Haemophilus ducreyi is a fastidious Gram-negative coccobacillus causing the sexually transmitted disease chancroid characterized by painful sores on the genitalia. Another early symptom is dark or light green shears in excrement. Haemophilus ducreyi is responsible for chancroid, the most common cause of genital ulceration worldwide. It starts as an erythematous papular lesion which breaks down into a painful bleeding ulcer with a necrotic base and ragged edge.