In this Article, I’m gonna discuss various biochemical reactions for the well known causative agent of Enteric fever, Septicemia & Gastroenteritis i.e. the Salmonella typhi abbreviated as S. typhi.
However, only a few reactions are most commonly used and are medically important for distinguishing pathogenic strains of Salmonella typhi from other non- pathogenic strains as well as from other species of Salmonella which are as follows:
⇒ Produces H2S
⇒ Indole Negative
⇒ Citrate Positive
⇒ Urease Negative
⇒ Methyl red (MR) Positive
⇒ Voges – Proskauer (VP) Negative
⇒ Colorless – NLF colonies on MacConkey agar medium
⇒ Jet black colonies with a metallic sheen on Wilson & Blair bismuth sulfite medium
⇒ Pink or Red Colonies with black center on XLD medium.
Besides that of various biochemical reactions and Sugar fermentation tests, certain enzymatic reactions are also medically important to distinguish Salmonella typhi from other Salmonella sp.
Below is the list of these Enzymatic Reactions and various other biochemical tests for Salmonella typhi which have great importance in research and for knowledge but are not routinely employed:
Catalase +VE (POSITIVE)
Citrate +VE (POSITIVE)
H2S Production +VE (POSITIVE)
Methyl Red +VE (POSITIVE)
Nitrate Reduction +VE (POSITIVE)
Coagulase -VE (NEGATIVE)
ONPG -VE (NEGATIVE)
Esculinase -VE (NEGATIVE)
Indole -VE (NEGATIVE)
Oxidase -VE (NEGATIVE)
Arginine Dehydrolase -VE (NEGATIVE)
Ornithine decarboxylase -VE (NEGATIVE)
Tryptophanase -VE (NEGATIVE)
Urease -VE (NEGATIVE)
VP (Voges Proskauer) -VE (NEGATIVE)
TSI (Triple Sugar Iron Agar) Alkali/Acid
Salmonella typhi ferments various sugars producing acid only as S. typhi is anaerogenic bacteria making it easy to differentiate from other species of Salmonella which ferment sugars producing acid with gas.
But these sugar fermentation tests are of no diagnostic value in routine laboratory tests except Lactose & Sucrose fermentation test, which is of great importance in differentiating Salmonella typhi, which is unable to ferment Lactose and Sucrose, from other Pathogenic & non-pathogenic Salmonella species.
The other sugar fermentation tests which are described below are of great importance in research work.
Galactose +VE (POSITIVE)
Glucose +VE (POSITIVE)
Maltose +VE (POSITIVE)
Mannitol +VE (POSITIVE)
Mannose +VE (POSITIVE)
Melibiose +VE (POSITIVE)
Sorbitol +VE (POSITIVE)
Trehalose +VE (POSITIVE)
Xylose +VE (POSITIVE)
Adonitol -VE (NEGATIVE)
Arabinose -VE (NEGATIVE)
Cellobiose -VE (NEGATIVE)
Lactose -VE (NEGATIVE)
Raffinose -VE (NEGATIVE)
Rhamnose -VE (NEGATIVE)
Salicin -VE (NEGATIVE)
Sucrose -VE (NEGATIVE)
Dulcitol -VE (NEGATIVE)
That’s all about the Biochemical tests for Salmonella typhi.
Identification of Salmonella typhi and paratyphi – Microbeonline