Characteristics of Staphylococcus aureus isolated from lesions of horses.

The research paper is about a study conducted to examine and classify 76 strains of Staphylococcus aureus bacteria from horse lesions. Predominant patterns were found within specific illnesses and antibiotic resistance and toxin production was identified among many of the strains.

Characterizing the Strains

• The researchers began by identifying all 76 strains as either biotypes B or C, and found a nearly even split between the two types.
• They also managed to differentiate 42 of the strains into 7 different coagulase types, a classification that relates to the bacteria’s ability to clot blood plasma.
• They found that Coagulase type V and VII were prevalent in infection of the uterus (metritis) while type II was commonly associated with several other conditions including abscesses (phlegmon), skin inflammation (dermatitis), sinus inflammation (sinusitis), pus in the sinus (empyema sinus) and nasal discharge (nasal catarrh).

Phage Patterns and Antibiotic Resistance

• Besides the coagulase types, the researchers also classified 42 of the strains into 24 different patterns according to how they were attacked by different bacteriophages (viruses that infect bacteria).
• About 60 percent of the strains were resistant to at least one of the six antibiotics tested in the study. Almost all of these strains were resistant to penicillin G, and most of them produced an enzyme known as beta-lactamase, which helps make bacteria resistant to certain antibiotics.

Toxin Production

• Of the 76 strains, only 8 were able to produce enterotoxins, toxins that can cause gastroenteritis, and all of these were from metritis cases.
• Moreover, only one from the phlegmon cases and two from the metritis cases produced other toxins including exfoliative toxin (ET, which causes the skin to peel off) and toxic shock syndrome toxin-1 (TSST-1, which can lead to a sudden drop in blood pressure, fever, and organ damage).
• The latter two were also able to produce enterotoxin C, indicating a more comprehensive virulent characteristic in certain strains.

Significance of the Results

• This research reveals the connection between different strains of S. aureus and the disease conditions they are typically found in, their response to bacteriophages, as well as their level of resistance to particular antibiotics. Such insights are important for deciding treatment strategies for infected horses.
• The study also set a precedence in the scientific community by being the first to show the presence of S. aureus strains in horses that can produce both exfoliative toxin and toxic shock syndrome toxin-1.