Veterinary bacteriology

1.  Eberth (1880) - observed S.typhi- mesenteric
nodes and spleen of fatal cases of typhoid fever
 Gaffky (1884) –isolated organism.
 Known as Eberth – Gaffky bacillus or
Eberthella typhi.
 Salmon and Smith (1885) – observed bacillus -
hog cholera in swine. (S.cholerae suis)
 Salmonella currently comprise about 2400
serotypes, of which 50 of them are potentially
pathogenic.
Salmonella - History

2. Host Salmonella
serotypes
Disease
Cattle S.dublin
S.Typhimurium
Enteritis, septicaemia, meningitis
in calves, abortion, osteomyelitis,
joint ill, terminal dry gangrene in
calves.
Enteritis or septicaemia
Pigs S.cholera suis
S. typhisuis
S.typhimurium
Outbreaks clinically similar to
swine fever
Chronic enterits in young pigs
Enteritis or septicaemia
Sheep S.abortus ovis
S.typhimurium
S. brandenburg
Abortion
Enteritis or septicaemia
Abortion
Horse S.abortus equi
S.typhimurium
Abortion in mares
Enteritis or septicaemia

3. Host Salmonella serotypes Disease
Poultry S.pullorum
S.gallinarum
S.arizonae
S.enteritidis,
S.typhimurium and
many other serotypes
Pullorum disease (bacillary
white diarrhoea) in chicks
Fowl typhoid in all ages.
Mainly adults.
Severe enteritis & septicaemia
in chicks, turkey .
Fowl paratyphoid
Human S.typhi
S.paratyphi
(S.paratyphi A)
S.schottmuelleri
(S.paratyphi B)
S.hirschfeldri
(S.paratyphi C)
S.enteritidis &
S.typhimurium
Typhoid fever
Paratyphoid fever
Food poisoning

4.  Intestinal tract of warm blooded and cold-blooded
animals - Reservoir for salmonellae .
 Infected animals become subclinical excretors
results in contamination of water, food and the
environment.
 Survive for 9 months or more in moist soil, water, faecal
particles and animal feeds especially in blood, bone and
fishmeal.
 Salmonella enteritidis - infect the ovaries in poultry and
be transmitted through eggs.
 Undercooked egg dishes may result in human food
poisoning
Habitat

5.  Gram-negative
 Non-capsulated, Non-spore forming
 Short rods, pleomorphic
 Motile by peritrichous flagella except S.gallinarum
and S.pullorum - nonmotile
 possess type –1 fimbriae associated with
mannose sensitive adhesive properties
 Strains of S.gallinarum and S.pullorum form type
2 fimbriae- morphologically and antigenically like
type 1 fimbriae but non-adhesive.
 O and H antigens - major surface antigens, play a
role in disease and immunity.
 H antigens undergo phase variation.
Morphology

6.  Aerobic and facultative anaerobic, growing readily on
simple media, pH : 6.8 – 8.2, temp: 37ºC.
 Nutrient agar : colonies are large, circular, low convex and
smooth.
 Tetrathionate broth, selenite broth and rappaport vasiliadis
medium - selective enriched media.
 Host adapted serotypes from pigs and poultry are more
fastidious than others. do not tolerate selenite broth and
tetrathionate broth. Rappaport is highly suitable.
 Salmonella, except some strains of S.arizonae, are non-
lactose fermenters - produces pale or colorless colonies on
MacConkey agar.
 Give an alkaline reaction in brilliant green agar and have
red colonies.
 XLD medium- produce H2S and have red colonies with a
black center. (Black center with red skirt).
 Salmonella and Shigella agar - colorless colonies with
black center.
Cultural characteristics

7. Growth of Salmonella on MacConkey agar
Pale or colorless colonies on MacConkey agar.

8. Growth of Salmonella on Brilliant green agar
Alkaline reaction and give red colonies.
R.V. medium – left - Positive
Brilliant green – inhibits Gram positive
and Proteus, Pseudomonas, Shigella
Phenol red - indicator

9. Brilliant-green Phenol-red Lactose Sucrose Agar
(BPLS)
Salmonella : The colonies are red
because the bacterium does not
ferment lactose or sucrose.
E. Coli : The colonies are yellow due to
the low pH which is caused by the
production of acid during fermentation
of lactose and/or sucrose.

10. Growth of Salmonella on XLD agar
(Xylose-Lysine –Deoxycholate agar)
Produce H2S and have red colonies with a
black center. (Black center with red skirt).
Deoxycholate, ferric ammonium citrate, sodium thiosulpahte
- selective agents
Xylose fermented by salmonella not by shigella

11. Salmonella – Shigella agar

12. Hektone Enteric agar – S. typhimurium

13. Wilson and Blair’s bismuth sulfite agar
- S. Typhi
Brilliant Green – inhibit Gram positive
Bismuth sulfite- inhibit other Gram negative
enteric bacteria
Jet Black colonies with metallic sheen

14.  IMViC test -, +,-,+.
 Ferment maltose, mannitol, mannose and glucose
and produce acid and gas.
 not ferment lactose, sucrose and salicin.
 Urease –ve.
 Most produce H2S except S.cholerae suis and
S.paratyphi A.
 S. pullorum ferments glucose and rhamnose while
S.gallinarum ferments dulcitiol and maltose.
 In TSI (triple sugar iron) agar - alkaline slant (red),
acid butt (yellow) and superimposed H2S (black)
production. (R/Y/H2S+).
 Test for lysine decarboxylation is positive.
Biochemical characters

15. Typical reaction for salmonellae in TSI (triple sugar
iron) agar is an alkaline slant (red), acid butt (yellow)
and superimposed H2S (black) production.
(R/Y/H2S+).
Growth of Salmonella in TSI agar

16. Salmonella E.coli
Lysine decarboylate test: positive-right

17.  Refrigeration prevents growth but does not kill
bacteria.
 Heating at 55ºC in one hour or at 60ºC in 15mts -
effective in killing the bacteria.
 Boiling or chlorination of water and pasteurization
of milk destroy the bacilli.
 Cultures viable for years if prevented from drying.
 Killed within 5minutes by mercuric chloride
(1:500) or 5% phenol.
 Survives in manure, feces, and pond sediments
Resistance

18.  H or Flagellar antigen
 Heat & alcohol labile
 Strongly immunogenic
 Diphasic – phase I (fliC gene) & II (fljB gene)
 Phase I – Genus or serotype specific, Phase II- non specific
 So far 80 Phase I and 12 Phase II H antigens
 Preserved in 0.2 to 0.4%formaldehyde
 Helpful in identification of serotype
 O or Somatic antigen
 Integral part of the cell wall
 Heat and alcohol stable
 Less immunogenic than H
 So far 67 O antigens have been identified
 Helpful in classification of salmonella
Antigens

19. Surface antigens
 Vi antigen
 Overlying the O antigen
 Related to virulence
 poorly immunogenic
 Present in few serotypes: S.Dublin, S.Typhi, S.ParatyphiC
 Heat labile and alcohol stable
 Helpful in identification of carrier state
 M and N antigens
 Polysaccharide in nature
 Responsible for mucoid nature of colonies
 F or Fimbriae antigen
Antigens

20. Antigenic variations
OH-O variation
 Associated with loss of flagella. ( grown in media with phenol or
by mutation)
Phase variation
 Flagellar antigens of Salmonella occur in 1 or 2 phases. Strains
that posses both phases are called diphasic and strains having
1 phase are called as monophasic.
V-W variation
 Fresh culture agglutinate with Vi antiserum not with O antiserum
– V form
 After repeated subculturing, the Vi antigen is completely lost
and does not agglutinate with Vi antiserum – W form
 Partial loss of the Vi antigen agglutinate with both – VW form
S-R variation
 Smooth to rough variation is associated with the change in
colony morphology
Variation in O antigens
 Changes in the structure of O antigens - due to Phage or
mutation

21. (Reeves, et.al., 1989) - based on DNA homology, host range,
biochemical reactions,
Genus salmonella is divided into two species : S.Enterica and
S.Bongori.
S.enterica is subdivided into 6 subspecies.
 Enterica (I),
Salamae (II),
Arizonae (III a),
Diarizonae (III b),
Indica (IV)
Houtenae (V).
Subgenus Enterica is the largest and most important,
containing all the species that commonly cause human and
animal infections.
Members of this subgenus are given a name like
S.enterica sub sp enterica serovar Typhimurium.
Classification of Salmonella

22. O
serogroup
* Serotype
Antigens
O
H
Phase 1 Phase II
2 A Paratyphi A 1,2,12 a -
4 B
Paratyphi B
Typhimurium
1,4,5,12
1,4,5,12
b
c
1,2
1,2
7 C
Cholera suis
Paratyphi C
6,7
6,7 (W)
c
c
1,5
1,5
9 D
Typhi
Enteritidis
Pullorum and gallinarum
Dublin
9,12 (W)
1,9,12
1,9,12
1,9,12 (Vi)
d
g, m
-
g, p
-
1,7
-
-
Kauffmann –white scheme
Based on O and H antigens and agglutination reactions.
Phage typing : 97 Vi II Phage type of S.Typhi,
Phage types E1, O and A are most common in India
Biotyping : 144 different biotypes of S.Typhimurium

23. Virulence Factors
• Fimbriae
• Salmonella pathogenicity islands - 18 nos - Chromosome
and plasmid encoded
 Type III secretion system :
20 proteins – secretion of virulence factors of salmonella into
host cells- mediate uptake of the bacteria into epithelial
cells
 Salmonella pathogenicity islands (SP-1): non phagocytic
cell invasion
 SP2 : survival and replication within macrophages
 Endotoxin
 Acid tolerance gene: from stomach acids & pH in
phagosome
 Enzymes: Catalase and superoxide dismutase- protect
from intracellular killing in macrophages

24. Salmonella infection in animals –
outcome
• Subclinical faecal excretors- all ages
• Latent carriers – all age
• Acute or chronic enteric disease- all ages -
Enterocolitis with fever, depression,
anorexia, profuse foul smelling diarrohea
containing blood, mucus, epithelial shreds,
casts
Dehydration, weight loss and abortion
Acute followed by chronic – intermittent
fever , soft faeces and weight loss

25. • Septicaemia – all ages
 most common in young ones
 Potentially fatal disease with sudden onset, high fever,
depression, recumbency
 Die within 48 hrs
 In survive- persistent diarrohea, arthritis, meningitis or
peumonia
• Abortion
• Joint ill – calves – septicaemia / umbilical infection
• Osteomyelitis
 Young animals -Cervical vertebrate, bones of the distal
limb- leads to spinal cord compression
 Terminal dry gangrene – local ischemia, gangrene – hind
limbs, ears and tail

26. Salmonella abortion in sheep
Bovine: small intestine. The mucosa is
reddened and covered by large yellow-
brown casts of fibronecrotic exudate.
Pig: The intestinal lumen
has reddened erosions and
a fibrinonecrotic exudate.
Pig: The mesenteric lymph node is
enlarged and edematous.

27. Pullorum disease (S.pullorum)
 Important poultry disease.
 Infection spreads both vertically and horizontally.
 Fluff and faeces of infected contain S.pullorum.
 Faeces of infected contaminates the feed and water that
act as a source of infection.
 Chick boxes, litter, utensils and chick sexers also spread
the infection. Droplet infection is also reported.
 Young chicks : more affected with a morality of up to 95%.-
Bacillary white diarrhoea
 sleepy, dull and huddle close to the heating source
 Inappetance, increased thirst, respiratory distress
 nervous Symptoms - staggering gait & incoordination of the
limbs.
 Vent covered with adherent mass of faeces.
 Growers- Growth rate is slow with intermittent diarrhoea.
 Adults: decreased egg production is the most important
symptom.

28. Swelling of the joint and synovitis

29. Lesions
In chicks
congestion of spleen, yellow colouration of spleen with
streaks of haemorrhage, hyperaemia of liver, necrotic foci
on kidney, spleen, distended ureters with urates,
distended caeca and degeneration of the myocardium.
 In adult : Misshaped ovules and detachment of ovules
Diagnosis
Based on symptoms and lesions.
Rapid Whole blood test: identify carrier adult birds.
Isolation of the causative organism by culturing.
Control
 Identification of the reactors and removing them from flock.
 Periodical disinfection of the incubators using
formaldehyde vapour (fumigation).
 Fumigation of egg or dipping them in bactericidal agents
before incubating them.
Pullorum disease (S.pullorum)

30. Grayish white nodes in gizzard and heart
Whitish nodes in lung
Follicles are deformd and thick
pendulating masses Fibrinous adhesive peritonitis

31. Salmonella – Rapid plate agglutination test

32.  Affects adult birds and growers.
 Vertical transmission from hen to chicks.
 By ingestion.
 Survive in litter for a long time and acts as source of infection.
Symptoms
Chicks : symptoms are as same as pullorum disease.
Mortality in adults : up to 50%.
Affected birds show listlessness, green coloured faeces,
purple colouration of comb and wattles, anaemia and
intermittent diarrhoea.
Lesions
 Enlarged liver that turns into dark red or reddish brown after
exposure to atmosphere.
 Enlargement of spleen, focal necrosis on liver, spleen and
myocardium are other lesions.
 Intestine may show catarrhal inflammation and petechial
haemorrhage.
Diagnosis
 Based on symptoms and lesions.
 Rapid whole blood test.
 Isolation by culturing.
Fowl typhoid (S.gallinarum)

33. Fowl typhoid
Enlarged liver and spleen that turns into reddish brown
after exposure to atmosphere
Enlarged bronze greenish tint liver - pullorum

34.  Main mode of spread is through eggs. Organisms
enter into the egg through contaminated shell and
spread the infection.
 By ingestion, inhalation and through fomites.
Symptoms- as same as pullorum disease.
Lesions
 Congestion and necrosis of spleen with catarrhal
enteritis.
Diagnosis
 Symptoms and lesions are indistinguishable from
pullorum disease. Hence the agglutination reactions
offer conclusive diagnosis.
 S. enteritidis- food poisoning
Avian paratyphoid (S.typhimurium)

35. Immunity and therapy
 Immunity is cell mediated because organisms are
intracellular
 Vaccines for pigs and calves but efficacy is not high
 Antibiotics can be used particularly for septicemia.
 Most of the pathogens are intracellular, antibiotics
can easily fail.
 Diarrhea usually is self-limiting and in older animals
usually does not lead to death.
 Fluid replacement can be used to reverse severe
dehydration