Neisseria gonorrhoeae. Light micrograph of a sample of cells, whose nuclei are small and blue, and three large white blood cells (centre, purple) infected by Neisseria gonorrhoeae bacteria (tiny and round), the agent causing gonorrhoea. Neisseria gonorrhoeae are Gram-negative cocci bacteria with a diameter of about 0.8 micrometers. Gonorrhoea is one of the most common sexually transmitted diseases. It has a short incubation period of two to ten days and it is treated with an antibiotic drug. Treatment for gonorrhoea is effective but does not protect against reinfection. Magnification: x270 at 35mm size.