Prevalence of antibiotic resistance genes in Acinetobacter baumannii isolated from clinical specimens from Pretoria Academic Hospital

Abstract

Acinetobacter baumannii is an important cause of nosocomial infections in hospitals, with most cases occurring in immunocompromised patients. Nosocomial infections are most often associated with medical device related infections due to biofilm formation. These bacteria are difficult to control due to the high resistance in these environments specifically due to their biofilm forming ability. A rise in the number of infections caused by A. baumannii in recent years together with the emergence of pan-drug resistant strains has been noted. An increase in carbapenem resistance worldwide limits the range of therapeutic alternatives in treating Acinetobacter-associated infections. The two main gene families responsible for this resistance are the Metallo-beta-lactamases (MBL’s) and the Carbapenem-hydrolysing-class-D-beta-lactamases (CHDL’s). The MBL genes confer resistance to all beta-lactams, except aztreonam. The CHDL’s are widespread beta-lactamases in A. baumannii and code for carbapenemase activity. These genes can either be plasmid or chromosomally encoded. This study screened for the following MBL genes: IMP, VIM, SIM, SPM and GIM, as well as the following CHDL genes: OXA-23, OXA-24, OXA-51 and OXA-58. The prevalence of these nine antibiotic resistance genes were determined in 97 clinical isolates of A. baumannii using two multiplex polymerase chain reactions (PCR’s). According to the results obtained, OXA-51 had a prevalence of 82% (80/97) and OXA-23 at 59% (57/97). There was only one isolate that was positive for a MBL gene (SPM). A study conducted in Turkey showed prevalence of 78% for OXA-51, which is lower than the 82% prevalence obtained in this study. However, prevalence of 91% was obtained in a study in Singapore for OXA-23, which is higher than the 59% prevalence obtained in this study. A similar study conducted in Brazil on Pseudomanas aeruginosa showed a prevalence of 20-45% for the SPM gene, which is higher than the 1% obtained in this study. According to the results obtained in this study, it is evident that there is an urgent need for further surveillance and monitoring of Acinetobacter baumannii due to the high prevalence of antibiotic resistance genes in this clinical setting.