Abstract：Haemophilus parasuis (HPS) is the pathogen causing Glasser's disease, which is one of the most serious bacterial pathogens that harm the health of pigs clinically. There are many serotypes of HPS, serotype 4 is the most isolated serotype and the more serious serotype. crp gene encodes cAMP receptor protein (crp) and crp is one of the most important systemic regulatory factors and plays a crucial role in adapting to environmental changes during bacterial infection. In order to study the effect of crp gene on biological characteristics of HPS type 4 (HPS4) such as growth, resistance and virulence, the crp gene deletion strain Δcrp of HPS type 4 clinical isolate HPS4 was constructed by natural transformation method. Morphological characteristics, growth characteristics, biofilm formation, tolerance pressure, serum bactericidal activity, iron utilization and mice (Mus musculus) infection assays of HPS4 and Δcrp were studied. The results showed that crp deletion strain Δcrp of clinical isolate of HPS4 was successfully constructed in this study. After crp was deleted in HPS4, the growth was significantly slowed down, the biofilm formation ability was significantly weakened, the tolerance to osmotic pressure, oxidative stress and heat stress was decreased, the serum survival ability was decreased, the iron utilization was decreased and the virulence of mice was decreased. The results indicated that crp gene had significant effects on growth, resistance and virulence of HPS4. This study provides basic data for further exploring the function of crp gene and screening attenuated strains of HPS4.
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