Salmonella Typhi :Morphology, growth on various media, biochemical tests

Salmonella Typhi: Morphology, Growth on Various Media, Biochemical Tests, Pathogenesis

Salmonella Typhi growth on Various Media and Biochemical Tests

Salmonella Typhi growth on solid media like nutrient agar, blood agar, and MacConkey agar whereas liquid medium, BHI broth and biochemical tests in triple sugar iron (TSI) agar, sulfide indole motility (SIM) test, citrate agar, and urea agar shown above picture.

Morphology of Salmonella Typhi

2 to 3 µm Χ 0.6 µm
Gram-negative bacilli
Motile due to peritrichous flagella
Non- encapsulated
Non-sporing

Colony Characteristics of Salmonella

Aerobic or facultative anaerobes
Optimal temperature 37°C
Optimal pH
Nutrient broth: Uniform turbidity
Blood agar: Colonies 2 to 3 mm, circular, low convex, smooth, translucent, and non-hemolytic
MacConkey agar: Non- lactose fermenter ( colorless colonies)
Deoxycholate Citrate Agar (DCA): Non-lactose fermenter colonies
Wilson and Blair bismuth sulfite medium: Jet black colonies with a sheen
Enrichment media like selenite F broth or tetrathionate broth: Uniform turbidity

Biochemical Reactions

Methyl red positive, Voges-Proskauer test negative, non-lactose fermenter, urea hydrolysis test negative, glucose fermenter, and citrate utilization test variable. Lysine decarboxylase test positive, motile and hydrogen sulfide (H2S) positive.

Serotyping: With the use of polyvalent and monovalent antisera

Kauffmann and White Scheme of serological classification of Salmonella works on the use of these antisera.

Pathogenesis

Ingestion of Salmonella
Enter into the body through the lymphoid of the pharynx.
In the gut, organisms attach with epithelial cells of intestinal villi and penetrate lamina propria, submucosa
Bacilli phagocytosed by macrophages or polymorphonuclear cells.
Enter mesenteric lymph nodes and multiply there.
Enter thoracic duct and then bloodstream.
It may affect the liver, spleen, bone marrow, lung, kidney, and heart.

Special Features of Salmonella

Ability to withstand phagocytosis ( intra-cellular multiplication)
Resistance to bile
Produces endotoxin

Clinical Symptoms

Symptoms due to endotoxin
step ladder fever
Headache
Anorexia
Congestion of mucus membrane
Palpable spleen
Rose spots

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