Characteristics of an R antigen common to Streptococcus equi and zooepidemicus.

The research involves the study and identification of the R antigen found in the group C streptococcus bacteria strains S. equi and S. zooepidemicus, examining its characteristics, its resistance properties, the presence of different amino acids, its molecular weight, and its possible role in bacterial infections in horses.

Identification and Characteristics of the R Antigen

• The R antigen was identified in both S. equi and S. zooepidemicus bacteria strains.
• The antigen was found to be resistant to acid, heat, and trypsin but sensitive to pepsin. This highlighted its resilience in different conditions, thus posing challenges in its possible control or eradication.
• The antigen was characterized as having an isoelectric point of 4.8, a delicate balance between acid and base where the net charge on the antigen is zero.
• The molecular weight of the antigen was determined to be about 82,000.

Amino Acid Composition of the Antigen

• The amino acids found in the highest concentration in the R antigen are glutamic, aspartic, alanine, leucine, and valine. These amino acids are involved in various functions in living organisms, such as protein synthesis and energy production.

Extraction and Identification of the Antigen

• Large amounts of the R antigen were found to be released using a machine called a French Press.
• The antigen was also found in culture supernatants and acid extracts, highlighting various sources or forms through which it could be isolated.
• Trypsin extraction of the cells yielded molecules of predominately 56,000 and 25,000 molecular weights, appearing similar in their molecular structure to those obtained from trypsinization of purified R protein, derived from the French Press.

Potential Role of the R Antigen

• Horses naturally infected with S. equi or S. zooepidemicus develop cross-reacting R antibodies. However, the role of this antigen in pathogenesis, or the capability to cause disease, remains unestablished.
• R protein does not stimulate bactericidal antibody in horses, nor has it proven protective for mice, indicating its limited potential as a protective antigen or vaccine candidate.
• The presence of the R antigen in antigen preparations for S. equi antibody assays might lead to confusion or errors in interpretation due to the simultaneous presence of antibody to the immunologically similar R antigen of S. zooepidemicus, a bacteria that is commonly present in the nasopharynx of equine species.