<prompt> An isolate from a wound culture is a Gram-negative rod identified as Bacteroides fragilis. Anaerobic infection with B. fragilis is characterized byA foul-smelling dischargeA black exudate in the woundAn exquisite susceptibility to penicillinA heme-pigmented colony formation  <response>: Bacteroides fragilis is a constituent of normal intestinal flora and readily causes wound infections often mixed with aerobic isolates. These anaerobic, Gram-negative rods are uniformly resistant to aminoglycosides and usually to penicillin as well.Reliable laboratory identification may require multiple analytical techniques. Generally, wound exudates smell bad owing to production of organic acids by such anaerobes as B.fragilis. Black exudates or a black pigment heme in the isolated colony is usually a characteristic of Bacteroides Porphyromonas melaninogenicus, not B.fragilis. Potent neurotoxins are synthesized by the Gram-positive anaerobes such as Clostridium tetani and C. botulinum. 