Molecular and epidemiological characterisation of clinical isolates of carbapenem-resistant Acinetobacter baumannii from public and private sector intensive care units in Karachi, Pakistan

The purpose of this study was to identify molecular and epidemiological characteristics of hospital-acquired carbapenem-resistant Acinetobacter baumannii (CRAB) from two different intensive care unit (ICU) settings in Karachi, Pakistan. A cross-sectional study was performed in the adult ICUs of a private sector tertiary care hospital (PS-ICU) and of a government sector hospital (GS-ICU) between November 2007 and August 2008. Deduplicated CRAB isolates from clinical specimens were examined for carbapenemase and class 1 integrase genes. Isolates were typed using sequence-based multiplex polymerase chain reaction, pulsed-field gel electrophoresis (PFGE) and variable number tandem repeat (VNTR). A total of 50 patients (33 from PS-ICU and 17 from GS-ICU) were recruited. There were statistically significant differences between patients in the two ICUs in terms of mean age, comorbidities, the presence of central venous pressure lines, urinary catheters, and average length of stay. bla_OxA-23-like acquired-oxacillinase genes were found in 47/50 isolates. Class 1 integrase genes were found in 50% (25/50) of the organisms. The majority of isolates belonged to strains of European clones I and II. PFGE typing grouped the isolates into eight distinct clusters, three of which were found in both hospitals. Most of the isolates within each PFGE cluster shared identical or highly similar VNTR profiles, suggesting close epidemiological association. Irrespective of differences in risk factors and infection control policies and practices, the extent of clonality among CRAB isolates was very similar in both ICU settings.