<prompt> Most common form of actinomycosisFacio cervicalThorasicRight illiac fossaLiver  <response>: Actinomycosis is caused by Actinomyces israelii. Facio-cervical is the most common type. Infection spreads either from tonsil or from adjacent tooth. Actinomyces israelii is an anaerobic gram - positive fungal like bacterium. It is called as Ray fungus. Reference : SRBs Manual of Surgery, 6th Edition, page no 54. 