Comparison of the bacterial and fungal flora in the pharynx of normal horses and horses affected with pharyngitis.

A total of 43 horses were used for the study of the pharyngeal bacterial flora. The median value of the number of bacteria in the group of 19 normal horses was 3.8 x 10(4) cfu/g of secretions. This value was 6.4 x 10(4)cfu/g in horses with grade I pharyngitis, 1.3 x 10(5) cfu/g in horses with grade II pharyngitis and 3.5 x 10(6) cfu/g in horses affected with grades III and IV pharyngitis. Corynebacterium spp, coagulase-negative staphylococci, Nocardia spp, Moraxella spp and Enterobacter spp were the most frequently encountered bacteria in the normal animals as well as in horses affected with pharyngitis of grades I or II. Moraxella spp were isolated in 87.5% of the horses with pharyngitis of grades III and IV, followed by Streptococcus zooepidemicus, Pseudomonas aeruginosa, coagulase-negative staphylococci and Enterobacter spp. No fastidious bacteria, nor strict anaerobes were isolated from any of the 43 horses. None of the microorganisms were found in 100% of the animals and the majority of the isolates were opportunistic bacteria. These results demonstrate that the isolation of Moraxella spp and S. zooepidemicus in large numbers is frequent in horses with lymphoid follicular hyperplasia grades III and IV. Fungi were isolated in small numbers from two or three horses in each group.