Characterization of a mucoid clone of Streptococcus zooepidemicus from an epizootic of equine respiratory disease in New Caledonia.

The research article describes the characterization of a unique strain of Streptococcus zooepidemicus (SzNC), which caused widespread respiratory disease among horses across different parts of New Caledonia.

Objectives of the Study

• The primary goal of the researchers was to investigate a mucoid version of Streptococcus equi subspecies zooepidemicus (Sz), found among New Caledonian horses. They sought to describe its characteristics and how it likely caused an epidemic of respiratory disease among the horses.

Findings of the Study

• Sz is a common bacterium in healthy horses, typically causing no harm. However, this new mucoid strain, named SzNC (ST-307), is noted to cause opportunistic infections in horses dealing with virus infection, extreme temperatures, or stress from transportation or training.
• SzNC was found in 80% of nasal swabs tested from horses affected by the disease. By contrast, only 4% of swabs from unaffected horses yielded colonies of Sz, indicating the strong possible correlation between SzNC and the outbreak of respiratory illness.
• The researchers were also able to exclude the possibility of a viral origin for the disease through culture and antibody screening of early and late serum samples.

Characteristics of the Mucoid Strain

• SzNC displayed a mucoid colony phenotype indicating its sticky or slimy surface. This is often representative of an adaptive switch by some bacteria for survival in harsh environments and, possibly in this case, host invasion.
• Two proteins, DnaK and alanyl-tRNA synthetase (AlaS), were found on the surface of the SzNC isolates but were absent in strains obtained from unaffected horses and unrelated US isolates. These could potentially be involved in the bacterium’s interaction with its host.
• Further analysis of the SzNC protein composition showed a unique structure, which might have contributed to the virulence of the infection.
• A unique feature of the SzNC was its ability to produce hyaluronidase, an enzyme associated with bacterial pathogenicity, implying that it has a greater potential to invade host tissue.

Implications of the Findings

• This study is pivotal for further understanding of Streptococcus equi subspecies zooepidemicus and its potential pathogenicity among horses.
• The findings also provide a significant lead for future studies to develop effective diagnostic tools and treatments for a possible outbreak caused by this bacterium among horses.