Streptococcus equi subsp. equi isolated from horses in Southern Brazil: molecular and phenotypic analyses

Area of Science:

• Veterinary Microbiology
• Equine Infectious Diseases
• Bacterial Pathogenesis

Background:

• Strangles, caused by Streptococcus equi subsp. equi (S. equi), is a highly contagious equine disease.
• Clinical signs include lymph node abscessation and respiratory distress, impacting horse health and performance.
• Understanding strain variability is key to managing strangles epidemiology and virulence.

Purpose of the Study:

• To investigate phenotypic and genotypic diversity among S. equi isolates from clinical strangles cases.
• To differentiate circulating S. equi strains by sequencing the seM gene.
• To correlate phenotypic traits with genotypic variations for insights into virulence.

Main Methods:

• Analysis of 23 clinical S. equi isolates from horses with strangles.
• Phenotypic characterization: colony morphology, sugar fermentation, capsule production, biofilm formation, antimicrobial susceptibility.
• Genotypic characterization: sequencing of the 5' end of the seM gene and phylogenetic analysis.

Main Results:

• Identified phenotypic variability in sugar metabolism and capsule expression linked to colony morphology.
• Most isolates showed weak biofilm formation and susceptibility to specific antibiotics, with common tetracycline resistance.
• Sequencing revealed four seM gene alleles (seM-115, seM-158, seM-270, seM-271), with seM-270 and seM-271 being newly identified in the region.

Conclusions:

• Integrated phenotypic and genotypic analyses are essential for understanding S. equi diversity.
• Newly identified seM alleles suggest evolving strains with potential implications for strangles virulence and epidemiology.
• This research provides valuable data for developing targeted control and prevention strategies for strangles.