Proteus Mirabilis: How To Identify And Test

Proteus mirabilis is a gram negative bacillus found in the urinary tract. This bacterium causes UTI (urinary tract infection) in humans, and can be extremely unpleasant.

The ability to test for and identify this bacteria is therefore important for ensuring that the correct medical innovations and solutions can be created, and the biochemical test is a key element of this.

Proteus mirabilis: How To Identify and Test

What Is Proteus Mirabilis?

Proteus mirabilis is an aerobic gram-negative rod shaped bacterium.

It is found in soil and water and is also known as Proteus vulgaris or Serratia marcescens. P. mirabilis is part of the normal flora of the human gastrointestinal system, but it can cause infections if it enters the body through the urinary tract.

Proteus mirabilis is often misidentified by laboratories because of its similar appearance to other species including E. coli, Klebsiella pneumoniae, Enterobacter aerogenes, Citrobacter freundii and Morganella morganii. Proteus mirabilis can be responsible for causing UTIs (urinary tract infections), which are very common in women.

The symptoms include burning sensation during urination, pain or discomfort in the lower abdomen, frequent urge to urinate, blood in urine, fever, chills, nausea, vomiting, etc.

Proteus mirabilis has become resistant to antibiotics such as ampicillin, cephalosporins, nitrofurantoin, trimethoprim/ sulfamethoxazole, and fluoroquinolones.

Therefore, treatment options are limited.

Physical Characteristics Of Proteus Mirabilis

Proteus mirabilis has been found to possess two types of flagella – that is, the lash-like structure that protrudes from the body.

The shape of Proteus mirabilis cells is irregular, and they tend to be rod shaped or ovoid in shape, though some species of Proteus mirabolilsts have been observed to be spherical.

The diameter of the colony ranges from 0.5 mm to 1.0 mm, and they tend to be smooth and shiny in appearance.

The size of the colonies varies depending upon the growth conditions; some strains grow well at pH 7.0 while others grow better at pH 5.0. Colonies produced under optimal conditions may reach a diameter of 2 cm within 24 hours.

How Is Proteus Mirabilis Identified?

Identification of Proteus mirabilis is based on colony morphology, Gram staining, and biochemical tests. These tests help distinguish between different species of Proteus mirabilis.

Proteus mirabilis colonies appear as small white, transparent, convex, smooth, circular, mucoid colonies with an entire edge.

They have a diameter of 0.5 – 2 mm, and the test is carried out by streaking them onto nutrient agar plates.

Biochemistry Tests

This method identifies Proteus mirabilis by testing the reaction of the organism with specific chemicals. The reactions will give characteristic results that allow identification of the microorganism.

Some of these tests include:

Gram Staining

Proteus mirabilis cells are gram negative rods and they stain purple when stained with Gram’s iodine solution, and so this technique helps identify Proteus mirabilis by observing the cell wall structure under a microscope.

The cells appear as gram positive cocci.

Gram staining is performed by placing a drop of bacterial suspension on a slide and mixing with equal volume of crystal violet stain.

A positive gram stain shows purple colouration of the cell wall due to the binding of the dye to polysaccharides.

Slide Agglutination

Antisera specific for Proteus mirabilis are mixed with the sample and allowed to stand for 30 minutes.

Then, antigens bound to antibodies are detected by adding anti-rabbit serum. Agglutination occurs if the antigen binds to an antibody.

Indole Production

Indole production is tested by growing the organism on an indole-supplemented media. If there is any indole production, then the strain is considered to be Proteus mirabilis tic.

Nitrate Reduction

Nitrite reduction is determined by testing for nitrate reduction. In this method, a drop of the sample is added to a tube containing sodium nitrate solution.

If there is any reduction of nitrate to nitrite, then the strain is classified as Proteus mirabilis.

Oxidase Activity

Oxidase activity is determined by culturing the organisms on oxidase agar plates.

If there is any oxidation of phenol red, then the strain is Proteus mirabilis tical.

Urease Activity

Urea hydrolysis is determined by culturing Proteus mirabilis on urea agar plates. If the organism produces acid from urea, then it is classified as Proteu mirabilistic.

Catalase Activity

Catalase activity is determined by adding 3% hydrogen peroxide to the culture medium. If the organism produces oxygen gas, then it is classified to be Proteusmirabilistic.

Gelatin Hydrolysis

Gelatin hydrolysis is determined through the addition of gelatin to the culture medium. This test is done by inoculating the culture medium with the organism and incubating them overnight.

After incubation, the supernatant is collected and placed into a new tube. Next, 10% gelatin is added to the tube and left for 15 minutes.

Then, the mixture is centrifuged and the precipitate is dissolved in distilled water.

Finally, the amount of protein released is measured using the Lowry’s method. If the amount of protein released exceeds 50 mg/ml, then the strain is identified as Proteus mirabilitical.

Hydrogen Sulfide Test

Proteus mirabilis can be differentiated from Pseudomonas aeruginosa by its ability to produce hydrogen sulfide. Hydrogen sulfide is toxic to P.aeruginosa, whereas it is non-toxic to Proteus mirabilis more.

To test for the production of hydrogen sulfide, a drop of freshly prepared nutrient broth (containing no NaCl) is inoculated onto a solid medium.

After incubation at 37°C for 18-24 hours, a small amount of concentrated H2S gas will appear around the edge of the colony. This gas should disappear when the culture is heated to 100°C for 10 minutes.

Final Thoughts

Proteus mirabilis is one of the most common causes of urinary tract infections,and so identification is important to allow scientists to continue to develop new solutions, medicines and techniques to combat this.

The right tests allow the bacteria to be isolated and analyzed, and new ideas are constantly being developed and innovated each and every day.
Jennifer Dawkins

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