Abstract:

【Objective】 Streptococcus suis type 2 (SS2) is an important zoonotic pathogen. The inosine 5-monophosphate dehydrogenase is a newly found protein of SS2, therefore, the objective of this study is to construct the impdh-knockout strain for further research on the correlation impdh with virulence. 【Method】 The suicide vector pSET4s and chloromycetin (cat) were used to construct the mutant of IMPDH gene by homologous recombination. 【Result】 The results from PCR and Western-blot methods showed that IMPDH gene was successfully replaced. Also, the SS2-H (△IMPDH) was found to be less competent for six carbohydrates metabolism, slower growth curve, far less acidic substances and be less virulent in mouse, rabbit and porcine models of infection than parent SS2. For Balb/c mice, the LD50 of SS2-H (△IMPDH) was 8.3×108 CFU, whereas the LD50 of SS2-H was 3.36×108 CFU. All rabbits infected with SS2-H (△IMPDH) of equal to or above 1.0×109 CFU presented only hyperthermy (i.e. at least 1℃ over the normal body temperature).All pigs infected with SS2-H (△IMPDH) presented only clinical syndromes and could not cause death. 【Conclusion】 The impdh-knockout SS2 was successfully constructed and named SS2-H (△IMPDH). The experiments pathogenicity to swine, Balb/c mice and rabbits indicate that SS2-H (△IMPDH) weakens virulence to sensitive animals.

Key words: Streptococcus suis type 2, IMPDH, gene-knockout strain, virulence