Virulence Profile of Acinetobacter baumannii Isolated from Ventilator-Associated Pneumonia Cases

Abstract

Background: Acinetobacter baumannii (A. baumannii) is an opportunistic bacterium with high antimicrobial resistance and a complex set of virulence factors. It can cause hospital-acquired infections such as ventilator-associated-pneumonia (VAP). The study aimed to detect some virulence factors for A. baumannii isolated from VAP samples phenotypically and genotypically and relating them to antimicrobial resistance. Methodology: Thirty A. baumannii VAP isolates were obtained and tested for antimicrobial sensitivity using the disc-diffusion method. Polystyrene adherence replica method was used to detect bacterial adherence. Capsules were screened using the Anthony capsular staining method. Biofilm forming capacity and serum resistance were also determined. Fifteen genes encoding for either adhesive or non-adhesive virulence factors were detected using multiplex PCR. Results: All A. baumannii isolates showed a high antimicrobial resistance pattern with 60% being multi-drug resistant. Most isolates showed polystyrene adherence; 33.3%, 20% and 26.7% were of high, moderate and low adherence, respectively. All isolates were biofilm formers; 73.3% were moderate or strong biofilm formers. All isolates except 4 were encapsulated and 86.7% showed serum resistance. Most isolates had a high number of virulence genes which correlated significantly with the detected phenotypic virulence factors and multi-drug resistance. Conclusion: A. baumannii VAP isolates could- in a variable degree - adhere to polystyrene, produce biofilm, produce capsule and have serum resistance. Most of these virulence factors were associated with multidrug-resistance and mostly correlated with adhesive and/or non-adhesive virulence genes. A virulence profile was introduced for these isolates that highlights the hazard of this highly resistant and virulent bacterium.