Prevalence of OXA–type carbapenemase genes in carbapenem-resistant Acinetobacter baumannii isolates from patients in intensive care unit at Phramongkutklao Hospital

Abstract

Carbapenem-resistant Acinetobacter baumannii (CRAB) is an important multidrug resistant bacterium. CRAB has been increasingly reported worldwide as a significant causative organism of nosocomial infection, especially for hospitalized patients in intensive care unit (ICU) due to its producing carbapenemase, which mostly consists of oxacillinases for hydrolyzing carbapenem. This study aimed to investigate the prevalence of oxacillinases (OXA)–type carbapenemase genes in CRAB isolates from patients in ICU at Phramongkutklao Hospital from the year 2012 to 2013. Of the 334 isolates, sputum was the most common specimen accounted for 53%. All isolates were detected for carbapenemase production by a modified Hodge test (MHT). All CRAB isolates were MHT-positive. However, these CRAB isolates showed negative results for MBLs detection by EDTA combined disk method and for confirmatory by PCR amplification of MBLs genes (bla_IMP-type, bla_VIM-1-type, and bla_VIM-2-type). Genotyping of OXA–type carbapenemase genes by multiplex PCR revealed 3 OXA-types bla_OXA-23-like, bla_OXA-51-like, and bla_OXA-58-like were detected. Most CRAB isolates harbored more than one type of bla_OXA. From this study, the CRAB isolates were classified into 4 groups: group 1 (harboring both bla_OXA-23-like and bla_OXA-51-like), group 2 (harboring both bla_OXA-51-like and bla_OXA-58-like), group 3 (harboring bla_OXA-23-like, bla_OXA-51-like, and bla_OXA-58-like) and group 4 (harboring only bla_OXA-51-like) with the percentages of isolates 97, 1.2, 0.9 and 0.9 respectively. However, bla_OXA-24-like was not found in any isolated. In conclusion, all CRAB isolated were able to produce oxacillinases by the expression of bla_OXA-23-like, bla_OXA-51-like and bla_OXA-58-like, which is used as main mechanism for carbapenem resistance.