The Regulatory Role Of The QS System In The Host Cell Inflammatory Response Induced By Acinetobacter Baumannii And Its Effect On Zebrafish Infection Model

Acinetobacter baumannii(Ab)is currently one of the most important conditional pathogens worldwide,and its strong ability to acquire drug resistance has made clinical anti-infection treatment more difficult than ever.The Quorum sensing(QS)system is an important signal sensing system widely found in bacterial populations.Bacteria regulate their own population behavior by sensing population density,thus regulating the various biological functions involved,such as biofilm formation and virulence factor production,in order to better adapt to their environment.Recent studies have revealed that the QS system not only regulates the population behavior of microorganisms themselves,but also directly affects the physiology,metabolic regulation and immune function of eukaryotic host cells,regulating host immune responses and inducing host cell damage through interspecies signaling.Currently,it is not clear about the interactive regulation of the QS system of Acinetobacter baumannii on bacteria and hosts.Based on the above background,In this study,the wild strain of A.baumannii and the mutant strain Δaba I,which encodes the deletion gene of the QS signaling molecule,were used to investigate the effects of the QS system on the biological functions of the bacteria themselves and their infection of human lung epithelial cells,respectively,and to study the effects of the QS system on the dissemination and pathogenicity of the bacteria in zebrafish through a zebrafish infection model.Further,to reveal the biological effects of the QS system in the host cell inflammatory response induced by Acinetobacter baumannii.This is important for us to apply the QS system to regulate the interaction between A.baumannii and the host for effective control of A.baumannii infection.Methods and Results:(1)Effect of QS system on the biological function of A.baumannii itself.In this study,the bacterial growth curve,biofilm formation ability,surface motility and adhesion and invasion ability to A549 were determined using WT,Δaba I and Δaba I+AHL of A.baumannii,respectively.The results showed that: Δaba I showed significantly slower growth,weaker biofilm formation ability,motility,and adhesion and invasion ability to A549 than the WT;while Δaba I+AHL showed similar changes to the WT.(2)Effect of QS system on A.baumannii induced A549 damage and inflammatory response.We examined the cell viability,cell morphology and production of inflammation-related cytokines after WT,Δaba I and Δaba I+AHL infection of A549,respectively.The results showed that the deletion mutation of QS system significantly decreased the production of inflammatory cytokines induced by Ab as well as the remodeling of cell structure,significantly decreased cell viability,and ultimately induced an immune response in A549.Subsequently,by RNA-Seq analysis,we found that the QS system stimulated the inflammatory response in A549 induced by A.baumannii through the MAPK signaling pathway.(3)Effect of QS system on zebrafish model of Ab infection.We used WT,Δaba I,and Δaba I+AHL,imbibed with a juvenile zebrafish model at 72 hpf to investigate the effect of the QS system on the pathogenicity and intrinsic immune response of A.baumannii.We examined the LD50 of the three strains of A.baumannii on zebrafish,zebrafish morphology,bacterial dispersal in zebrafish and production of inflammatory cytokines in zebrafish,respectively.The results showed that QS significantly reduced the LD50 of A.baumannii on zebrafish;zebrafish showed symptoms of tail curl,decreased coordination when swimming,and mortality after infection with the wild strain,whileΔaba I showed slight tail curl and no mortality compared with WT,indicating that QS significantly affected A.baumannii pathogenicity;In addition,the Δaba I reproduced and spread more slowly compared to WT,and the production of inflammatory cytokines was significantly lower in Δaba I-infected zebrafish.Conclusions:(1)The QS system of A.baumannii is closely related to the ability of bacterial biofilm formation,surface motility and adhesion to and invasion of A549(2)The aba I gene deletion mutation reduces bacterial damage to infected cells and its induced inflammatory response in A549,and QS may regulate the host cell inflammatory response by activating the MAPK signaling pathway.(3)The aba I gene deletion mutations reduce the inflammatory response induced by bacterial infection and pathogenicity to zebrafish.