Veterynarna biotehnologija – Veterinary biotechnology, 2020, 36, 166-175 [in Ukrainian]. https://doi.org/10.31073/vet_biotech36-17
Institute of Veterinary Medicine NAAS
Bila Tserkva National Agrarian University
THE STUDY OF PECULIARITIES OF SWINE STREPTOCOCCOSIS CAUSATIVE AGENT (S. SUIS) SURFACE ANTIGENES WHEN CULTIVATING IN VITRO
Introduction. Streptococcus suis type 2 is an important pathogen for pig production in almost every country in the world. S. suis causes a range of serious diseases in pigs – arthritis, meningitis, septicemia, pneumonia, leading to significant economic losses in industrial pig breeding. In recent years, there has been a significant increase of streptococcal infections prevalence and its role as an opportunistic factor in the course of viral diseases.
The goal of the work was to study the peculiarities of the antigenic composition of the Streptococcus suis pathogen during cultivation in nutrient media of different composition.
Matherials and methods. It was used strains and isolates of Streptococcus suis, stored and maintained at the Institute of Veterinary Medicine. The bacterial culture was obtained in a BHI medium with pH 7.4-7.6. Different nutrient media variants were obtained by adding defibrinated blood (10%), dry blood plasma (10%) or inactivated bovine serum (10%). Microbial cultures were incubated at 35.5±0.5°C in liquid media for 24-36 hours and in solid media – for 48-72 hours. The protein composition of the obtained antigens was determined by polyacrylamide gel electrophoresis using the classic U.K. Laemmli method (1970). Antigenic activity was studied using the indirect ELISA variant according to the standard protocol using specific sera obtained from white mice.
Results of research and discussion. All tested strains formed a hemolysis zone on blood agar after 24 hours of cultivation. The strains demonstrated the presence of four differentially expressed surface proteins of size 136, 105, 64 and 28 kDa (S. suis strain 3/2) and 136, 64, 42 and 28 kDa (S. suis strain 16/2). The surface proteins of 136 and 64 kDa were expressed in larger amount in the presence of defibrinated blood or blood plasma in the medium. It was found that 105 kDa protein did not produce in significant amount in the medium without blood or serum, which may reduce the virulence of the strains and slightly alter the antigenic properties of pathogenic strains and isolates. The study of weakly virulent S. suis 16/2 strain revealed a significant decrease in the production of surface proteins of 136, 42 and 26 kDa in the blood-free medium variant. As a result of studying the antigenic properties of two strains of swine Streptococcus pathogen showed that highly virulent S. suis strain 3/2 had the highest antigenic activity against both homologous and heterologous sera in ELISA. The antigen of the weakly virulent strain S. suis 16/2 showed a lower antigen affinity for sera obtained for the surface antigens of the pathogenic strain and two pathogenic isolates in ELISA.
Conclusions and prospects for further research. Studies have shown that several S. suis surface proteins were differentially expressed under the influence of the composition of the nutrient medium in vitro. Each variant of the composition of the simulated environment led to changes in the pool of surface proteins. As a result of our studies, we established a relationship between biological properties (virulence level) and antigenic properties in the indirect variant ELISA. The peculiarities of surface antigens composition have the potential to be further investigated for the sensitivity and specificity increasing of diagnostic tests and vaccines.
Keywords: swine streptococcosis, surface antigens, protein composition.