Which one of the folllowing organisms is not associated with synergistic gangrene

Necrotising fasciitis is a dangerous and rapidly spreading infection of the fascial planes leading to necrosis of the subcutaneous tissues and overlying skin. It is caused by b-haemolytic streptococci and, occasionally, Staphylococcus aureus, but may take the form of a polymicrobial infection associated with other aerobic and anaerobic pathogens, including Bacteroides, Clostridium, Proteus, Pseudomonas and Klebsiella. It is termed Fournier's gangrene when it affects the perineal area, and Meleney's synergistic gangrene when it involves the abdominal wall