Novel Genotype of Streptococcus dysgalactiae subsp. equisimilis Associated with Mastitis in an Arabian Filly: Genomic Approaches and Phenotypic Properties.

The researchers identified a new genotype of the bacterium Streptococcus dysgalactiae subsp. equisimilis (Sde) associated with equine neonatal mastitis, a condition causing inflammation in the mammary gland in horses. Using genomic analysis, antibiotic susceptibility tests, and virulence factor assays, they identified unique properties of this strain.

Genomic Analysis & Identification

• Sde was isolated from an 8 day-old filly (a young female horse) and sequenced for genome analysis. This process involves reading the arrangement of DNA sequences to determine the genetic makeup of the organism.
• The Sde strain analysed presented the novel emm-subtype stC839.12 and multilocus sequence type ST-670. Both these features are unique and have not been seen in Sde before, marking this as a novel genotype. Multilocus sequence typing is a technique used to distinguish strains of microorganisms.
• This genotype was found to belong to a specific equine genotype group, indicating that it is particularly associated with horses.

Antibiotic Resistance

• While the researchers did not find any specific genotypic mechanisms related to antibiotic resistance, the Sde strain did possess genes encoding efflux pumps and transporters (pmrA, bmrC, and lmrP). These are systems that bacteria use to remove toxins, including some antibiotics, from their cells.

Virulence Factors

• The researchers identified genes responsible for several virulence factors (VF). VFs are molecules produced by bacteria that increase their ability to establish infection.
• These included emm, cpa, fbp-2, adcA, hyl, htrA, tig, slo, and ndk. Each of these genes contributes to the Sde bacteria’s ability to infect and cause disease in the host.
• They also found loci encoding phosphoenolpyruvate-protein phosphotransferase systems, which are used by bacteria to import and metabolise sugars.

Significance of the Study

• This is the first report of an equine neonatal mastitis case caused by a novel genotype of Sde. The findings will contribute to a better understanding of the genetic diversity of Sde and may facilitate the development of improved diagnostic measures and treatments for equine mastitis.