Association of biofilm formation, antimicrobial resistance, clinical characteristics, and clinical outcomes among Acinetobacter baumannii isolates from patients with ventilator-associated pneumonia

Introduction

Biofilm formation is an important virulence factor of Acinetobacter baumannii. Here, we examined the biofilm formation of archived A. baumannii causing ventilator-associated pneumonia (VAP).

Methods

Eighteen and twenty isolates of A. baumannii causing bacteremic pneumonia and non-bacteremic pneumonia were included, respectively. Antimicrobial susceptibility testing was performed by broth microdilution method, while biofilm formation was evaluated by microtiter dish biofilm formation assay.

Results

All 38 isolates were still susceptible to colistin and tigecycline, whereas almost all isolates were non-susceptible (intermediate to resistant) to several antimicrobial agents, especially ceftriaxone and cefotaxime. Approximately, 44% of bacteremic isolates and 50% of non-bacteremic isolates were classified as carbapenem-resistant A. baumannii (CRAB). Biofilm formation was detected in 42% of the studied isolates. Bacteremia among the patients infected with biofilm-producing isolates was significantly higher than in those infected with non-biofilm-producing isolates. The antimicrobial susceptibilities of A. baumannii with biofilm formation were lower than those without biofilm formation, but the differences did not have statistical significance. The patients infected with non-biofilm-producing isolates had good clinical and non-clinical outcomes than those infected with biofilm-producing isolates. The survival rate of patients diagnosed with VAP due to biofilm-producing A. baumannii was lower than in those patients diagnosed with VAP due to non-biofilm-producing isolates.

Conclusion

Biofilm formation of A. baumannii causing VAP was associated with antimicrobial resistance and bacteremia as well as unfavorable clinical outcomes.