A study of the environmental survival of Streptococcus equi subspecies equi.

This research paper studies the survival of the bacteria Streptococcus equi, which poses a risk to horses worldwide, in various environments during different seasons. The study aims to enhance understanding of how long and vigorously these bacteria can survive outside a host, informing effective disinfection and isolation protocols.

Research Methodology

• The researchers inoculated cultures of Streptococcus equi onto different surfaces that are relevant to equine veterinary practice and stabling. The selection included wood, a shoe sole, cotton overalls, the inside of a nasogastric tube and a dental rasp, a wet plastic bucket, and a fence post.
• They carried out this process in both summer and winter seasons to compare the effects of temperature.
• The inoculated sites were resampled frequently, and bacterial cultures were grown from these samples until no viable bacteria were found.

Evaluating Bacterial Viability

• The viability of the bacteria was measured based on both the duration of survival (time taken until the first negative culture result) as well as the vigour of growth (measured by the growth score over the initial three days of culture).
• The bacterial viability was then compared across the different inoculated sites and seasons.

Research Findings

• It was found that a moist environment and the winter season enhanced the viability of the bacteria.
• The bacteria’s survival duration was relatively short during summer, lasting up to nine days in wet sites and two days in dry locations.
• In contrast, the bacteria thrived longer during winter, surviving up to 34 days in wet conditions and 13 days in dry locations.
• The vigour of bacterial growth in winter was also greater than in summer, as indicated by the three-day growth scores.

Conclusions and Recommendations

• While comparing with the variable size and nature of naturally shed infectious material is challenging, this study suggests that Streptococcus equi can survive in an equine environment longer than previously thought, particularly in wet and cold conditions.
• Therefore, veterinarians and those handling horses should be aware of the potential longevity of these bacteria and tailor their disinfection and isolation strategies accordingly to reduce contagion.