, int1, blaTEM, blaSHV and CTX-M genes were detected by polymerase chain reaction (PCR) amplification. Plasmid curing was done for identifying correlations between resistance genes and plasmids.Results:Amongst the 144 E. coli isolates, seventy-two (50%) Extended Spectrum Beta Lactamase (ESBL)-producing and seventy-two (50%) non-ESBL-producing E. coli isolates were identified; eighty-seven isolates (60.41%) were resistant to cotrimoxazole. Frequencies of sul1, sul2 and sul3, were 81% (116 isolates), 67% (96 isolates) and 2.29% (three isolates), respectively. Furthermore, 50.57% (72 isolates) had sul1 and sul2, 2.29% (3 isolates) contained sul2 and sul3, and 2.29% (three isolates) contained sul1, sul2 and sul3 genes, simultaneously. Thirty-four (39.1%) of the isolates had the dfrA1 gene. Five (5.7%) of the isolates had the dfrA5 gene. Sixty-eight (78.2%) strains contained the int1 gene. Furthermore, dfrA1 and dfrA5 were present in three (3.4%) of the isolates. The results showed that of the ESBL-producing isolates, 85.2% (n = 122), 53.2% (n = 76) and 26.1% (n = 37) were blaTEM, blaSHV and CTX-M harboring isolates, respectively.Conclusions:Our study indicated a high frequency of cotrimoxazole resistance gene in E. coli isolates from Ilam and Tehran (Milad) hospitals, and sul genes had a major role in cotrimoxazole resistance of these isolates.

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Abstract Background Quinolones are broad-spectrum antibiotics, which are used for the treatment of different infectious diseases associated with Enterobacteriaceae. During recent decades, the wide use as well as overuse of quinolones against diverse infections has led to the emergence of quinolone-resistant bacterial strains. Herein, we present the development of quinolone antibiotics, their function and also the different quinolone resistance mechanisms in Enterobacteriaceae by reviewing recent literature. Methods All data were extracted from Google Scholar search engine and PubMed site, using keywords; quinolone resistance, Enterobacteriaceae, plasmid-mediated quinolone resistance, etc. Results and conclusion The acquisition of resistance to quinolones is a complex and multifactorial process. The main resistance mechanisms consist of one or a combination of target-site gene mutations altering the drug-binding affinity of target enzymes. Other mechanisms of quinolone resistance are overexpression of AcrAB-tolC multidrug-resistant efflux pumps and downexpression of porins as well as plasmid-encoded resistance proteins including Qnr protection proteins, aminoglycoside acetyltransferase (AAC(6′)-Ib-cr) and plasmid-encoded active efflux pumps such as OqxAB and QepA. The elucidation of resistance mechanisms will help researchers to explore new drugs against the resistant strains.

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Background: Aminoglycosides are a group of antibiotics that have been widely used in the treatment of life-threatening infections of Gram-negative bacteria. Objectives: This study aimed to evaluate the frequency of aminoglycoside resistance genes in Enterococcus and Salmonella strains isolated from clinical samples by PCR. Materials and Methods: In this study, 140 and 79 isolates of Enterococcus and Salmonella were collected, respectively. After phenotypic biochemical confirmation, 117 and 77 isolates were identified as Enterococcus and Salmonella, respectively. After the biochemical identification of the isolates, antibiotic susceptibility for screening of resistance was done using the Kirby-Bauer method for gentamicin, amikacin, kanamycin, tobramycin and netilmycin. DNA was extracted from resistant strains and the presence of acc (3)-Ia, aac (3′)-Ib, acc (6)-IIa ,16SrRNA methylase genes (armA and rat) was detected by PCR amplification using special primers and positive controls. Results: Enterococcus isolates have the highest prevalence of resistance to both kanamycin and amikacin (68.4%), and Salmonella isolates have the highest prevalence of resistance against kanamycin (6.9%). Ninety-three and 26 isolates of Enterococcus and Salmonella at least were resistant against one of the aminoglycosides, respectively. Moreover, 72.04%, 66.7%, and 36.6% of the resistant strains of Enterococcus had the aac (3′)-Ia, aac (3′)-IIa, and acc (6′)-Ib genes, respectively. None of the Salmonella isolates have the studied aminoglycoside genes. Conclusions: Our results indicate that acetylation genes have an important role in aminoglycoside resistance of the Enterococcus isolates from clinical samples. Moreover, Salmonella strains indicate very low level of aminoglycoside resistance, and aminoglycoside resistance genes were not found in Salmonella isolates. These results indicate that other resistance mechanisms, including efflux pumps have an important role in aminoglycoside resistance of Salmonella.