This photograph depicts the colonies of Proteus mirabilis bacteria grown on a Xylose Lysine Sodium Deoxycholate (XLD) agar plate.P. mirabilis is a Gram-negative bacterium from the family Enterobacteriaceae, and is part of the normal flora of human gastrointestinal tract. However, if this bacterium enters the urinary tract, wounds or lungs it can become pathogenic. Xylose Lyseine (XL) agar is used when trying to culture and isolate Gram-negative enteric bacilli, i.e., rods. When XL agar is supplemented with sodium thiosulfate, ferric ammonium citrate, and sodium deoxycholate, it is then termed XLD agar, and is then an even more selective medium than XL alone. The presence of any black color indicates the deposition of hydrogen sulfide, (H2S) under alkaline conditions.
Proteus Infection
Proteus species are most commonly found in the human intestinal tract as part of normal human intestinal flora, along with Escherichia coli and Klebsiella species, of which E. coli is the predominant resident.
Proteus is also found in multiple environmental habitats, including long-term care facilities and hospitals. In hospital settings, it is not unusual for gram-negative bacilli to colonize both the skin and oral mucosa of both patients and hospital personnel.
Infection primarily occurs from these reservoirs. However, Proteus species are not the most common cause of nosocomial infections.
Proteus mirabilis causes 90% of Proteus infections and can be considered a community-acquired infection.
Proteus vulgaris and Proteus penneri are easily isolated from individuals in long-term care facilities and hospitals and from patients with underlying diseases or compromised immune systems
Proteus can cause urinary tract infections and hospital-acquired infections. 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. is unique, however, because it is highly motile and does not form regular colonies.
Instead,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.
