Fig. 1.

N. gonorrhoeae (Ngo) is able to survive and replicate in association with HL-60 cells. (A) Differentiated HL-60 cells were infected with piliated strain FA1090 at an MOI of 1. Viable CFU/ml were enumerated at various times postinfection, and the data are represented as the means ± SD for 3 independent replicates and are representative of 3 independent experiments. The growth of bacteria in infection medium alone was also determined. (B) N. gonorrhoeae bacteria associated with HL-60 cells are both intracellular and extracellular. Differentiated HL-60 cells were infected at an MOI of 24 for 1 h, after which the cells were fixed and intracellular and extracellular bacteria were differentiated based on accessibility of an N. gonorrhoeae-specific antibody before and after cellular permeabilization. Extracellular bacteria appear red and yellow, and intracellular bacteria appear green.