Determining the patterns of antimicrobial susceptibility and the distribution of blaCTX-M genes in strains of Acinetobacter Baumannii isolated from clinical samples

Abstract

Background: Nowadays, multidrug resistant (MDR) Acinetobacter baumannii (A. baumannii) strains are as one of the problematic opportunistic pathogens, especially in intensive care units in the world. The purpose of current study was to define the antibiotic susceptibility patterns and detect the prevalence of producing strains of extended-spectrum β-lactamase (ESBL) and the appearance of betalactamase CTX-M-II enzymes in A. baumannii strains. Methods: This study was conducted in 3 major hospitals in Tehran, Iran, on 500 clinical samples during one year. After the identification of isolates in species, test sensitivity was carried out to 4 antibiotics by using the disk diffusion method according to Clinical and Laboratory Standards Institute (CLSI) guidelines; also minimum inhibitory concentrations (MIC) was determined for cefepime, cefotaxime and ceftazidime; and finally, to identify the producing strains of ESBL, phenotypic method of combined-disk was used and then, isolates were considered for presence of blaCTX-M-II gene by polymerase chain reaction (PCR) assay. Findings: 130 Acinetobacter species were isolated from the patients. The majority of isolates was from blood specimens and revealed the highest resistance to cefepime and ceftriaxone. The MIC of cefepime in 91, for ceftazidime in 84, and for cefotaxime in 80 of the studied isolates was more than 128 μg/ml. The results of the combined-disk test demonstrated that 20 of samples were ESBL positive. The PCR results showed that 19 of our isolates had bla CTX-M-II gene. Conclusion: Multidrug resistant (MDR) A. baumannii is widespread in Iran and is considered as hazard risk for hospitalized patients; also by virtue of the results of this survey, there are more significant mechanisms than ESBL bacteria such as secretory pumps and changes in purine resistance which causes more resistance, too, and should be consider