Clonal relationship and the association of the ST218 strain harboring blaOXA-72 gene to mortality in carbapenem-resistant Acinetobacter baumannii bacteremia

Background/purpose

In 2017, the World Health Organization categorized carbapenem-resistant Acinetobacter baumannii (CRAB) as a priority 1, critical antibiotic-resistant bacteria. This study analyzed the clinical outcomes and investigated the molecular epidemiology of CRAB bacteremia in a medical center in Northern Taiwan.

Methods

We collected 62 blood isolates from patients with CRAB bacteremia from January 2014 to December 2015 at MacKay Memorial Hospital and determined the clonal relationship using the PCR-based technique for molecular epidemiology. Medical charts were reviewed for clinical outcomes.

Results

Fifty-six isolates harbored the bla_OXA-51-like and bla_OXA-23-like carbapenemase genes, 4 isolates harbor the bla_OXA-51-like and bla_OXA-24-like carbapenemase genes and 2 isolates harbored only the bla_OXA-51-like gene. After sequencing, all four isolates of bla_OXA-24-like carbapenemase gene were confirmed to be isolates of bla_OXA-72 carbapenemase genes. In multivariate analysis in the 60 patients, the independent mortality risk factors of CRAB bacteremia included ≥65 years (elderly) (Odds ratio, 4.04, 95% CI, 1.10–14.83, p = 0.035), chronic kidney disease (4.36, 1.14–16.72, p = 0.032). Isolates harboring the bla_OXA-72 gene had the same sequence type (ST218) and PFGE pulsotype raising the possibility of intra-hospital transmission, and all infected patients died.

Conclusion

This study showed the clonal relationship of isolates harboring the carbapenemase gene in CRAB bacteremia. Patients with the ST218 strain harboring bla_OXA-72 gene had high mortality. This warrants further research to determine the mechanism of virulence and risk factors in order to reduce mortality.