Methods of inhibiting phagolysosomal fusion in patients infected with a microorganism involve the administration of a 4-hydroxyphenylpyruvate dioxygenase (HPPD)-inhibiting compound, such as 2-(2-nitro-4-trifluoromethylbenzoyl)-1,3-cyclohexanedione (NTBC) to the patient. A HPPD-inhibiting compound administered in an amount effective to enhance phagolysosomal fusion in the macrophages or neutrophils of the patient reduces or treats the infection. Methods for treating bacterial infections by administering a HPPD-inhibiting compound and reducing the production of pyomelanin or melanin in microorganisms are disclosed.