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Questions and Answers
What is the primary reservoir of Salmonella organisms in asymptomatic carriers?
What is the primary reservoir of Salmonella organisms in asymptomatic carriers?
What is the purpose of the Kauffmann-White classification?
What is the purpose of the Kauffmann-White classification?
What is the characteristic of Salmonella in terms of its oxygen requirements?
What is the characteristic of Salmonella in terms of its oxygen requirements?
What is the characteristic of Salmonella in terms of lactose fermentation?
What is the characteristic of Salmonella in terms of lactose fermentation?
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What is the characteristic of Salmonella in terms of urease production?
What is the characteristic of Salmonella in terms of urease production?
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What is the typical manifestation of enteric fever caused by Salmonella Typhi?
What is the typical manifestation of enteric fever caused by Salmonella Typhi?
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What is the polysaccharide layer covering Typhi isolates outside the cell wall?
What is the polysaccharide layer covering Typhi isolates outside the cell wall?
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What is the temperature at which the heat labile antigen can be removed by heating the bacterial suspension?
What is the temperature at which the heat labile antigen can be removed by heating the bacterial suspension?
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What is the primary method of lab diagnosis for Salmonella infection?
What is the primary method of lab diagnosis for Salmonella infection?
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What is the purpose of using Selenite F broth and Tetrathionate broth?
What is the purpose of using Selenite F broth and Tetrathionate broth?
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What is the method used to obtain the alternative phase of H antigen?
What is the method used to obtain the alternative phase of H antigen?
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What is the primary use of Widal test in Salmonella diagnosis?
What is the primary use of Widal test in Salmonella diagnosis?
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Which of the following antibiotics is never used in the treatment of Salmonella?
Which of the following antibiotics is never used in the treatment of Salmonella?
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What is the primary treatment for uncomplicated Salmonella food poisoning/gastroenteritis?
What is the primary treatment for uncomplicated Salmonella food poisoning/gastroenteritis?
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Study Notes
Clinical Syndromes of Salmonella
- Enteric fever (typhoid fever) is a systemic illness caused by S. Typhi and S. Paratyphi A, B, and C.
- Gastro-enteritis and food poisoning are characterized by vomiting, diarrhea, fever, and abdominal pain.
- Bacteraemia is a common feature of enteric fever, but rare with other strains.
Characteristics of Salmonella
- Gram-negative bacilli, non-capsulate, non-sporing.
- Oxidase negative, aerobic and facultative anaerobic.
- Grow on a wide range of simple media, motile, and non-lactose fermenting.
- Urease negative.
Antigenic Structure (Kauffmann-White Classification)
- Serotyping is done according to O (cell wall) and H (flagellar) antigens.
- Detected by agglutination test with specific antisera.
- Each Salmonella strain is described as a formula with three parts: O antigens, Hantigens phase 1, and Hantigens phase 2.
Examples of Kauffmann-White Classification
- S. Typhi: O antigens: 9,12, Hantigens phase 1: d, Hantigens phase 2: -
- S. Paratyhi A: O antigens: 1, 2, 12, Hantigens phase 1: a, Hantigens phase 2: 1,5
- S. Enteritidis: O antigens: 1, 9, 12, Hantigens phase 1: g, m, Hantigens phase 2: 1,7
Vi Antigen
- Almost all S. Typhi isolates have a covering polysaccharide layer outside the cell wall, known as the Vi antigen.
- May cause O antigen to be undetectable by agglutination test.
- Heat labile antigen that can be removed by heating the bacterial suspension for 1 hour at 100°C.
Laboratory Diagnosis
- Isolation of the organism from patient's blood, faeces, urine, or vomit.
- Culture media: blood agar, MacConkey agar, xylose lysine deoxycholate (XLD) agar, salmonella shigella (SS) medium, deoxycholate citrate agar (DCA).
- Enrichment broths: Selenite F broth, Tetrathionate broth.
- Identification: culture characteristics, motility, biochemical tests, serotyping by latex agglutination, and serotyping by slide agglutination.
H Antigen Phase Conversion
- In many Salmonellae, production of H antigen is diphasic, with strains varying spontaneously and reversibly between two phases with different sets of antigens.
- Definitive identification requires the detection of antigens of both phases.
- The alternative phase can be obtained by selective culture of the isolate in semi-solid agar containing monophasic antiserum to the original phase antigens.
Serological Diagnosis by Widal Test (SAT)
- Standard agglutination test to detect Salmonella antibodies in patient's serum.
- In diagnosis of enteric fever, but not useful in Salmonella food poisoning.
- Patient's serum is tested by tube agglutination for titers of antibodies against H, O, and Vi antigens.
Treatment
- Ciprofloxacin (always with nalidixic acid disk for extra-intestinal isolates).
- Chloramphenicol, ampicillin, cotrimoxazole, and ceftriaxone/cefotaxime.
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Description
Learn about the clinical syndromes of enteric fever, including typhoid fever, gastroenteritis, and bacteraemia, as well as the asymptomatic carrier stage and characteristics of the infection.
