False-colour transmission electron micrograph (TEM) of Haemophilus ducreyi, the bacterial species causing the sexually-transmitted disease chancroid (a soft sore occurring on mucous membranes of genitals). Individual bacterium are rod-like, Gram- negative, aerobic & non-motile. They grow only in presence of certain factors in the blood (or in presence of certain co-enzymes): they are cultured on fresh blood agar in the laboratory. Chancroid also results in enlargement & ulceration of lymph nodes in groin: treatment is with sulphonamide drugs (septrin) or antibiotics (chloramphenicol). Magnification: X 2,900 at 35mm size.