Afipia felis is a facultative intracellular bacterium which multiplies in macrophages following inhibition of phagosome-lysosome (P-L) fusion. When A. felis-infected cells are incubated for 72 h with various antibiotics, only aminoglycosides are found to be bactericidal. We therefore studied the killing of intracellular A. felis by amikacin, and its relationship with the restoration of P-L fusion. Amikacin reduced the number of A. felis from 8.5 x 10(5) to 3.5 x 102 cfu/mL within 94 h. P-L fusion was restored after 30-40 h of incubation with amikacin. Both mechanisms may participate in the intracellular killing of bacteria.