A study of the environmental survival of Streptococcus equi subspecies equi

Streptococcus equi represents a common hazard to equids worldwide. Environmental contamination with bacteria shed from an infected horse may represent a significant source of contagion and further knowledge of ex vivo bacterial survival under different conditions is important for disinfection and isolation protocols.

To determine the potential duration of survival and vigour of growth of S. equi inoculated onto surfaces relevant to equine veterinary practice and stabling in summer and winter.

Repeat sampling of environmental inocula of S. equi.

Cultures of S. equi were inoculated onto wood, a shoe sole, cotton overalls, inside a nasogastric tube, inside a dental rasp, in a wet plastic bucket and onto a fence post both in the summer and winter seasons. Frequent resampling and culture from the inoculated sites was conducted until no viable bacteria were found. Bacterial viability was determined by both duration (time to first negative culture) and vigour of growth (growth score over the first 3 days of culture) and compared between inoculated sites and times of year.

Bacterial viability was enhanced by a wet local environment and by the winter season. Survival tended to be short in the summer (up to 9 days in wet sites and up to 2 days in dry sites) but much longer in the winter (up to 34 days in wet sites and up to 13 days in dry sites). Vigour of bacterial growth was also greater in the winter than in the summer as judged by 3-day-growth scores.

Direct comparison with the variable size and nature of naturally shed infectious material is difficult.

Veterinarians and personnel handling horses should be aware that S. equi may survive in an equine environment for longer than previously found, especially when protected by wet and cold conditions.