Pathogenesis and Immunity - Proteus

Pathogenesis and Immunity

Proteus organisms are invasive bacteria.

◗ Virulence factors

Proteus possesses following virulence factors:

Pili: Fimbriae or pili are the important virulence factors thatfacilitate adherence of P. mirabilis bacteria to host tissue sites, such as the urinary tract epithelium.

LPS or endotoxin: This causes a series of host inflammatoryresponses and is responsible for Gram-negative endotoxin-induced sepsis caused by Proteus species.

Urease production: The ability ofProteusorganisms toproduce urease is an important factor in pathogenesis of UTI caused byProteus species.

Hydrolysis of urea to ammonia makes the urine alkaline, which provides a suitable environment for Proteus to survive. Subsequently, alkalization of urine leads to precipitation of organic and inorganic compounds, which in turn leads to for-mation of stones in renal calculi. These stones are composed of a combination of magnesium ammonium phosphate (struvite) and calcium carbonate—apatite.

◗ Pathogenesis of UTI

Pathogenesis of Proteus infection depends on the interac-tion between the bacteria and the host defense mechanisms. Adherence of the bacteria to host tissue mediated by fimbriae is the first step in the disease process. The attachment of Proteus species to uroepithelial cells causes secretion of interleukin-6 and interleukin-8. Proteus also induces apoptosis and desqua-mation of epithelial cells. The infection of the urinary tract is facilitated further by production of the enzyme urease and also motility of the bacteria. Urease splits urea into ammonia and carbon dioxide. The ammonia/ammonium buffer pair has a pH of 9.0, leading to excretion of highly alkaline urine, rich in ammonia. The alkalinity of urine contributes to production of renal stones, which is characteristically observed in patients suffering from UTI due to Proteus species.