Journal of Associated Medical Sciences (Sep 2016)
Phenotypic variation of Streptococcus Suis Serotype 2 isolated from Northern Thai patients characterized by survival in human blood and serum
Abstract
Introduction: Streptococcus suis is one of the most important zoonotic pathogens worldwide. It can cause a wide range of diseases both in pigs and human including meningitis, endocarditis, arthritis and pneumonia. Although several virulence-associated factors have been characterized, specific virulence factors were not clearly defined. Moreover, the genotype of virulence-associated genes involved in virulence of S. suis was uncertain and varied between geographic areas.Objective: To study phenotype of S. suis serotype 2 strains by human whole blood and serum bactericidal assays.Materials and materials: Nine clinical S. suis serotype 2 strains isolated from Northern Thai infected individuals and one isolated from a healthy pig were used in this study. The viability of S. suis strains was determined after incubation in human whole blood or fresh serum. Results: We found that three clinical strains and a pig strain resisted human blood after a four-hour incubation with survival rate ranging from 93-208%. In contrast, growth of the other six clinical strains was inhibited with a survival rate ranging from undetectable to 59%. Surprisingly, we found that five S. suis strains were killed in fresh serum after one hour of exposure with survival rates ranging from 37.12-64.31% and the survival of those strains were restored when incubated with heat-inactivated serum. Additionally, the survival of S. suis in human blood or serum was not associated with their virulence-associated genotypes or symptoms of the patients. Conclusion: Our results suggested that survival of S. suis in human blood and serum was strain dependent. The only three virulence-associated genes (sly, epf, and mrp) could not determine the phenotypic character of S. suis particularly survival in human blood or serum. Since some S. suis strains loss their viability in human serum, further investigation of substances in serum involved in S. suis killing is warranted. Bull Chiang Mai Assoc Med Sci 2016; 49(2): 377-388. Doi: 10.14456/jams.2016.31
