Role of Ibea Gene in Hbmecs Invasion and Biofilm Formation Induced By Neonatal Meningitis Escherichia coli

Background: Bacterial meningitis is a severe infectious disease that affects the central nervous system and can result in high mortality rates and neurological complications. In neonates, meningitis is mainly caused by neonatal meningitis Escherichia coli (NMEC), which invades the intestine, leading to hematogenous spreadand potential bacterial meningitis through blood-brain barrier. Previous studies indicated that the ability of NMEC to adhere and invade is associated with biofilm formation and a deficiency in ibeA may result in decreased virulence and biofilm-forming ability of avian pathogenic Escherichia coli (APEC). Furthermore, the ibeA gene is positioned downstream of ibeR. Our previous studies have shown that ibeR and ibeA genes can both regulate the virulence and relevant phenotypes in E. coli K1. However, the effects of ibeR and ibeA on the biofilm formation and invasion of K1 strain remain to be further studied. Recent studies suggest that indole may act as a signaling molecule to regulate the expression of adhesion and biofilm-promoting factors in E. coli. However, the mechanism by which indole affects biofilms is still unclear. This study aimed to investigate the mechanism of ibeA inhibition of indole-induced NMEC invasion and biofilm formation.

Methods: The viability and growth of the wild strain E44 and ibeA-deletion mutant strain ZD1 were assessed by MTT cell proliferation assay kit (Coolaber). The absorbance values were measured at 490 nm and 540 nm by ELISA. The invasion activities and the biofilm formation ability of E44 and ZD1 were detected in vitro studies. We conducted a cell invasion test using the Human Brain Microvascular Endothelial Cells (HBMEC) model. The ability to form a biofilm was measured at 600 nm using a specific biofilm formation index. Biofilm phenotypic was observed by an confocal laser-scanning microscope(Olympus FV-1000, Japan). Then, we used indole as a regulatory agency to compare its biofilm inhibitory efficacy between E44 and ibeR-deletion mutant strain BR2. The experimental data were analyzed using the SPSS 19.0 statistical package. A statistically significant difference was indicated by P<0.05.

Results: No difference was found in bacterial growth between the E. coli strains E44 and ZD1.

The biofilm formation and HBMECs invasion of ZD1 was significantly lower than that of E44. After treatment with 0.5mM indole, the biofilm formation ability and the ibeA protein expressions of E44 were significantly inhibited. However, indole at different concentrations had no obvious inhibition on BR2 biofilm formation and the ibeA protein expressions.

Conclusion: In summary, the study found that ibeA had a significant regulatory effect on HBMECs invasion and biofilm formation of NMEC, which may inhibit by indole via regulating ibeA through ibeR.

( Acknowledgements: Grant from School of Public Health of Southern Medical University, Guangzhou, China, No. GW202329; J.Z., Q.L. and L.W. contributed equally to this work; Corresponding author: Hong Cao, gzhcao@smu.edu.cn)