Detection of bla _VIM and bla _IMP metallo-β-lactamase genes by Multiplex PCR among carbapenem resistant Acinetobacter baumannii strains isolated from ventilator associated pneumonia in ICU patients

Abstract

This study was undertaken to examine the microbial causes of ventilator associated pneumonia (VAP) among adult intensive care unit (ICU) patients of Al-ansar Hospital, Medina, KSA and to detect the prevalence of metallo-β-lactamase (MBL) in carbapenem-resistant Acinetobacter baumannii. Microorganisms obtained from different respiratory specimens in patients diagnosed with VAP between January 2011 to January 2014 were included in the current analysis. Standard laboratory methods were used to identify microorganisms, and a standardized susceptibility test was performed. Vitek 2 compact identification system (BioMerieux) using GP-67 and GN-291 cards were also used to confirm the identification. Screening for the detection of MBL in A. baumannii strains was done by disc potention test with EDTA impregnated-impenem and meropenem discs and confirmed by multiplex PCR. A total of 208 clinical isolates of bacteria including Gram negative bacteria constituted 150 (72.1%) of VAP, while Gram positive bacteria constituted 58 (27.9%) of isolates. The most common pathogen associated with VAP was Acinetobacter spp. (26.9%). Patients with primary VAP associated with Acinetobacter spp. were more likely to have nasogastric intubation, sedation and they were on mechanical ventilator for more than 15 days. Out of the 56 strains of A. baumannii isolated form VAP patients, 35 were carbapenem-resistant; of these, 20 were positive for MBL production by potentiated disk test, 17 were positive for bla _VIM by multiplex PCR but none of our strains were positive for bla _IMP. In conclusion, gram-negative pathogens are responsible for most of VAP cases in our patients. A. baumannii is the most common pathogen associated with VAP, especially recurrent cases. Carbapenem resistance in A. baumannii is mainly mediated by MBL production. The common MBL gene is bla _VIM.

Keywords: Recurrent ventilator-associated pneumonia, Acinetobacter baumannii, bla _VIM, bla _IMP, multiplex PCR.