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

Morphology of Salmonella Paratyphi

• 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 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 sulphide (H2S) test negative.

Serotyping : With the use of polyvalent and monovalent antisera

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

Pathogenesis

• Ingestion of Salmonella
• Enter into body through lymphoid of pharynx.
• In gut organisms attach with epithelial cells of intestinal villi and penetrate lamina propria, submucosa
• Bacilli phagocytosed by macrophages or polymorphonulcear cells.
• Enter mesesnteric lymph nodes and multiply there.
• Enter thoracic duct and then blood stream.
• It may affect 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

1. Symptoms due to endotoxin
2. step ladder fever
3. Headache
4. Anorexia
5. Congestion of mucus membrane
6. Palpable spleen
7. Rose spots

Further Reading

•  Topley and Wilson’s microbiology and microbial infection – Bacteriology-2-10th Edn.
• Manual of Clinical Microbiology   -Patrick R. Murray -8th Edn.
• Bailey and Scott’s  Diagnostic Microbiology -13th Edn.
•  Mackie & Mc Cartney  Practical Medical Microbiology- 14th  Edn.
• Diagnostic Microbiology -Connie R. Mahon & George Manuselis
• Cowan and Steel’s ,manual for the identification of medical bacteria
• District Laboratory Practice in  Tropical Countries  –  Part-2-   Monica Cheesebrough-   2nd Edn Update