Emergence of Extensively Drug Resistant Acinetobacter baumannii-Encoding Integrons and Extended-Spectrum Beta-Lactamase Genes Isolated from Ventilator-Associated Pneumonia Patients

Abstract

Background: Acinetobacter baumannii has increasingly become one of the most common pathogens causing ventilator-associated pneumonia (VAP). Objectives: In the present study, we aimed to assess the presence of extended-spectrum beta-lactamase (ESBL) and integron genes in A. baumannii isolates from VAP patients in the intensive care units (ICUs) of 18 hospitals in North of Iran. Methods: All patients, who were ventilated for at least 48 hours, were assessed daily for VAP. The minimum inhibitory concentrations were determined according to the standard protocol by the clinical and laboratory standards institute (CLSI). ESBL-producing A. baumannii was detected, using the double-disk synergy test. ESBL-positive A. baumannii isolates were screened for CTX, VEB, GES, SHV, int1, and int2 genes, using polymerase chain reaction (PCR) amplification. Results: In total, 29 out of 205 patients with nosocomial infections, admitted to ICUs during 2014 - 2015, showed VAP caused by ESBL-producing A. baumannii. A total of 19 (65.51%) strains were extensively drug resistant (XDR). As the findings revealed, the rates of imipenem and colistin resistance were 55.2% and 34.5%, respectively. The prevalence of CTX, VEB, and SHV genes in ESBL-producing A. baumannii was 34.5%, 17.2%, and 96.6%, respectively. Also, 79.3% of the isolates had class 1 integrons, while 10.3% contained class 2 integrons. Conclusions: Presence of integrons in A. baumannii has been considerably associated with ESBL genes. The high rate of SHV and int1 genes highlights the necessity of avoiding aminoglycosides for empirical therapy. Although colistin was the most sensitive antibiotic in XDR strains in our region, due to the presence of patients with A. baumannii in ICUs, colistin resistance screening should be performed before empirical therapy for VAP, even for those without prior exposure to this antibiotic.