Proteus Bacteria Characteristics

Study Notes

Proteus bacteria are Gram-negative, aerobic, and highly motile, with a characteristic ammonia smell.
They tend to swarm, spreading rapidly over the surface of solid media, making it difficult to isolate other bacteria.
Adding chloralhydrate or potassium tellurite to the medium can inhibit the spreading of growth.
Proteus does not ferment lactose, rapidly liquefy gelatin, produce H2S, and decompose urea.
On MacConkey agar, colonies appear pale in color, on brilliant green agar and XLD media, red colonies appear.
Colonies are 2-3 mm in diameter, non-hemolytic, shiny, round, and grayish in color.
On KIA, Proteus vulgaris gives A/A + H2S, and Salmonella and P.mirabilis give K/A + H2S.
Proteus species are free-living in water, soil, and sewage, and can cause diseases in the urogenital and gastrointestinal tracts of humans.

Pseudomonas aeruginosa is an important potential pathogen, causing infections in various animal species and humans.
It has been reported to infect wounds, giving rise to blue-green pus, and causing mastitis in dairy cattle, pneumonia in red deer, and green wool infection in sheep.
It is also reported in cases of cystic fibrosis in humans and urinary tract and ear infections.
However, the organism is a frequent contaminant, and its isolation is not necessarily clinically significant.
It is an important hospital-acquired pathogen, causing nosocomial infections.
Pseudomonas aeruginosa grows well on selective agar media used for Enterobacteriaceae, with colony morphology similar to those of enteric bacteria.
However, unlike Enterobacteriaceae, Pseudomonas are oxidase positive.
On blood agar, most Pseudomonas species form large, flat, spreading gray colonies with irregular margins.
Some cultures are mucoid, while others are beta-hemolytic, and most have a fruit-like or sweet ammonia odor.
Pseudomonas aeruginosa is slow-growing at 4°C but grows at 42°C.
It oxidizes glucose but not other sugars, liquefies gelatin, hydrolyzes arginine, and is H2S negative, urea positive, indole negative, oxidase and catalase positive.
In the O-F test, it oxidizes glucose in the aerobic tube, turning the color from green to yellow.