The document summarizes the Enterobacteriaceae family of bacteria. It describes their morphology as gram negative rods that are facultative anaerobes. It discusses their sub-grouping based on lactose fermentation and pigment production. It also outlines their culture characteristics, biochemical reactions, antigenic structures, and important genera like Escherichia, Klebsiella, Salmonella and Shigella. Selective media and differential tests help identify different members of the family.

1. 4.6 Enterobacteriaceae
Enteric Gram negative aerobes rods

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.

6. Klebsiella E.coli

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

9. E.coli
In nutrient agar In MacConkey agar

10. Klebsiella sp
In macconkey agar In blood agar

11. Salmonella sp
In ss agar In xld agar

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.

15. Antigenic Structure of
Enterobacteriaceae

16. Antigenic structure of
Enterobacteriacea

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

18. 4.7 BRUCELLA

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.