Identification and MLST analysis of three novel genotypes of Streptococcus equi subsp. zooepidemicus Xinjiang strains

Abstract:

[Background] Streptococcus equi subsp. zooepidemicus (SeZ) not only causes swine Streptococcus disease, but also is an important pathogen that causes strangles. Strangle poses a serious threat to the development of horse and donkey industry in China and it is of great significance to strengthen the molecular epidemiological monitoring of the local SeZ isolates for effective prevention and control of strangle. [Objective] To identify the bacteria and detect drug susceptibility, samples were collected from horse farms in Xinjiang. Molecular epidemic and genetic evolution characteristics of the three endemic isolates were also analyzed. [Methods] Isolation and identification, physiological and biochemical test, drug sensitivity test of 3 isolates (ZHZ113, ZHZ211 and ZHZ523), genetic evolution analysis of 16S rRNA and SeM genes were performed. Seven housekeeping genes (arcC, nrdE, proS, spi, tdk, tpi, yqiL) of 3 isolates were amplified and analyzed through multilocus sequence typing (MLST). [Results] Drug sensitivity results showed that all the three isolates were sensitive to 11 drugs like ceftiofuroxime, cefoxitin, gentamicin, streptomycin, erythromycin, doxycycline, levofloxacin, ciprofloxacin, rifampicin, clindamycin and oxytetracycline. The 16S rRNA gene sequence analysis showed that these three isolates belonged to group II (Streptococcus zooepidemicus). The MLST results showed that 3 sequence types ST39, ST419 and ST421 were found and ST419 and ST421 were identified as novel ST genotypes, which have not been reported. From the analysis of SeM gene sequence and the phylogenetic tree we found that there are variations and dynamic changes in the strangles epidemic distribution from the point of view of different countries, different animals and different time. [Conclusion] This study showed that the 3 isolates were closely related to American canine and horse strains and the results provide valuable information to understand the genotype distribution and molecular epidemic characteristics of SeZ in Xinjiang.

Key words:Streptococcus equi subsp. zooepidemicus;16S rRNA gene;SeM gene;multilocus sequence typing (MLST);microbial susceptibility