2. Sub-grouping
LACTOSE FERMENTING NON-LACTOSE
(PINK PIGMENT IN MAC FERMENTING
AGAR) (NO PINK PIGMENT IN
MAC AGAR)
1. ESCHERICHIA 1. SALMONELLA
2. KLEBSIELLA 2. SHIGELLA
3. ENTEROBACTER 3. PROTEUS
4. CITROBACTER 4. MORGANELLA
5. PROVIDENCIA
6. SERRATIA
3. Morphology
Belongs to Gamma Proteobacteria
Gram negative
Rods
1-4 X 0.6µm
Non-sporing
Have simple nutrition requirements
Facultative anaerobes
4. Important bacterial group, they are called enteric
bacteria as it reflects the fact that they inhabit the
intestinal tracts of humans and other animals.
Differentiation is based on biochemical reactions and
differences in antigenic structure
5. Motility
Mostly surrounded by flagella (peritrichous) and are
motile
Non-motile enterobacteriaceae are Shigella and Klebsiella
In Escherichia and Morganella, most of the strain are
motile, but some are non-motile
Special case like Yersinia, contain species that are motile
at 25oC but non-motile at 35 – 37oC.
7. Culture
Most will grow in wide temperature range in ordinary
culture media including NA and BA and selective
media.
The selective media is incorporated with dyes and
bile salts that inhibit G+ organisms and may suppress
the growth of nonpathogenic species of
Enterobacteriaceae
Eg: Selective media is required to recover Salmonella
and Shigella On BA, enterobacteria produce large,
shiny, grey colonies that may be hemolytic. Most grow
well on a variety of lab media including a lot of
selective and differential media originally developed
for the selective isolation of enteric pathogens
8. Enterobacteriaceae
Many are differential on the basis of whether or
not the organisms ferment lactose and/or
produce H2S. Species that produce hydrogen
sulphide often show a green colour around the
subsurface colonies (Klebsiella) and capsulated
strains (Escherichia) produce large mucoid
colonies.
Catalase reaction vary among
Enterobactericeae
12. Toxin production
Exotoxin (enterotoxin) is produced by
Shigella dysenteriae and toxigenic strain
of Escherichia coli (ETEC)
When lysed, enterobacteria will release
endotoxin from their cell wall
*The feature above is applied to all Gram
negative rods
13. Enterobacteriaceae
On CBA they all produce similar colonies
that are relatively large and dull gray. They
may or may not be hemolytic.
The three most useful media for screening
stool cultures for potential pathogens are
TSI, Lysine iron agar (LIA), and urea or
phenylalanine agar.
The antigenic structure is used to
differentiate organisms within a genus or
species.
Three major classes of antigens are found:
14. Enterobacteriaceae
Somatic O antigens – these are the heat stable
polysaccharide part of the LPS.
Variation from smooth to rough colonial forms is
accompanied by progressive loss of smooth O Antigen.
Flagellar H antigens – are heat labile
Envelope or capsule K antigens – overlay the surface O
antigen and may block agglutination by O specific
antisera.
Boiling for 15 minutes will destroy the K antigen and unmask
O antigens.
The K antigen is called the Vi (virulence) antigen in
Salmonella typhi.
17. Assignments
Prepare notes on each of genus under
enterobacteriaceae group. (10 genus)
All the notes should have the following
criteria:
a) morphology,b)culture, c)biochemical
tests d) serology test
Submit on 3rd of September 2012
19. Main species
Brucella melintensis
Brucella abortus
Brucella suis
20. Normal habitat
Obligate intracellular pathogens of
animals
B. melitensis mainly found in goat and
sheep
B. abotus infects cattle
B. suis found in pigs and occasionally in
goat
Other animal including horse, camel,
eland and wild rodents
21. Routes of infection
Mosquitoes helps in transfer Brucella
from animal to human
Also by ingesting unpastuerized milk,
meat or milk products, enter damaged
skin or eyes, inhaled in airborne particles
or aerosols and close contact with
secretions.
22. Microscopic observation
Non-motile
Gram negative
Coccobacili
Show bipolar staining
Rarely found in direct smear from
uncultured specimen
On Gram stain they appear as dense
clumps of Gram-negative coccobacilli
and are exceedingly difficult to see.
23. Culture characteristics
Mostly cultured from blood of high fever patient(Brucellosis)
Isolation is extremely rare in chronic brucellosis
In all blood culture, they need carbon dioxide
Blood culture should be kept in 4 – 6 weeks before result as no
organisms isolated
To reduce the risk of contamination, use the diphasic medium
such as Castaneda or tryptic soy broth or agar
Brucellae are aerobic with enriched of carbon dioxide
24. Biochemical tests Serology
tests
Urease and Possess two
hydrogen sulphide antigens called A
production and M
All brucella strains Famous test serum:
are catalase positive Rapid slide
agglutination test
Tube agglutination
titration test
25. Serology test
Itis crucial to be able to differentiate
Brucella from Salmonella which could
also be isolated from blood cultures and
are Gram-negative. Testing for urease
would successfully accomplish the task;
as it is positive for the Brucella and
negative for the Salmonella.