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Abstract
Acinetobacter baumannii is a Gram-negative coccobacillus responsible for severe hospital-acquired infections, particularly in intensive care units (ICUs). The current study was designed to characterize the virulence traits of biofilm-forming carbapenem-resistant A. baumannii causing pneumonia in ICU patients using a Galleria mellonella model. Two hundred and thirty patients with hospital-acquired or ventilator-associated pneumonia were included in our study. Among the total isolates, A. baumannii was the most frequently isolated etiological agent in ICU patients with pneumonia (54/165, 32.7%). All A. baumannii isolates were subjected to antimicrobial susceptibility testing by the Kirby–Bauer disk diffusion method, while the minimum inhibitory concentrations of imipenem and colistin were estimated using the broth microdilution technique. The biofilm formation activity of the isolates was tested using the microtiter plate technique. Biofilm quantification showed that 61.1% (33/54) of the isolates were strong biofilm producers, while 27.7% (15/54) and 11.1% (6/54) showed moderate or weak biofilm production. By studying the prevalence of carbapenemases-encoding genes among isolates, blaOXA-23-like was positive in 88.9% of the isolates (48/54). The BlaNDM gene was found in 27.7% of the isolates (15/54 isolates). BlaOXA-23-like and blaNDM genes coexisted in 25.9% (14/54 isolates). Bap and blaPER-1 genes, the biofilm-associated genes, coexisted in 5.6% (3/54) of the isolates. For in vivo assessment of A. baumannii pathogenicity, a Galleria mellonella survival assay was used. G. mellonella survival was statistically different between moderate and poor biofilm producers (p < 0.0001). The killing effect of the strong biofilm-producing group was significantly higher than that of the moderate and poor biofilm producers (p < 0.0001 for each comparison). These findings highlight the role of biofilm formation as a powerful virulence factor for carbapenem-resistant A. baumannii that causes pneumonia in the ICU.
Highlights
Pneumonia and other lower respiratory tract infections (LRTIs) affect about 10–25%of patients in the intensive care unit (ICU), resulting in approximately 22–71% mortality among these patients [1,2]
Two hundred and thirty (230) patients with hospital-acquired pneumonia (HAP) or ventilator-associated pneumonia (VAP) were included in the study
We investigated the presence of ompA, bap, and blaPER-1 as biofilm encoding genes among carbapenem-resistant A. baumannii (CRAB) isolates from ICU patients with pneumonia
Summary
Pneumonia and other lower respiratory tract infections (LRTIs) affect about 10–25%. Of patients in the intensive care unit (ICU), resulting in approximately 22–71% mortality among these patients [1,2]. Acinetobacter baumannii is a Gram-negative coccobacillus responsible for severe hospital-acquired infections, in the ICU. It causes infections such as bacteremia, pneumonia, urinary tract infection, meningitis, and wound infection [5]. The mortality rate among ICU patients infected by A. baumannii is 45–60%, which may increase to over 80% when extensive drug resistance (XDR) among these pathogens is involved [6]. Insufficient therapeutic options are available for infections caused by multiple drug-resistant (MDR) A. baumannii strains [7,8]
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