Antimicrobial resistance of therapeutically problematic Acinetobacter baumannii isolates from Bulgarian university hospitals – chronological trends for the period 2004-2022
Keywords:
Acinetobacter baumannii, therapeutically problematic nosocomial isolates, antimicrobial resistance, chronological trendsAbstract
The present study aimed to explore the antimicrobial resistance (AMR) of therapeutically problematic nosocomial Acinetobacter baumannii isolates from five university hospitals in Bulgaria (2004-2022), as well as to analyze the observed chronological trends. A total of 417 non-duplicate A. baumannii isolates with multidrug resistance (MDR-AB), identified by automated systems, were investigated. The methodology included determination of antimicrobial susceptibility by disk diffusion method, gradient test, and microdilution test, as well as statistical analysis. A chronological AMR increase for all tested antibiotics, except gentamicin, was established from the early (2004-2011) to the late follow-up period (2014-2022). The increase was statistically significant (p < 0.0001), except for tigecycline, and it was highest for imipenem (59.4% resistant (R) isolates in 2004-2011 vs. 93% in 2014-2022), meropenem (58.6%/98.7%), and tobramycin (14.7%/63.5%). In the period 2014-2022, including MDR-AB and extensively drug-resistant A. baumannii (XDR-AB), all with carbapenem resistance (CRAB), the highest in vitro activity was demonstrated by colistin (0% R isolates), ampicillin-sulbactam (34.6% R), and tigecycline (37.5% R). Comparative studies among CRAB isolates in the last decade revealed a significant increase (p < 0.0001) in resistance to two of the most active antibiotics – tobramycin (55.6% in 2014-2016 vs. 86.7% in 2017- 2022) and tigecycline (22.1%/84%), and a reciprocal finding to ampicillin-sulbactam (41.6%/13.3%). There was also a significant increase in the percentage of XDR-AB isolates (from 12.4% to 78.7%, p < 0.0001), which currently represents a serious therapeutic challenge in Bulgarian hospitals. Continuous surveillance of AMR, including newly approved antibiotics, is becoming established as a key element of global and national “One Health” strategies and nosocomial infection stewardship practices.
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