Staphylococcus aureus (S. aureus) is a major pathogen that causes human pneumonia, leading to significant morbidity and mortality. S. aureus coagulase (Coa) triggers the polymerization of fibrin by activating host prothrombin, which then converts fibrinogen to fibrin and contributes to S. aureus pathogenesis and persistent infection. In our research, we demonstrate that isovitexin, an active traditional Chinese medicine component, can inhibit the coagulase activity of Coa but does not interfere with the growth of S. aureus. Furthermore, we show through thermal shift and fluorescence quenching assays that isovitexin directly binds to Coa. Dynamic simulation and structure-activity relationship analyses suggest that V191 and P268 are key amino acid residues responsible for the binding of isovitexin to Coa. Taken together, these data indicate that isovitexin is a direct Coa inhibitor and a promising candidate for drug development against S. aureus infection.

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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