Salmonella basics

This slide is particularly useful for undergraduate medical and nursing students.

1. Salmonella
Shyam Kumar Mishra
1

2. •Family- Enterobactereciae
•Most strains are motile
•Usually produce both acid and gas from glucose, mannitol
and sorbitol
•Urease – Negative
•Phenyldeaminase test – Negative
•Usu. form H
2
S on TSI agar
•Citrate is utilized as the sole source of carbon (with few
exceptions)
•Lysine and ornithine decarboxylase test +
•G+C content of DNA – 50-53 mol%
•Type species – Salmonella enterica
2

3. 2 species
•S. enterica
–6 subspecies
•enterica-------------- >2500 serotypes (at least 2541)
•salamae
•arizonae
•diarizonae
•houtenae
•indica
•S. bongori
3

4. Morphology of Salmonella
•Gram negative
bacilli
•1-3 x 0.5 micron,
•Motile by
peritrichous
flagella
4

5. Cultural Characters
•Aerobic / Facultatively anaerobic
•Grows on simple media – Nutrient agar
•Temp 15 – 41ºc / 37º c
•Colonies appear as large 2 -3 mm, circular, low
convex
•On MacConkey medium appear Colorless (NLF)
•Wilson Blair Bismuth sulphide medium- black
colonies
•Salmonella-Shigella (SS) agar
H
2
S produced by Salmonella Typhi
5

6. Salmonella on XLD agar
6

7. Enrichment Medium
Liquid Medium
•Selenite F medium
•Tetrathionate broth
–Particularly stool specimens..
7

8. Biochemical Characters
•Glucose, Mannitol, Maltose produce A/G
(Salmonella Typhi do not produce gas)
•Lactose/Salicin/sucrose not fermented.
•Indole –
•Methyl Red +
•V P -
•Citrate + (S. Typhi -)
•Urea –
•H
2
S – produced by S. Typhi
(Paratyphi A do not produce H
2
S)
8

9. S. Typhi Biochemical reaction
9

10. Antigenic structure of Salmonella
•Somatic or 0 Antigens - Granular deposit (Felix tube)
• Flagellar or H Antigens - Loose and cotton-woolly
clumps (Dreyer’s tube)

10

11. Other antigens
•Vi – Surface antigen in some species only
–Typhi, Paratyphi C, Dublin
•F- Fimbrial antigen
–Preserved in 0.1% formaldehyde
•M antigen – loose extracellular polysaccharide slime
•R antigen – S R variation
11

12. Kauffmann – White scheme
•Serotype 0 antigens H antigens
Phase 1 2
Typhi 9,12[Vi] d -
Paratyphi A 1,2,12 a [1,5]
12

13. Antigenic Variation in
Salmonella
•H O variation
•Phase variation
•V W variation
•S R variation
•Variations in O antigen
13

14. Virulence factors
•Fimbriae
•Salmonella pathogenicity island (Spi) and Type III
secretion system
•Endotoxin
•Invasins
•Virulence antigen (Vi)
•Acid tolerance response (ATR) gene
•Plasmid
•Property of lysogenic conversion
14

15. Salient features of Salmonella
•Intracellular multiplication
•Resistance to bile
•Produces endotoxin
15

16. Salmonellosis
•S. Typhi.
•S. Paratyphi A, B and C
•Other salmonellae
Important clinical syndromes :
Enteric fever, Septicemias, gastroenteritis.
16

17. Enteric Fever
Typhoid
•Typhoid – caused by S. Typhi
•Paratyphoid Caused by
Paratyphi A,B,C
•Infective dose ID
50
/ 10
7

17

18. Pathology and Pathogenesis
18
•Bacilli enter through
ingestion,
•Bacilli attach to microvilli,
ileal mucosa, penetrate to
lamina propria and sub
mucosa
•Phagocytosis by
Polymorphs and
Macrophages
•Enters the mesenteric
lymph nodes
•Enter the thoracic duct –
Blood stream

19. 19

20. 20
Ingestion of
salmonella
Small
intestine
Mesenteric
LNs
Transient
bacteremia
Multiplication in
macrophages in
liver, spleen and
BM
Gall
bladder
Signs and
symptoms
Bile
L
y m
p
h
a
t i c
s
T
h
o
r a
c
i c
d
u
c
t
Bile
Septicaemia
Cholecystitis,
Carrier state
Inflammation and
ulceration of
Peyer’s patches
Diarrhoea,
hemorrhage,
perforation
Incubation
period

21. Pathology and Pathogenesis
•Bacteremia Spread to Liver, Gall
bladder, Spleen, Bone marrow,
Lymph nodes, Lungs, Multiply in
kidneys
Once again spill into Blood stream
Causes clinical illness.
21

22. Pathology and Pathogenesis
•Multiply abundantly in Gall bladder,
•Bile rich source of Bacteria
•Spill into Intestine, infects peyers patches,
Lymph follicles
•Inflammation – Undergo necrosis, Slough off
•Typhoid ulcers
•Typhoid ulcers can cause perforation and
hemorrhage
•Duration of Illness 3 – 4 weeks
•Incubation 7 -14, ( 3-56 days )
22

23. Clinical manifestation
•Headache, malaise, anorexia, coated tongue
•Abdominal discomfort,
•Constipation / Diarrhea
•Step ladder type fever,
•Relative bradycardia,
•A soft palpable spleen
•Hepatomegaly
•Rose spots appear
23

24. Complications of Enteric fever
•Intestinal perforation,
•Hemorrhage,
•Circulatory collapse.
•Bronchitis Bronchopneumonia,
•Meningitis,
•Cholecystitis,
•Arthritis, Periostitis, Nephritis,
•Osteomyelitis
24

25. Epidemiology
•Source an active patient or a Carrier shed the
Bacilli.
•Convalescent carrier - 3 weeks to 3 months
Temporary carrier - 3 months to 1 year
Chronic carrier > 1 year
25

26. Typhoid Mary
•A famous example is
“Typhoid Mary” (Mary
Mallon), who was a
food handler
responsible for several
typhoid outbreaks
26

27. Laboratory Diagnosis of
Typhoid Fever
•Isolation of Bacilli (Gold standard)

•1
st
Week – Rose spot, Blood culture, Bone marrow
culture
•2
nd
Week – Widal test
•3
rd
Week – Stool culture
•4
th
Week –Urine culture
27

28. Blood Cultures in Typhoid FeversBlood Cultures in Typhoid Fevers
•Bacteremia occurs early
in the disease
•Blood Cultures are
positive in
1
st
week in 90%
2
nd
week in 75%
3
rd
week in 60%
4
th
week and later in 25%
28
• Draw 5 – 10 cc of Blood by venipuncture.
• Add to 50 -100 ml of Bile broth.
• Incubate at 37 c /Subculture in MacConkey at regular intervals

29. Castaneda’s method of
Blood Culture
•Double medium used Solid/Liquid medium in
the same Bottle.
•Bottle contains Bile broth/agar slant,
•Reduces the chances of contamination
•Increases the chances of isolation.
29

30. Salmonella on Mac Conkey's agar
30

31. Clot culture
•Clot cultures are more
productive in yielding
better results in
isolation.
•A blood after clotting,
the clot is lysed with
Streptokinase ,but
expensive to perform
in developing
countries.
31

32. Bactek and Radiometric based methods
are in recent use
•Bactec methods in
isolation of Salmonella
is a rapid and sensitive
method in early
diagnosis of Enteric
fever.
32

33. Biochemical Characters
•??????
33

34. Slide agglutination tests
•In slide agglutination
tests a known serum
and unknown culture
isolate is mixed,
clumping occurs within
few minutes
•Polyvalent – To know
whether it is salmonella
or not
34
• Monovalent sera- To identify the serotype of Salmonella

35. Culturing other Specimens
•Faeces - Enrichment in Tetrathionate
broth and Selenite broth
•Culturing in MacConkey/DCA/Wilson
Blair medium – Large black colonies.
•Urine Culture – positive in 25 %
•Other samples
Bone Marrow, Bile
35

36. Serology
•WIDAL Test –(Tube agglutination test)
•Detects O and H antibodies
•Diagnosis of Typhoid and Paratyphoid
•Testing for H agglutinins in Dreyers tubes, a
narrow tube floccules at the bottom
•Testing for O agglutinins in Felix tubes, Chalky
•Incubated at 37º c overnight
36

37. Widal test (Tile method)
Significance
•1st week negative.
•Titers rise in 2nd week.
•Rise of titers diagnostic
•Single test not diagnostic.
•Paired samples tests
•Diagnostic.
O > 1 in 80
H > 1in 160
H agglutinins appear first (H
antigen is highly
immunogenic)
37

38. Limitation of Widal Test
•The Widal test is time
consuming (Tube
method)
•Anamnestic reaction
38

39. Diagnosis of Carriers and
Environments
•Fecal carriers by isolation from
specimens or Bile aspirated.
•Antibody to Vi antigen (1:10 or above)
•Sample from sewage
39

40. Vaccines
•TAB vaccine
S. Typhi 1,000 millions
S Paratyphi A,B 750 millions.
Injected subcutaneously 0.5 ml at 4 – 6 weeks.
•Live oral (Ty2 1a) typhoid vaccine
•Purified Vi polysaccharide vaccine (Vi CPS)
40

41. Treatment
•Chloramphenicol
•Ampicillin
•Cotrimoxazole
•Fluoroquinolones
•Ceftriaxone
•Azithromycin
41

42. THANK YOU
42