Distribution pattern of carbapenemases and solitary contribution to resistance in clinical strains of Acinetobacter baumannii

Background: This study aimed to investigate the distribution pattern of carbapenemases and evaluate their solitary contribution to carbapenem resistance. Methods: One hundred and twelve isolates of Acinetobacter baumannii (A. baumannii) isolated from the intensive care unit (ICU) of a southern China tertiary hospital were identified, and antimicrobial susceptibility tests (ASTs) of these strains were determined. Common carbapenemases were detected and the distribution pattern of carbapenemases was analyzed. Logistic regression and general linear model analyzed were performed to identify the correlation between antimicrobial susceptibility and carbapenemase genes. Results: These 112 strains were classified into a carbapenem-resistant A. baumannii (CRAB) group (71.7%) and a carbapenem-susceptible A. baumannii (CSAB) group (28.3%). Carbapenemase genes, including bla(OXA-51-like) (100.0%), bla(OXA-23) (93.4%), ISAba1/bla(OXA-51-like) (27.5%), bla(NDM-1) (8.8%), bla(OXA-24) (2.2%) and bla(OXA-58) (2.2%) were detected in CRAB strains, and no bla(SIM), bla(VIM) and bla(IMP) gene in these 112 isolates. There was a statistically significant difference between CSAB and CRAB group in carrying bla(OXA-23) (P<0.001) and ISAba1/bla(OXA-51-like) (P=0.024). Conclusions: A pattern of bla(OXA-51-like) (100.0%), bla(OXA-23) (93.4%), bla(NDM-1) (8.8%), bla(OXA-24) (2.2%) and bla(OXA-58) (2.2%) was detected in CRAB strains. Bla(OXA-23-like) and ISAba1/bla(OXA-51-like) complex might be more relevant to carbapenem resistance in A. baumannii. Harboring bla(OXA-23-like) and ISAba1/bla(OXA-51-like) complex might increase the possibility of resistance 2.16 times [risk ratio (RR): 2.16; 95% confidence interval (CI): 1.04-4.51] and 1.29 times (RR: 1.29; 95% CI: 1.07-1.56), respectively.

Automated summary

This study investigated the distribution pattern of carbapenemases in Acinetobacter baumannii strains isolated from an ICU in southern China. The most common carbapenemases detected in carbapenem-resistant A. baumannii (CRAB) strains were bla(OXA-51-like) and bla(OXA-23). Carrying bla(OXA-23-like) and ISAba1/bla(OXA-51-like) complex may significantly contribute to carbapenem resistance in A. baumannii.