PROTEUS, PROVIDENCIA, AND MORGANELLA
Proteus, Morganella, and Providencia are also opportunistic pathogens found with vary-ing frequencies in the normal intestinal flora. Proteus mirabilis, the most commonly iso-lated member of the group, is one of the most susceptible of the Enterobacteriaceae to the penicillins; this characteristic includes moderate susceptibility to penicillin G. Other Pro-teeae are regularly resistant to ampicillin and the cephalosporins. Proteus mirabilis and Proteus vulgaris share the ability to swarm over the surface of media, rather than remain-ing confined to discrete colonies. This characteristic makes them readily recognizable in the laboratory — often with dismay, because the spreading growth covers other organisms in the culture and thus delays their isolation. Proteus and Morganella differ from other Enterobacteriaceae in the production of a very potent urease, which aids their rapid iden-tification. It also leads to production of urinary stones and produces alkalinity and an am-moniac odor to the urine. Providencia species do not produce urease, are the least fre-quently isolated, and are generally the most resistant of the group to antimicrobics.