Proteus vulgaris is a species of Gram-negative, rod-shaped bacterium belonging to the family Enterobacteriaceae. It is known for its motility due to peritrichous flagella and its ability to swarm on agar surfaces.
Characteristics of Proteus vulgaris
- Gram-negative rods
- Highly motile, often exhibiting a swarming growth pattern on solid media.
- Oxidase negative.
- Catalase positive.
- Ferments glucose with gas production.
- Produces urease (breaks down urea into ammonia, raising the pH).
- Indole test positive and hydrogen sulfide (H₂S) production.
- Found in soil, water, decaying organic matter, and as part of the normal flora of the human intestine.
- Opportunistic pathogen, often causing urinary tract infections (UTIs), particularly in patients with catheters.
- Associated with wound infections, septicemia, and, less commonly, pneumonia.
- Known for its ability to form struvite stones (kidney stones) due to its production of urease, which alkalizes the urine.
Principle of the Citrate Test
The test detects the ability of the organism to transport and metabolize citrate through the enzyme citrate permease.If the bacterium utilizes citrate, it produces sodium carbonate that raise the pH of the medium.This pH change is detected by the pH indicator bromothymol blue in the medium.
Citrate Test Procedure
- Use Simmons’ citrate agar, which contains citrate, ammonium salts, and bromothymol blue.
- Lightly inoculate the slant surface with the test organism using a sterile loop or needle.
- Incubate at 35–37°C for 24–48 hours.
- After incubation observe the agar.
Proteus vulgaris citrate test result
- Positive : Proteus vulgaris is citrate-positive, meaning it can utilize citrate as its sole carbon source. After incubation, the medium typically turns blue.
- Negative: The medium remains green (neutral pH).