Proteus Mirabilis vs. Proteus Vulgaris

What's the Difference?

Proteus Mirabilis and Proteus Vulgaris are both species of bacteria belonging to the genus Proteus. However, they differ in certain characteristics. Proteus Mirabilis is known for its swarming motility, which allows it to move rapidly across surfaces. It is commonly found in the human gastrointestinal tract and urinary tract, and can cause urinary tract infections. On the other hand, Proteus Vulgaris is also motile but does not exhibit swarming behavior. It is found in soil, water, and the human gastrointestinal tract, and can cause various infections including wound infections and urinary tract infections. Both bacteria are opportunistic pathogens, meaning they can cause infections in individuals with weakened immune systems or underlying health conditions.


AttributeProteus MirabilisProteus Vulgaris
ClassGamma ProteobacteriaGamma Proteobacteria
Gram StainNegativeNegative
PathogenicityOpportunistic pathogenOpportunistic pathogen

Further Detail


Proteus Mirabilis and Proteus Vulgaris are both species of bacteria belonging to the genus Proteus. They are Gram-negative, facultatively anaerobic, rod-shaped bacteria that are commonly found in the environment, including soil, water, and the intestinal tracts of humans and animals. While they share some similarities, there are also distinct differences between these two species in terms of their characteristics, pathogenicity, and clinical significance.

Morphology and Growth Characteristics

Both Proteus Mirabilis and Proteus Vulgaris are motile bacteria that possess peritrichous flagella, allowing them to move in a characteristic "swarming" pattern on solid media. However, Proteus Mirabilis tends to exhibit a more rapid and extensive swarming behavior compared to Proteus Vulgaris. In terms of colony morphology, Proteus Mirabilis colonies are typically larger, with a characteristic "bull's eye" appearance due to concentric rings of growth. On the other hand, Proteus Vulgaris colonies are usually smaller and do not exhibit the same concentric pattern.

Biochemical Characteristics

When it comes to biochemical characteristics, both Proteus Mirabilis and Proteus Vulgaris are known for their ability to produce urease, an enzyme that hydrolyzes urea into ammonia and carbon dioxide. This urease production can be detected using various laboratory tests, such as the urease test, which involves the addition of urea to a culture medium and observing for a color change due to the production of ammonia. Both species are positive for the urease test, although Proteus Mirabilis tends to exhibit a more rapid and pronounced urease activity compared to Proteus Vulgaris.

Another important biochemical characteristic of Proteus Mirabilis and Proteus Vulgaris is their ability to ferment lactose. While Proteus Mirabilis is non-lactose fermenting, Proteus Vulgaris can ferment lactose, leading to the production of acid and gas. This difference in lactose fermentation can be observed using differential media, such as MacConkey agar, where Proteus Vulgaris colonies appear pink due to the acid production, while Proteus Mirabilis colonies remain colorless.

Pathogenicity and Clinical Significance

Both Proteus Mirabilis and Proteus Vulgaris have the potential to cause infections in humans, particularly in individuals with compromised immune systems or those with indwelling medical devices, such as urinary catheters. However, Proteus Mirabilis is generally considered to be a more common and clinically significant pathogen compared to Proteus Vulgaris.

Proteus Mirabilis is a leading cause of urinary tract infections (UTIs), especially in individuals with urinary catheters. It possesses several virulence factors that contribute to its pathogenicity, including fimbriae, which allow it to adhere to urinary tract epithelial cells, and flagella, which facilitate its motility and colonization. Additionally, Proteus Mirabilis is known for its ability to form crystalline biofilms, which can lead to the formation of urinary stones and recurrent UTIs.

On the other hand, Proteus Vulgaris is less frequently associated with UTIs and is more commonly implicated in other types of infections, such as wound infections, respiratory tract infections, and bacteremia. It also possesses various virulence factors, including fimbriae and flagella, which contribute to its ability to colonize and cause disease.

Antibiotic Susceptibility

Both Proteus Mirabilis and Proteus Vulgaris are known to exhibit intrinsic resistance to certain antibiotics, such as penicillin and ampicillin, due to the production of beta-lactamases. However, their susceptibility to other antibiotics may vary.

Proteus Mirabilis is generally more susceptible to a broader range of antibiotics compared to Proteus Vulgaris. It is often susceptible to drugs such as fluoroquinolones, aminoglycosides, and trimethoprim-sulfamethoxazole. However, the emergence of multidrug-resistant strains of Proteus Mirabilis has been reported, limiting treatment options in some cases.

Proteus Vulgaris, on the other hand, may exhibit a higher level of resistance to certain antibiotics, including fluoroquinolones and aminoglycosides. This resistance pattern may be attributed to the production of various resistance mechanisms, such as efflux pumps and enzymatic inactivation of antibiotics.


In conclusion, Proteus Mirabilis and Proteus Vulgaris are two closely related species of bacteria that share some similarities in terms of their morphology and biochemical characteristics. However, they also exhibit distinct differences, particularly in their growth characteristics, lactose fermentation, pathogenicity, and antibiotic susceptibility. Understanding these attributes is crucial for accurate identification and appropriate management of infections caused by these bacteria.

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