Proteus vulgaris

Proteus is a motile, facultative anaerobic, lactose-negative member of Enterobacteriaceae with intensely active flagella that produce the characteristic swarming motility and a distinctive fishy or burnt-chocolate odour on culture. Its urease splits urea into ammonia and carbon dioxide, raising urine pH above 7 and precipitating magnesium ammonium phosphate (struvite) stones, which can grow to fill the renal pelvis as staghorn calculi and act as a nidus harbouring bacteria that cannot be sterilized without stone removal. Other urease-positive organisms worth grouping are Klebsiella, Staphylococcus saprophyticus, Ureaplasma, Helicobacter pylori, and Cryptococcus. Proteus is also the source of the OX antigens used in the obsolete Weil-Felix test for rickettsial disease. Treatment of proteus UTI is usually with trimethoprim-sulfamethoxazole or a fluoroquinolone; P. mirabilis is more common clinically than P. vulgaris and is typically ampicillin-sensitive, whereas P. vulgaris is usually resistant.