Biochemical tests for Salmonella typhi (S. typhi) | Bacteriology Notes

BIOCHEMICAL TESTS FOR SALMONELLA TYPHI (S. TYPHI)

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

salmonella typhi on Macconkey agar medium - salmonella on macconkey agar medium
SALMONELLA TYPHI 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.

Salmonella typhi on xld medium - salmonella typhi on Xylose lysine deoxycholate agar medium
SALMONELLA TYPHI ON XLD MEDIUM

Check out the Morphology & Culture Characteristics of Salmonella typhi

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:

TESTSRESULTS
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.

Check out the Biochemical tests for Klebsiella pneumoniae

https://paramedicsworld.com/klebsiella-pneumoniae/biochemical-tests-for-klebsiella-pneumoniae-k-pneumoniae/medical-paramedical-studynotes

The other sugar fermentation tests which are described below are of great importance in research work.

SUGARSRESULTS
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.



Further Reading:

Identification of Salmonella typhi and paratyphi Microbeonline

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