Virulence Characteristics of Biofilm-Forming Acinetobacter baumannii in Clinical Isolates Using a Galleria mellonella Model

Mahmoud A F Khalil; Fatma A Ahmed; Ahmed F Elkhateeb; Eman E Mahmoud; Mona I Ahmed; Randa I Ahmed; Amal Hosni; Saad Alghamdi; Ahmed Kabrah; Anas S Dablool; Helal F Hetta; Sawsan S Moawad; Enas Mamdouh Hefzy

doi:10.3390/microorganisms9112365

Virulence Characteristics of Biofilm-Forming Acinetobacter baumannii in Clinical Isolates Using a Galleria mellonella Model

Microorganisms. 2021 Nov 16;9(11):2365. doi: 10.3390/microorganisms9112365.

Authors

Affiliations

¹ Department of Microbiology and Immunology, Faculty of Pharmacy, Fayoum University, Fayoum 63514, Egypt.
² Department of Medical Microbiology and Immunology, Faculty of Medicine, Fayoum University, Fayoum 63514, Egypt.
³ Department of Critical Care Medicine, Faculty of Medicine, Fayoum University, Fayoum 63514, Egypt.
⁴ Department of Clinical and Chemical Pathology, Faculty of Medicine, Fayoum University, Fayoum 63514, Egypt.
⁵ Department of Chest Diseases and Tuberculosis, Faculty of Medicine, Fayoum University, Fayoum 63514, Egypt.
⁶ Department of Chest Diseases, Faculty of Medicine, Fayoum University, Fayoum 63514, Egypt.
⁷ Department of Clinical Pathology, Faculty of Medicine, Assiut University, Assiut 71515, Egypt.
⁸ Laboratory Medicine Department, Faculty of Applied Medical Sciences, Umm Al-Qura University, Makkah 24381, Saudi Arabia.
⁹ Department of Public Health, Health Sciences College at Al-Leith, Umm Al-Qura University, Makkah 24381, Saudi Arabia.
¹⁰ Department of Medical Microbiology and Immunology, Faculty of Medicine, Assiut University, Assiut 71515, Egypt.
¹¹ National Research Center (N.R.C), Department of Pests and Plant protection, Giza 12311, Egypt.

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, bla_OXA-23-_like was positive in 88.9% of the isolates (48/54). The Bla_NDM gene was found in 27.7% of the isolates (15/54 isolates). Bla_OXA-23-_like and bla_NDM genes coexisted in 25.9% (14/54 isolates). Bap and bla_PER-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.

Keywords: Acinetobacter baumannii; Galleria mellonella; biofilm; carbapenem; pneumonia.