Investigation of the Correlation between the Presence of Csu Operon Genes and Biofilm Formation in Carbapenem-Resistant Acinetobacter baumannii Isolates in Qom City

Abstract

Background and purpose: Acinetobacter baumannii is an opportunistic pathogen that causes serious infections in hospitalized patients. It is particularly concerning due to its increasing resistance to antibiotics, making it difficult to treat. This bacterium can survive on hospital surfaces for extended periods due to its high resistance to environmental conditions. It can colonize ventilators, form biofilms, and cause pneumonia. A. baumannii with its ability to form biofilm is very important in causing treatment-resistant nosocomial infections. Csu A/BABCDE pilus system, outer membrane proteins, the chrome sensing system, and the pga ABCD operon are virulence factors of Acinetobacter baumanii. Biofilm formation by Acinetobacter baumanii plays a crucial role in the development of hospital-acquired infections. Expression of the CSU operon, which plays a significant role in pilus assembly, the adhesion of bacteria to surfaces, and biofilm formation, is of great importance. This study aimed to investigate the presence of csu operon genes in carbapenem-resistant clinical isolates of A. baumannii and their ability to form biofilms. Materials and methods: A total of 97 carbapenem-resistant clinical isolates of A. baumannii were examined for the presence of csu operon genes (csuA, B, C, D, E, and A/B) using PCR. Isolates were cultured in BHI broth until turbidity reached a McFarland standard of 0.5. 200 μL of each bacterial suspension was transferred into individual wells of a 96-well microtiter plate. The microtiter plate was incubated at 37°C for 24 hours. The biofilm formation assay was conducted using the microtiter plate method. The optical density of the samples was measured at 650 nm using a microplate reader. The biofilm-forming ability of the isolates was compared to that of a negative control (sterile broth) and a positive control (Pseudomonas aeruginosa PA01). The results were analyzed using SPSS software and Pearson's chi-squared test. Results: The results of biochemical and differential tests for 97 carbapenem-resistant Acinetobacter baumanii isolates were summarized. Out of 97 carbapenem-resistant A. baumannii isolates, 62 (63.9%) harbored the csuA gene, 51 (52.6%) harbored the csuB gene, 81 (83.5%) harbored the csuC gene, 29 (29.9%) harbored the csuD gene, 57 (58.8%) harbored the csuE gene, and 54 (55.7%) harbored the csuA/B genes. The presence of the csuC gene was higher compared to other genes, while the presence of the csuD gene was lower. Additionally, 29 isolates (29.9%) exhibited strong biofilm production, 30 (30.9%) exhibited moderate biofilm production, and 38 (39.2%) exhibited weak biofilm production. Conclusion: The results of this study suggest that the csuD gene may play a lesser role in biofilm formation in A. baumannii, as its expression was lower in isolates with strong and moderate biofilm formation compared to other csu operon genes, while the expression pattern of other csu genes in isolates with strong and moderate biofilm formation was relatively similar

Keywords

• acinetobacter
• biofilm
• pcr
• csu operon