Study of the carbapenem resistance mechanisms in clinical isolates of Acinetobacter baumannii: Comparison of burn and non-burn strains

We examined the prevalence of various carbapenem resistance mechanisms in clinical isolates of Acinetobacter baumannii collected from hospitalized burn and non-burn patients. Antimicrobial susceptibility testing was performed for 43 burn and 32 non-burn isolates. Carbapenem resistance genes were identified and repetitive extragenic palindromic PCR (REP-PCR) was used to define clonal relatedness. CarO disruption was investigated by PCR and its expression analyzed by real time reverse transcription-PCR. Of the sixty-four (85%) carbapenem resistant A. baumannii isolates, 42 (66%) and 22 (34%) strains were recovered from burn and non-bum patients, respectively. Isolates were categorized into 6 major REP-PCR patterns; with the highest prevalence of non-bum and burn isolates in pattern A (63%) and B (35%), respectively. Prevalence of bla(OXA-23) was 68% and isolates harbored this element belonged to all REP clusters. The bla(OXA-40-like) was detected in 49% of isolates, with higher prevalence among burn isolates. Three of the four isolates lacked carO gene were cultured from burn patients and level of the carO expression was decreased in carbapenem resistant isolates. These findings show that bla(OXA-23) is widely distributed in carbapenem resistant A. baumannii isolates and other resistance mechanisms such as bla(OXA-40-like) and loss or decreased carO expression could be added in burn strains. (C) 2013 Elsevier Ltd and ISBI. All rights reserved.