This is a case of bubonic plague. Plague is caused by Yersinia pestis. It is sho plump, ovoid, gram negative bacillus, shows bipolar staining (safety pin appearance), pleomorphism which is characteristically enhanced in media containing 3% NaCl. It is enveloped by a slime layer & is non motile, non sporing, non acid fast bacteria. Ref: Ananthanarayanan & Paniker's textbook of microbiology 8th ed pg 322.