Proteus can cause urinary tract infections and hospital-acquired infections. Proteus is unique, however, because it is highly motile and does not form regular colonies. Instead, Proteus forms what are known as "swarming colonies" when plated on non-inhibitory media. The most important member of this genus is considered to be Proteus mirabilis, a cause of wound and urinary tract infections. Fortunately, most strains of Proteus mirabilis are sensitive to ampicillin and cephalosporins. Unlike its relative, Proteus vulgaris is not sensitive to these antibiotics. However, this organism is isolated less often in the laboratory and usually only targets immunosuppressed individuals. Proteus mirabilis and Proteus vulgaris can be differentiated by an indole test for which only Proteus vulgaris tests positive. Proteus vulgaris occurs naturally in the intestines of humans and a wide variety of animals; also manure, soil and polluted waters.
More than 80% of human urinary tract infections (UTI) are due to the bacterium, Escherichia coli, but urinary infections due to Proteus mirabilis are also well documented. Proteus mirabilis once attached to urinary tract, infects the kidney more commonly than E. coli. Proteus mirabilis belongs to family Enterobacteriaceae and is a gram-negative motile swarmer bacterium. Proteus mirabilis are often found as free living organisms in soil and water but they are also parasitic in the upper urinary tract of human beings.
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