Introduction: The aim of the experiment was to establish the enterotoxigenic Escherichia coli K88 (ETEC K88)-induced BALB/c mouse duodenum inflammation model. Material and Methods: Mice were administered different concentrations of E. coli K88 (1.0 × 10 7 -10 9 CFU/mL) for 3 d by means of an esophageal catheter. Results: The results showed that the treated group expressed several significant clinical symptoms, such as reduced dietary demands and weight loss, an increased presence of IL-1α, TNF-α, and MPO in the peripheral blood, and some pathological changes in the duodenum. On the 6 th -8 th days, the body weight of the mice was the lowest. On the 8 th day, there were significant differences in IL-1α, TNF-α, and MPO levels compared to the control group (P < 0.05), the gap between the duodenum mucous layer and the muscular layer had widened, the number of goblet cells was increased, and the inflammatory infiltrate and inflammation changes in the lamina propria and the mucous layer were the most obvious. Conclusion: The duodenum inflammation was the most severe on day 8; thus, the model was successfully established. In addition, varying concentrations of ETEC K88 did not significantly influence the duodenum inflammation (P > 0.05).

Pasteurella multocida (Pm) is one of the major pathogens of bovine respiratory disease (BRD), which can develop drug resistance to many of the commonly used antibiotics. Our earlier research group found that with clinical use of enrofloxacin, Pm was more likely to develop drug resistance to enrofloxacin. In order to better understand the resistance mechanism of Pm to enrofloxacin, we isolated PmS and PmR strains with the same PFGE typing in vitro, and artificially induced PmR to obtain the highly resistant phenotype, PmHR. Then transcriptome sequencing of clinically isolated sensitive strains, resistant and highly drug-resistant strains, treated with enrofloxacin at sub-inhibitory concentrations, were performed. The satP gene, of which the expression changed significantly with the increase in drug resistance, was screened. In order to further confirm the function of this gene, we constructed a satP deletion (ΔPm) strain using suicide vector plasmid pRE112, and constructed the C-Pm strain using pBBR1-MCS, and further analyzed the function of the satP gene. Through a continuously induced resistance test, it was found that the resistance rate of ΔPm was obviously lower than that of Pm in vitro. MDK99, agar diffusion and mutation frequency experiments showed significantly lower tolerance of ΔPm than the wild-type strains. The pathogenicity of ΔPm and Pm was measured by an acute pathogenicity test in mice, and it was found that the pathogenicity of ΔPm was reduced by about 400 times. Therefore, this study found that the satP gene was related to the tolerance and pathogenicity of Pm, and may be used as a target of enrofloxacin synergistic effect.

Pasteurella multocida capsular type A (PmA) is one of the main pathogens causing bovine respiratory disease in China. The prevention and control measures against Pm are traditionally based on the use of broad-spectrum antibiotics. Previous studies found that Pm was prone to antibiotic resistance and tolerance mutation under the action of low concentrations of antibiotics, ultimately causing difficulties in prevention and control against Pm. In this study, highly pathogenic Pm fluoroquinolone-sensitive strain P3 and fluoroquinolone-resistant strain P32 induced by sub-inhibitory concentration of enrofloxacin were selected as research objects. RNA-seq was used to screen the differential gene recO of SOS response of P3 and P32 for functional verification. In addition, through MIC, MBC, induced resistance time, time-kill curve analysis and antibiotic tolerance test, the effect of recO gene on the resistance and tolerance of Pm to fluoroquinolone was clarified. At the same time, using fluorescent reporter vector, it was found that recO gene affected SOS repair response. In conclusion, the inhibition of recO gene can not only reduce their resistance to fluoroquinolone, but also prolong the formation time of fluoroquinolone resistance. It is speculated that recO gene is a potential target of fluoroquinolone synergistic antibacterial agent.

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