2017 ACVIM Forum Research Abstract Program

To achieve these objectives, MDMs were harvested from 8 apparently healthy, University-owned adult horses. The MDMs of each horse were then separately infected with a macrolide-resistant and a macrolide-susceptible strain of R. equi. Phagocytosis of the bacteria was determined by counting colony forming units (CFUs) from lysed MDMs at baseline (T0 = 45 minutes post-infection). The CFUs were also determined at 48 hours post-infection (T48) with 1 of 4 treatments: no treatment (negative control), PUL-042 alone (PUL), clarithromycin alone (CLR), or a combination of PUL-042 and clarithromycin (PULC). The percentage of CFU reduction was determined by calculating the ratio of CFUs between T48 and T0 for each treatment and multiplying by 100%. Results showed that phagocytosis varied significantly (P < 0.05) among horses. Additionally, there was no significant difference in phagocytosis (i.e., T0 CFU) between strains (P = 0.27). For both macrolide-susceptible and macrolide-resistant R. equi, treatment with CLR or PULC had marked and significant (P < 0.05) reduction of CFU relative to either negative control or treatment with PUL; for both strains, there were no differences between control and PUL or between CLR and PULC. Although the macrolideresistant strain tended to be less effectively reduced, this difference was not significant (P = 0.14).