Laboratory diagnosis of typhoid

Laboratory diagnosis of typhoid:

For laboratory diagnosis of typhoid, efforts are made to:

(1) Isolate and recognize the organism

(2) To identify a particular immunological response to the agent or

(3) Directly notice the etiological agent, or its particular products antigens or genomic elements-possibly subsequent to amplification.

Isolation of the etiological agent
:

Selective and indicator media:

Indicator and selective media are necessary to permit the isolation of enteric pathogens from contaminated sites. In most of the media, selection was acquired by the incorporation of certain dyes. Lactose non fermentation was the foundation of indication of probable colonies. More than a single medium, Leifson’s deoxycholate-citrate agar (i.e., DCA), Taylor’s xylose-lysine-deoxycholate (i.e., XLD) and variants of Wilson and Blair’s bismuth sulphite media are all extremely effective.

Enrichment media:

For culture from faeces and another contaminated specimen, primary particular enrichment of the pathogen in a liquid medium was employed that raised the yield. Muller’s tetrathionate broth and selenite broths of Leifson, are usually employed. More than a single broth is necessary to recover a full variety of serovars of Salmonella.

Selection of specimens:

S.typhi is maximally isolated from blood in the primary week of disease, from faeces in the second and subsequent weeks, and from urine in the third and fourth weeks.

Blood:

Blood culture is the most helpful diagnostic process for the diagnosis of clinical enteric fever. It is frequently positive during the early ambulant stage of the disease. It persists to be positive until efficient treatment is provided. It is positive during relapses.

For accomplishment, 10 ml of blood is taken into an appropriate 50 ml of liquid medium on numerous occasions. ‘Clot culture’ in which the serum is eliminated from a blood specimen and the clot is employed for culture.

Faeces:

Culture of faeces is a standard diagnostic method and recurring specimens over 2-3 days must be tested as there is variation in the shedding of organisms.

Urine:

During enteric fever, organisms are frequently shed in the urine, and for diagnosis of cases or carriers 5-20 ml volumes can be mix with equivalent volumes of selenite enrichment broth for incubation and subculture.

Bile:

Culture of a duodenal aspirate, enrich in bile, has yielded S. typhi whenever other techniques have failed. Both cases and carriers have been diagnosed.

 

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