A malignant pustule is seen in infection with

Cutaneous anthrax: caused by Bacillus anthracis. The lesion stas as a papule 1-3 days after infection and becomes vesicular, containing fluid which may be clear or bloodstained. The whole area is congested and edematous and several satellite lesions filled with serum or yellow fluid are arranged around a central necrotic lesion which is covered by a black eschar. This is a malignant pustule. Reference: Textbook of Microbiology; Anathanarayan and paniker's; 10th edition; Page no: 249