General Characteristics and Ecology
The genus Proteus includes four species, of which P. vulgaris and P. mirabilis are of the greatest clinical significance. These microorganisms were first isolated and described by G. Hauser in 1885.
Proteus species are classic opportunistic pathogens. They are part of the normal facultative microbiota of the human vagina and colon. The presence of these bacteria in wastewater is used by sanitation experts as a reliable indicator of environmental fecal contamination.
Microbiologically, they are medium-sized rods (0.4–0.6 by 1–3 µm). In smears, they are arranged predominantly in pairs or form short chains. They do not form capsules, but exhibit high motility due to flagella distributed over the entire cell surface (peritrichous).
Cultural Properties and Dissociation
The bacteria are non-fastidious and grow well on standard nutrient media. A hallmark of the genus is the ability to undergo dissociation, resulting in colonies taking one of two forms:
- H-form (from the German Hauch — film or breath). This is the typical growth pattern accompanied by the "swarming" phenomenon (creeping growth). The bacteria gradually spread across the agar surface, forming characteristic concentric waves or a misty film.
- O-form (from the German Ohne Hauch — without film). This form occurs when microorganisms encounter unfavorable conditions (e.g., the artificial addition of bile salts to the medium). Under these conditions, swarming ceases, and Proteus forms large, isolated colonies with smooth edges.
Biochemical Profile and Resistance
Members of the genus Proteus exhibit extremely high biochemical activity, allowing easy differentiation from other members of the Enterobacteriaceae family.
Key biochemical features of Proteus:
- Production of specific enzymes: phenylalanine deaminase and urease.
- Ability to produce hydrogen sulfide ($H_2S$).
- Ability to liquefy gelatin.
- An important differential negative feature: Proteus species are unable to ferment lactose.
The antigenic structure includes a somatic O-antigen and a flagellar H-antigen. These bacteria are relatively resistant in the external environment, withstanding heating up to 60 °C for one hour and remaining viable in weak solutions of phenol and other disinfectants.
Pathogenesis and Clinical Significance
Infection with Proteus can occur via autoinfection (endogenously) or as a nosocomial (hospital-acquired) infection. The bacterium causes urinary tract infections, wound suppuration, and severe septic conditions.
A key virulence factor in urological infections is the enzyme urease. The mechanism of urolithiasis (stone formation) proceeds in several stages:
- Urease hydrolyzes urea present in the patient's urine.
- This chemical reaction abundantly releases ammonia.
- A sharp alkalinization of the urine occurs (rise in pH).
- In the alkaline environment, the solubility of magnesium and calcium salts drops critically.
- Result: salts precipitate and form kidney stones.
Diagnosis and Treatment Principles
Because protective immunity does not develop after recovery, relapses are possible. Specific prophylaxis (vaccines) is currently unavailable.
Diagnosis relies primarily on the bacteriological method:
- Clinical specimens are inoculated onto lactose-containing differential media (keeping in mind that the bacterium does not ferment lactose).
- Shukevich's method is used: inoculation is performed in the condensation water at the base of a slanted agar slant. This visually captures the characteristic "creeping" growth of Proteus.
- Final identification is achieved by evaluating the biochemical profile of the isolated culture.
Specific coli-proteus bacteriophages are used to treat Proteus infections. Antibiotic therapy must be strictly guided by antimicrobial susceptibility testing results due to the high baseline resistance of the organism.