Comparison of number of Streptococcus uberis calculated on a volume or weight basis in sand and sawdust bedding

Objective - To determine a method for comparing counts of Streptococcus uberis in sand and sawdust and account for the influence of weight or volume of the bedding material. Sample Population - 2 sources of kiln-dried sawdust and 2 sources of washed sand. Procedures - Sterilized bedding material (100 ml) was weighed and uniformly distributed in an aluminum pan. Each sterilized bedding material was inoculated with a mean of 3.6 × 10⁶ (experiment 1) or 2.4 × 10⁷ (experiment 2) colony-forming units (CFU) of S uberis/ml of bedding material. Without allowing time for replication of S uberis, inoculated bedding materials were washed with sterile saline (0.9% NaCl) solution. A 200-ml aliquot of wash solution was serially diluted up to 2,500 times with additional saline solution and inoculated on plates containing tryptose agar with 5% sheep blood. After incubation for 48 hours, number of CFU of S uberis was counted. This procedure was replicated 19 and 16 times for each bedding material in experiments 1 and 2, respectively. Results - Evaluation of Bonferroni 95% confidence intervals revealed significant differences for counts of S uberis calculated on a weight basis between sand and sawdust. Conclusions and Clinical Relevance - Comparison of counts of S uberis determined on a volume basis for sand and sawdust accentuates to a lesser degree the weight difference of the bedding materials and ensures a more appropriate comparison of number of S uberis.