The influence of biofilm formation and multidrug resistance on environmental survival of clinical and environmental isolates of Acinetobacter baumannii.

Background: Acinetobacter baumannii is a gram-negative, opportunistic pathogen. Its ability to form biofilm and increasing resistance to antibiotic agents present challenges for infection control. A better understanding of the influence of biofilm formation and antibiotic resistance on environmental persistence of A baumannii in hospital settings is needed for more effective infection control.

Methods: A baumannii strains isolated from patients and the hospital environment were identified via Matrix Assisted Laser Desorption Ionization Time-of-Flight (MALDI-TOF) mass spectrometry (Bruker Daltonics, Bellerica, MA), repetitive extragenic palindromic polymerase chain reaction genotyped, and antibiotic resistance was determined using Vitek 2 (bioMérieux, Inc, Durham NC). Biofilm mass was quantified via microtiter plate method and desiccation tolerance determined up to 56 days.

Results: High biofilm forming, clinical, multidrug-resistant- (MDR) positive strains were 50% less likely to die of desiccation than low biofilm, non-MDR strains. In contrast, environmental, MDR-positive, low biofilm forming strains had a 2.7 times increase in risk of cell death due to desiccation compared with their MDR-negative counterparts. MDR-negative, high biofilm forming environmental strains had a 60% decrease in risk compared with their low biofilm forming counterparts.

Conclusion: The MDR-positive phenotype was deleterious for environmental strains and the high biofilm phenotype was critical for survival. This study provides evidence of the trade-off between antibiotic resistance and desiccation tolerance, driven by condition-dependent adaptation, and establishes rationale for research into the genetic basis of the variation in fitness cost between clinical and environmental isolates.