Bacterial contaminants isolated from lesions of equine histoplasmosis in cart horses of Mekelle town, northern Ethiopia

The aims of the present study were to isolate bacterial contaminants from confirmed lesions of equine histoplasmosis (EH) due to the fungus Histoplasma capsulatum var farciminosum (HCF) in cart horses from the Mekelle town (Northern Ethiopia), to evaluate their antimicrobial resistance and to evidence leukocyte involvement according to the severity of the disease. Bacteriological analyses (germ identification and disc diffusion method drug susceptibility test) were performed on 47 samples (23 closed lesions and 24 open ones) collected from 24 EH positive carthorses with different severity stage of the disease. Six bacterial genuses (Aeromonas, Bacillus, Klebsiella, Staphylococcus, Micrococcus and Rhodococcus) were isolated but Aeromonas and Bacillus were predominantly found in closed lesions whereas Staphylococcus and Bacillus frequently invaded open lesions. Bacillus strains were highly to moderately sensitive to the tested antibiotics (gentamicin, streptomycin, amoxicillin, cefoxitin and tetracycline), the Aeromonas strains were resistant to streptomycin and tetracycline, Staphylococcus strains have developed resistance to all tested antibiotics except for cefoxitin while Micrococcus developed moderate resistance to tetracycline and Rhodococcus strains were poorly responsive to the tested drugs. In addition, significant associations between the severity of the disease and alterations in white blood cell counts (neutrophilia and lymphopenia) were evidenced. These results show that concomitant bacteria infections are frequently observed in equine histoplasmosis, and are involved in the pathogenesis leading to leukocyte recruitment and lymphocyte lysis, requiring an efficient antibiotherapy coupled to antifungal drugs.