Morphology, Cultural Characteristics, Pathogenicity, Clinical Manifestations, Laboratory Diagnosis, Prophylaxis, Treatment and Control Measures - Salmonella Typhi (Eberthella Typhi) | 12th Microbiology : Chapter 7 : Medical Bacteriology
Chapter: 12th Microbiology : Chapter 7 : Medical Bacteriology
Salmonella Typhi (Eberthella Typhi)
Salmonella Typhi (Eberthella Typhi)
The genus
Salmonella consists of bacilli that
parasites the intestines of vertebrates and human beings. It causes Enteric fever, which includes Typhoid and Paratyphoid fever. The
most important species of the genus
is Salmonella typhi which causes
typhoid fever.
Morphology
Salmonellae
are Gram – negative rods (1– 3µm× 0.5 µm in size) . They are motile with
peritrichous flagella, non – capsulated and non – sporulated (Figure 7.14).
Cultural Characteristics
They are
aerobic and facultative anaerobe, optimum temperature - 37°C and pH is 7–7.5
They grow
on the following media and show the following characteristic colony morphology
(Table 7.12).
Pathogenicity
Salmonella typhi causes typhoid fever and its pathogenesis is discussed in
flowchart 7.6.
Source of
infection – food, feces, fingers, flies
Route of
entry – faecal oralroute (ingestion)
Incubation
period – 7–14 days
Clinical Manifestations
• The illness is usually gradual, with headache,
malaise (feeling of discomfort), an2orexia (loss of appetite), coated tongue,
abdominal discomfort with either constipation or diarrhea.
• Hepatosplenomegaly
(enlargement of liver and spleen), step ladder pyrexia (continuous fever) and
rose – spots (during 2nd or 3rd week).
Laboratory Diagnosis
Specimens: Blood, stool and urine are the clinical samples collected from typhoid patients. The selection of
relevant specimen depends upon duration of illness, which is very important for
diagnosis (Table 7.13 & Figure 7.15).
The
bacteriological diagnosis of enteric fever consists of the following methods,
which are:
• Isolation
of the bacilli
• Demonstration
of antibodies
Isolation of the bacilli
The
typhoid bacilli are isolatedfrom the following clinical specimens which are
tabulated (Table 7.14).
Demonstration of Antibodies: Slide – agglutination: The isolate is
identified by slide agglutination with ‘O’ and ‘H’ antisera.
Widal Test: It is an agglutination test for detection of agglutinins ‘H’ and ‘O’ in patients with enteric
fever. Salmonella antibodies start appearing in the serum at the end of 1st
week and rise sharply during the 3rd week of enteric fever.
Prophylaxis
Various
types of vaccine and their doses are given in Table 7.15.
Treatment and Control Measures
• Antibacterial therapy has been very effective in
the treatment of patients.
• Ampicillin, amoxicillin and cotrimoxazole are
useful in the treatment of typhoid fever.
• At present, ciprofloxacin is the drug of choice.
• Typhoid
fever can be effectively controlled by sanitary measures for disposal of
sewage, clean water supply and supervision of food processing and handling.
HOTS: Why is proper hand washing considered the most important
element in controlling communicable infections?
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