typhoid-toxin

An estimated 26 million cases of typhoid fever and 5 million cases of paratyphoid fever occur worldwide each year, causing 215,000 deaths. Incidence also varies by season with yearly peaks coinciding with the monsoon. Investigations into this and other outbreaks have found that they are point-source epidemics caused by Salmonella typhi and Paratyphi A, Paratyphi B (tartrate negative), and Paratyphi C cause a potentially severe and occasionally life-threatening bacteraemia illness referred to respectively as Typhoid and Paratyphoid Fever, and collectively as Enteric Fever.
Salmonella bacteria are classified as either “Typhoidal” or “Non- Typhoidal,” based on their serotype.

TRANSMISSION

Salmonella typhi is spread through the faecal-oral route from individuals that are currently infected and from asymptomatic carriers of the bacteria. Unlike other strains of Salmonella, there are no animal or environmental reservoirs have been identified. Humans are the only source of these bacteria. Few instances which can lead to the cause:

  • 1- Using a toilet contaminated with bacteria and touching your mouth before washing your hands
  • 2- Eating seafood from a water source contaminated by infected faeces or urine
  • 3- Eating raw vegetables that have been fertilised with human waste
  • 4- Contaminated milk products
  • 5- Having oral or anal sex with a person who's a carrier of Salmonella typhi bacteria.

About 3% of infected people (treated or not) become asymptomatic carrier of Salmonella typhi. This means that they continue to shed bacteria in their faeces for at least a year and after.

DIAGNOSIS

There are multiple methods of diagnosis. Blood culture is the mainstay for the diagnosis of Typhoid fever. It is said, testing the bone marrow is a more reliable method for diagnosing typhoid and is avoided, being a painful procedure.
Whereas, blood, stool and urine samples are collected so they can be checked under the microscope for the presence of Salmonella typhi. This cannot be a confirmatory test in the early stages of disease.
Most acceptable method worldwide are Culture Media and Widal test.
For the recovery of Salmonella from clinical specimen, three general types of media are available.

  • 1-Non-selective media for primary isolation (Blood Agar)
  • 2-Selective or differential agar (e.g. MacConkey Agar, Hektoen Enteric Agar); and
  • 3-Enrichment broths (e.g. Selenite broth)

 

DIAGNOSIS WITH BLOOD CULTURE

Mostly followed Protocol for isolation and identification of Salmonella typhi from blood culture, only by using Non-Selective Media.

1)      Collection of sample:

 

  • (i)- Blood for culture should be taken before patient is given antimicrobial      therapy.
  • (ii)- Patients with a history of fever for 7 to 10 days
  • (iii)- Suggested volume of blood:
  •        From adults: 10-15 ml
  •        From toddlers and preschool children 2-4 ml

2)      Inoculation in Blood Culture Bottle:

  • The optimum ratio of the volume of blood to traditional culture broth is 1:10. For commercial blood culture system please read and use recommended amounts of blood (do not exceed).
  • Blood should be inoculated immediately into a blood culture bottle at the time of drawing blood using same syringe that has been used for collection.

     Blood Culture Bottles which are used for Salmonella typhi are:

PRODUCT CODE PRODUCT NAME Technical Data
TMK 303 BILE BROTH BASE

TMK 332 TRYPTONE SOYA BROTH (SOYA CASEIN DIGEST MEDIUM)

·           Inoculated culture bottles should be incubated at 37°C (Do not refrigerate the sample or keep in cool places during transport).

3)      Further confirmation using Culture Media:

  • Check the inoculated culture bottles for turbidity and other evidence of growth after 1, 2, 3 and 7 days.

  • In case of 1, 2 , and 3 days only, the bottles showing  signs  of  positive  growth  are  cultured  on Blood Agar Plates (TMP 017)*.Also, on  day  7  all  bottles should be sub cultured before being discarded as negative for final confirmation.

  • Subculture plates should be incubated at 37°C for 18-24 hours in an aerobic incubator. If growth is observed in the culture plates, colony morphology should be noted and biochemical tests performed to identify the isolate.

  • *For more detail regarding Sheep Blood Agar Plate kindly click on this link

Salmonella Typhi

Table: Colony Morphology
Microorganisms Haemolytic or Non-Haemolytic Appearance of Colony
Salmonella typhi Non- haemolytic Smooth white colonies
Salmonella paratyphi Non- haemolytic Smooth white colonies

 

4)      Biochemical Test:

S.typhi and S.paratyphi is not the only bacterial pathogen found in the blood, thus to confirm it the presence or absence of S.typhi and S.paratyphi, suspected colonies obtained on sheep blood agar plates are screened by means of following media and test.

Commonly used Biochemical tests for the identification of Salmonella and their results are as following:

Note: V= variable; Alk = Alkaline

Organism

Kliger`s Iron Agar

Motility, Indol Urea

Citrate

Slant

Butt

H2S

Gas

Motility

Indol

Urea

 

S.typhi

Alk

Acid

WK+

-

+

-

-

-

S. Paratyphi A

Ald

Acid

-

+

+

-

-

-

Other Salmonella spp.

Alk

Acid

V

V

+

-

-

V

E. coli

Acid

Acid

-

+

+

+

-

-

Klebsiella spp.

Acid

Acid

-

++

-

V

+

+

Citrobacter spp.

V

Acid

+++

+

+

V

-

+

Proteus spp.

Alk

Acid

+

+

+

V

++

V

*Don’t get confused with Sheep Blood Agar Base, Modified.

Sheep Blood Agar Base, Modified (TMP 018) is used for Bacillus cereus in accordance with ISO 21871:2006. Bacillus cereus is Gram -positive aerobic or facultative anaerobic, motile, spore forming, rod shaped bacterium that is widely distributed environmentally. B.Cereus is associated mainly with food poisoning. It is increasingly reported to be cause of serious and fatal non- gastrointestinal-tract infections.

Click here to read Technical Data of Sheep Blood Agar Base, Modified

 OTHER CULTURE MEDIA, SELECTIVE OR DIFFERENTIAL AGAR AND ENRICHMENT BROTHS ARE COMMONLY USED FOR ISOLATION OF SALMONELLA FROM CLINICAL SPECIMENS

PRODUCT CODE

PRODUCT NAME

COLOUR OF COLONY

TECHNICAL DATA

TM 039

Bismuth Sulphite Agar

Black with metallic sheen

TM 369

Deoxycholate Citrate Agar

Colourless colony with black center

TM 1448

Xylose Lysine Deoxycholate Agar

Good growth, Red with black centers

TM 368

Salmonella Shigella Agar

Colourless with black centers

TM 121

Hektoen Enteric Agar

Black centered colony

TM 489

Wilson Blair Agar Base

Good, black with sheen

TM 1454

Mannitol Selenite broth

Colourless colony, Good recovery on XLD (mixed cultures)

 
Currently, TM Media is supplying Sheep Blood Agar Plate in Delhi NCR region only.
Reference:
  • Crump JA, Mintz ED. Global trends in typhoid and paratyphoid Fever. Clin Infect Dis 2010: 50: 241–246.
  • Mogasale V, Maskery B, Ochiai RL et al. Burden of typhoid fever in low-income and middle-income countries: a systematic, literature-based update with risk-factor adjustment. Lancet Glob Health 2014: 2: e570–e580
  • Singhal L, Gupta PK, Kale P, Gautam V, Ray P. Trends in antimicrobial susceptibility of     Salmonella Typhi from North India (2001-2012). Indian J Med Microbiol 2014: 32: 149– 152.
  • Gautam V, Gupta NK, Chaudhary U, Arora DR. Sensitivity pattern of Salmonella serotypes in Northern India. Braz J Infect Dis 2002: 6: 281–287.
  • Anand PK, Ramakrishnan R. Investigation of the outbreak of typhoid in a village of Thar Desert Rajasthan, India. Indian J Med Res 2010: 131: 799–803.
  • Sathe PV, Karandikar VN, Gupte MD et al. Investigation report of an epidemic of typhoid fever. Int J Epidemiol 1983: 12: 215–219.

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