Heterogeneous persister cells formation in Acinetobacter baumannii

Area of Science:

• Microbiology
• Antimicrobial Resistance
• Bacterial Pathogenesis

Background:

• Bacterial persistence enables survival against high antibiotic concentrations, a phenomenon observed in various species.
• Acinetobacter baumannii, a significant nosocomial pathogen, lacks comprehensive data on its persistence phenotype.
• Understanding persistence in A. baumannii is crucial for developing effective treatment strategies against this opportunistic pathogen.

Purpose of the Study:

• To investigate and characterize the persistence phenotype in clinical strains of Acinetobacter baumannii.
• To evaluate the variation in persistence among A. baumannii strains following exposure to polymyxin B and tobramycin.
• To explore potential correlations between persistence levels and different antibiotic treatments in A. baumannii.

Main Methods:

• Culturing of 37 polymyxin B-susceptible and 30 tobramycin-susceptible A. baumannii clinical strains.
• Exposure of stationary cultures to specific concentrations of polymyxin B (15 µg/mL) and tobramycin (160 µg/mL).
• Quantification of persister cells using serial dilutions and colony counting post-antibiotic treatment.

Main Results:

• Significant heterogeneity in persister cell formation was observed across A. baumannii isolates.
• Polymyxin B treatment yielded persister cells ranging from 0.0007% to 10.1%, with two isolates showing no detectable persisters.
• Tobramycin treatment also showed high variability (0.0003%-11.84%), with no correlation found between persistence levels for the two antibiotics.

Conclusions:

• This study provides the first evidence of persister cells in Acinetobacter baumannii.
• Distinct regulatory factors likely govern tolerance to unrelated antibiotics in A. baumannii, unlike multi-drug tolerance seen in other species.
• Polymyxin B's limited efficacy against persisters suggests a potential dissociation between persistence and dormancy in A. baumannii.