Salmonella is a gram-negative rod-shaped bacteria. There are over 2400 serotypes, with some causing typhoid fever in humans (Salmonella enterica serotypes Typhi, Paratyphi A, B, C) and others causing food poisoning (Salmonella enteritidis, S. typhimurium). Salmonella has flagella, is facultatively anaerobic, and grows well at 37°C. Identification involves culture, biochemical testing, and serotyping. Salmonella can cause typhoid fever through ingestion, initially infecting the intestines before spreading systemically. Left untreated, typhoid fever can last weeks and cause complications. Vaccines and improved sanitation help control typh

1. SALMONELLA

2. MORPHOLOGY
• Gram negative rods, 1-3
µm x 0.5 µm,
• Motile with peritrichate
flagella (except for
S. gallinarum, S
pullorum) which is
always NM
• No capsule or spores
• May possess fimbriae

3. • 2463 species
• Enteric fever group : typhoid and paratyphoid
bacilli exclusively or primarily human
pathogen. S. enterica : serotypes Typhi,
Paratyphi A, B, C
• Non typhoidal : Food poisoning group
essentially animal parasites but which can also
infect human beings, producing
gastroenteritis, septicemia or localised
infections. Eg. S.enteritidis, S. typhimurium

4. Cultural Characteristics
• Aerobic and facultative anaerobic
• Media of pH 6.8
• Temp ranges from 15-40° C (opt 37°C)
• Colonies are large, 2-3mm in diameter, circular,
low convex and smooth
• More translucent than coliform colonies
• MA, DCA – NLF colourless colonies
• Wilson and Blair bismuth sulphite media : black
colonies with a metallic sheen due to production
of H2S ( S paratyphi A gives green colonies)

6. Biochemical reactions
• Ferment glucose, mannitol and maltose
(acid+gas). Exception is S Typhi which is
anaerogenic
• Lactose, sucrose and salicin : not produced
• Indole is not produced
• MR positive, VP negative
• Citrate : utilised (except Typhi and Paratyphi)
• Urea is not hydrolysed
• H2S is produced except by S Paratyphi A,
S. cholerasuis

7. RESISTANCE
• Killed at 55 C in 1hr or at 60 C in 15 mins
• Boiling or chlorination of water and
pasteurization of milk destroy the bacilli
• In polluted water and soil, they survive for
weeks and in ice for months
• If prevented from drying culture survive for yrs
• Killed within 5 mins by 5% phenol

8. ANTIGENIC STRUCTURE
• Flagellar antigen : H
• Somatic antigen : O
• Surface antigen : Vi

9. H ANTIGEN
• Present on the flagella
• Heat labile
• Destroyed by boiling or by treatment with
alcohol but not by formaldehyde
• When mixed with antisera, large loose fluffy
clumps of agglutinate
• Immunogenic, antibody in high titre following
infection or immunisation

10. O Antigen
• Somatic O antigen is a phospholipid-protein-
polysachharide complex
• Integral part of the cell wall
• Identical to endotoxin
• extracted by treatment with trichloroacetic acid
• Unaffected by boiling, alcohol or weak acids
• When mixed with antisera, suspension forms
compact chalky, granular clumps
• Less immunogenic and the titre of antibody is
generally lower
• Classified into no of groups based on the
characteristics O antigens on the bacterial surface

11. Vi antigen
• Surface Polysachharide antigen enveloping the
O ag
• Heat labile analogus to the K antigens of
coliform
• bacilli inagglutinable with the O antiserum
become agglutinable after boiling or heating
at 60 C for 1 hr
• Unaffected by alcohol or 0.2% formal

12. Vi Antigen
• Tends to be lost on serial subculture
• Acts as a virulence factor by inhibiting
phagocytosis, resisting complement activation
and bacterial lysis by the alternative pathway
and peroxidase mediated killing
• Poorly immunogenic
• Persistence of Vi antibody indicates the
development of the carrier state.

13. Pathogenicity
• S Typhi, S Paratyphi A and B : human sources
• Enteric fever
• Septicemia
• Gastroenteritis or food poisoning

14. Virulence factors
• Type III secterion system (bacterial proteins):
mediate initial invasion
• O antigen: endotoxin
• Vi antigen
• Invasins: adherence, penetration

15. ENTERIC FEVER
• Infection acquired by ingestion
• Infective dose : 103 to 106 bacilli
• Incubation period: 7-14 days (3-56)
• On reaching the gut, the bacilli attach
themselves to the lamina propia and
submucosa
• Phagocytosed by macrophages and polymorphs
• Ability to resist intracellular killing and to
multiply within these cells

16. • Enter the mesenteric LNs where they multiply
and via thoracic duct enter the bloodstream
• Transient bacteremia follows during which the
bacilli are seeded in the liver, gall bladder, spleen,
BM, LNs, lungs and kidneys where further
multiplication takes place
• Towards the end of the incubation period (10th),
there occurs massive bacteremia (secondary
bacteremia) from these sites of multiplication,
heralding onset of clinical disease

17. • Bile : multiplies abundantly in the GB and is
discharged continuously into the intestine
where it involves the Peyers patches and
lymphoid follicles of the ileum
• They become inflamed, undergo necrosis and
slough off, leaving behind the characteristic
typhoid ulcers
• Ulceration : intestinal perforation and
hemorrhage

18. E N T E R I C ( T Y P H O I D ) F E V E R
• Typhoid fever has a slow, insidious onset and
if untreated, lasts for weeks. It ends either by
a gradual resolution or in death due to
complications (eg, rupture of the intestine or
spleen).
• Inc period : 7-14 days ( 3-56days)
• Clinical course : mild undifferentiated pyrexia
(ambulant typhoid) to a rapidly fatal disease

19. • Onset is ususally gradual, with headache,
malaise, anorexia, a coated tongue and
abdominal discomfort with either constipation or
diarrhea
• Step ladder pyrexia with relative bradycardia and
toxemia
• Hepatomegaly
• Soft palpable spleen
• Rose spots (3rd -4th wk)

20. • Complications :
• Perforation, hemorrhage, circulatory collapse
• Cholecystitis, arthritis, abscesses, periosteitis,
nephritis, hemolytic anemia, venous
thromboses, peripheral neuritis
• Some develop psychoses, deafness or
meningitis
• Convalescence is slow
• In about 5-10% relapse occur

21. • S. paratyphi A and B cause paratyphoid fever
which resembles typhoid fever but is generally
milder

22. EPIDEMIOLOGY
• Typhoid fever : still an important cause of
morbidity and mortality worldwide
• Strictly a human disease
• Chronic carriers of serotype Typhi are the
primary reservoir.
• The pathogen can be transmitted in the water
supply in developing endemic areas or where
defects in any system allow sewage from
carriers to contaminate drinking water.
• Transmission is by the fecal–oral route.

23. • Pt who continue to shed typhoid bacilli in
feces for 3 wks to 3 months after clinical cure :
convalescent carriers
• Those who shed the bacilli for more than 3
mths but less than 1 yr : temporary carriers
• Over a yr : chronic carriers (2-4%)
• Some persons may become carrier following
inapparent infn : symptomless excretors

24. • Food handlers or cooks who become carriers
are particularly dangerous
• Mary Mallon (Typhoid Mary) : over a period of
15 yrs caused at least 7 outbreaks affecting
over 200 persons

26. Laboratory Diagnosis
• Isolation of the organism from the patient
– Blood culture
– Stool culture
– Urine culture
– Others- bile, duodenal juice
• Demonstration of antibodies
• Demonstration of antigen in blood or urine

27. BLOOD CULTURE
• +ve in 90% of the cases in 1st wk, 75 % in 2nd
wk, 60% in 3rd wk and 25% in 4th wk. Becomes
negative on treatment with antibiotics
• 5-10ml of blood in 50-100ml of bile broth (
BHI broth, glucose broth)
• Sodium polyanethol sulphonate counteracts
the bactericidal action of blood

28. • Incubation at 37C overnight , subcultured on
MacConkey agar
• Pale NLF colonies may appear
• Motility and biochemical test
• Identification of the isolate is confirmed by
slide agglutination

29. SLIDE AGGLUTINATION
• A loopful of the growth from an agar slope is
emulsified in 2 drops of saline on a slide
• If S typhi is suspected, a loopful of typhoid O
antiserum ( factor 9/group D) is added
• Agglutination is looked for
• If suspected of S paratyphi, then agglutination is
done with O and H antisera

30. • If not isolated from 1st subculture from bile
broth, subcultures should be repeated every
other day till growth is obtained
• Cultures should be declared negative only
after the incubation for 10 days
• Castaneda’s method : to avoid contamination
and also for economy and safety
• Clot culture yields higher rate of isolation

31. FECES CULTURE
• Org. shed throughout the disease and also
during convalescent
• Almost as valuable as blood culture
• Use of enrichment (tetrathionate or selenite
broth) and selective media
• Usually helpful in isolation of the patient with
antibiotics
• Plated to MacConkey, DCA and Wilson Blair
media

32. URINE CULTURES
• Salmonella are shed in urine infrequently and
irregularly
• Less useful
• Cultures are positive only in 2nd and 3rd wk
• Repeated sampling improves the rate of
isolation
• Clean voided urine samples are centrifuged
and the deposit inoculated into enrichement
and selective media

33. Demonstration of Antibodies
(WIDAL TEST)
• Test for the measurement of O and H
agglutinins for typhoid and paratyphoid bacilli
in the patients sera
• 2 types of tubes :
• Dreyers tube : a narrow tube with a conical
bottom for the H agglutination
• Felix tube : short round bottomed tube for O
agglutination

34. Dreyers tube

35. Widal test
• Equal volumes of serial dilution of serum and the
H and O Ag are mixed and incubated in a water
bath at 37 C overnight
• Agglutination titre of the serum are read
• H agglutination : loose, cottony woolly clumps
• O agglutination : disc like pattern at the bottom
of the tube
• Supernatant is clear in both
• Antigens used are O and H antigens of S typhi and
H antigens of S Paratyphi A and B

37. Widal test Interpretation
• Agglutination titre depend on the stage of the
disease
• Testing of 2 or more samples is more meaningful
than a single test ( rise in titre)
• Difficult to lay down the level of significance
though 1:80 for O and 1:160 for H
• Agglutinins are present on account of prior
disease, inapparent infection or immunisation

38. • Persons who have had prior infection or
immunisation may develop an anamnestic
response during an unrelated fever. This may
be differentiated by repetition of the test after
a wk. (transient rise)
• Bacterial suspensions used as antigens should
be free from fimbriae ( False positive results)
• Cases treated early with chloramphenicol may
show a poor agglutinin response

39. Demonstration of Circulating Antigen
• Sensitised Staphylococcal coagglutination test
• Staph aureus (Cowan I strain) containing protein
A is stabilised with formaldehyde and coated with
S typhi antibody
• When 1% suspension of such sensitised
staphylococcal cells are mixed with serum from pt
in the 1st wk of the disease = visible
agglutionation within 2 minutes

40. Prophylaxis and Treatment
• Improvements in sanitation
• Detection of carriers
• Provision of protected water supply
• Chloramphenicol
• Fluoroquinolones
• Third generation cephalosporins

41. Vaccines
1. Killed whole cell vaccine :
– Heat killed, phenol preserved, whole cell
containing mixture of S. Typhi and S Paratyphi A
and B (TAB)
– Injected s/c in 2 doses of 0.5ml each at an
interval of 4-6 wk followed by a booster dose
every 3 yrs
– Effication 60-70% protection for 3-7 years
2. Vaccines of purified Vi antigen :
– Contains purified Vi ag which is injected
intramuscularly in a dose of 25µg (typhim- vi)-
75%

42. 3. Live vaccine:
• live avirulent vaccine from a mutant strain of S. typhi
(Ty2 1a)
• to children
• Efficacy : 65- 96%
• 3 oral doses on alternate day one hour before food
with a glass of milk

43. Salmonella Gastroenteritis
• Food poisoning caused by any Salmonella
except S Typhi
• Source of infection : animal products
• S Typhimurium, S enteritidis, S. anatum, S
haldar, S heidelberg
• Results from contaminated food
• Eggs, egg products, meat, milk and milk
products

44. Gastroenteritis
• Disease develops after a short inc period of 24
hrs or less, with diarrhea, vomiting, abdominal
pain and fever.
• May vary in severity from the passage of one or
two loose stools to an acute cholera like disease
• Usually subsides in 2-4 days but in some cases a
more prolonged enteritis develops, with passage
of mucus and pus in feces, resembling dysentery

45. Laboratory diagnosis
• Isolating the organism from the feces
• In outbreaks, causative article of food can
often be identified by taking a proper history
• Isolation of salmonella from the article of food
confirms the diagnosis

46. Control
• Prevention of food contamination
• Proper cooking destroys salmonella
• Large problem in developed countries largely
because of their food habits and living
conditions

47. Salmonella septicemia
• S choleraesuis may cause septicemic disease
with focal suppurative lesions such as
osteomyelitis, deep abscesses, endocarditis,
pneumonia and meningitis
• Can be isolated from blood or pus
• Should be treated with chloramphenicol or
other antibiotics as determined by sensitivity
tests.

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