Leishmania major: bacterial contamination of cutaneous lesions in experimental animals

No bacterial contamination has been demonstrated in cutaneous leishmaniasis (CL) nodule and in lesions caused by Leishmania major in Balb/c mice up to 20 days after infection. However, although many phagocytic cells (polymorphonuclear leukocytes and macrophages) were present in the CL lesion, 80% of the lesions showed bacterial contamination that developed within the first 70 days of infection. Topical treatment of the lesion with an ointment containing 15% paromomycin and 12% methylbenzethonium chloride in soft white paraffin for 20 days eliminated all the Leishmania parasites and several of the associated bacteria including: Proteus vulgaris, Pasteurella multocida, Staphylococcus albus and Staphylococcus aureus. This treatment did not affect Escherichia coli, Klebsiella spp. and Pseudomonas aeruginosa. Total elimination of these bacteria was achieved only during the healing process, and within 20 days following termination of treatment. The rate of disappearance of bacteria inoculated alone into the base of the tail of normal uninfected Balb/c mice was much faster than that of bacteria inoculated into either the CL nodule or the CL lesion. This study suggests the development of local immunosuppression in the CL lesion that may be mediated by the Leishmania parasites and their metabolites.