Antibiotic Susceptibility Profile, ESBL Production and blaCTX-M1, blaSHV and blaTEM Types Among Escherichia coli Blood Isolates

Background: Plasmid and chromosomal extended-spectrum beta-lactamases (ESBLs) have been increasingly spread everywhere and blaCTX-M1 is one predominant beta-lactamase. Objectives: This study was fulfilled to determine the production of ESBL and prevalence of blaCTX-M1, blaSHV, and blaTEM among Escherichia coli blood isolates in Tehran. Patients and Methods: Twenty-three isolates were adopted to be studied during 2015-2016. The antibiotic susceptibility testing was performed using Kirby–Bauer method. The combined disk method was used for the detection of phenotypic ESBL production. The most effective antibiotics were piperacillin, amikacin, and ofloxacin. The minimum inhibitory concentration (MIC) of ceftazidime was determined using micro-broth dilution method. Polymerase chain reaction (PCR) was used for detecting the blaCTX-M1, blaSHV, and blaTEM genes. Results: In the broth dilution test, 19 (82%) isolates showed MIC ≥1, and 18 (78.3%) isolates were ceftazidime resistant. In the combined disk test, 19 (82%) isolates were ESBL producers. The results of the MIC and ceftazidime resistance were the same for ESBL selection. The results of MIC, in fact confirmed the disk diffusion in determining the phenotypic ESBL production. The frequency of blaCTX-M1, blaSHV, and blaTEM genes among blood ESBL producing isolates was 26% (n = 6), 8.6% (n = 2), and 0%, respectively. Isolates that showed higher MIC were positive for these genes. Conclusion: The prevalence of multidrug-resistant blood isolates and ESBL phenotype was high in military hospitals. A low number of blood strains amplified blaCTXM1 and blaSHV type beta–lactamases. There was a relationship between the MIC and the presence of beta-lactamase genes.