Temperature has a greater effect than salinity on microbial survival in saltwater from a single equine hydrotherapy unit.

Abstract

Objective: To determine the ability of bacteria commonly isolated from equine limb wounds to survive in saltwater obtained from an equine hydrotherapy unit at different salinity concentrations and temperatures.

Methods: Saltwater samples were obtained over a 2-week period (January 22, 2024 to February 2, 2024) from an equine hydrotherapy unit used for clinical patients, kept at either full salinity per manufacturer recommendations or diluted to half salinity to mimic the dilution that likely occurs in the clinical setting between cases when holding tanks are replenished with tap water only. Samples were then autoclaved to eliminate preexisting bacterial contamination before individual inoculation with Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus, and Streptococcus zooepidemicus. Each inoculated sample was maintained at 2, 22, or 44 °C to represent typical holding tank conditions. The bacterial concentration was determined at each condition every 24 hours up to and including 96 hours. The lower limit of detection was set at 1 CFU/mL.

Results: Salinity did not affect bacterial survival. Bacterial concentrations generally decreased with increasing temperature over time. Escherichia coli, S aureus, and S zooepidemicus concentrations decreased to the lower limit of detection at 44 °C by 24 to 48 hours, while P aeruginosa concentrations significantly decreased over 24 hours but remained well above the lower limit of detection.

Conclusions: Common bacterial isolates of equine limb wounds can survive in typical saltwater hydrotherapy conditions.

Clinical relevance: Further investigation is warranted to determine the clinical relevance of these findings including protocols for hydrotherapy unit disinfection, wastage of treatment water, and case inclusion/exclusion criteria.