Effect Of Competition And Synergism Between Gut Bacteria On Aeromonas Hydrophila Infection In Zebrafish

Microorganisms in the intestine play an important role in growth and development,nutritional metabolism and disease defense.Over the past decade,the development of highthroughput sequencing technologies and analysis tools has enabled us to study the microbiota at an exceptional depth and resolution.there is an increasing recognition that many pathogens harbour potent virulence factors in their genomes,yet are commonly associated with asymptomatic carriage.Disease manifestation often depends not only on virulence factors of pathogens,but also on the composition and activity of the cohabiting microbiota.Aeromonas species have been implicated as etiological agents in diseases of fish septicemia,which has caused billions of dollars in economic losses for the Chinese cyprinid fish industry.moreover,the pathogenicity of the Aeromonas is affected by the external environment and by other intestinal microorganisms.In this study,we explore the relationship between Aeromonas invasibility and microbial community structure by antibacterial drugs interference,highthroughput sequencing and network anlaysis.1.Effect of antibacterial drugs on the composition of intestinal flora in zebrafishThe zebrafish gut is mainly composed of Proteobacteria,Firmicutes and Fusobacteria.antibacterial drugs used in this study can significantly change the composition of intestinal flora by increasing the proportion of Proteobacteria and reducing the proportion of Firmicutes and Fusobacteria,in 2,7 days.By 17 days recover from antibacterial drugs treatment,communities composition began to return to their initial state,but the return was often incomplete.Metronidazole treatment group recovers faster than the combined treatment group.2.Efect of antibacterial drugs on the network of intestinal flora in zebrafishAntibacterial drugs can significantly change the network of intestinal flora in zebrafish,increase the number of nodes and links in network compare to control group making the network relationship more compact.At 17 days,there is more competition relationship in the metronidazole treatment network relationship,and there are more synergies relationship in the combined treatment group network.It indicates that the effect of antibacterial agents on the intestinal network is longer than that of the composition of the intestinal flora.3.The relationship between Aeromonas invasibility and microbial community structureAntibacterials can increase zebrafish survival,in the early stage of antibacterial treatment,because of metronidazole treatment can promote the number of potential competition species with Aeromonas(P < 0.05),and the combined treatment can not only increase the number of potential competition with Aeromonas(P < 0.01),but also reduce the number of potential synergistic species with Aeromonas(P < 0.01).At 17 days after treatment,the reason for the low mortality rate in the combined treatment group may be the existence of a large number of potential indirect competition species with Aeromonas in network(P < 0.01).In summary,both the metronidazole treatment group and the combined treatment group can significantly change the intestinal flora composition and network relationship at the initial stage of treatment,but the effect on the intestinal network is more long-term than the influence on the composition of the intestinal flora.It also indicates that the intestinal flora relies on the interaction of the entire network to resist the invasion of pathogens,rather than the interaction between single bacteria.