3. Commonly
present in large intestine
Non sporing , Non Acid fast, Gram –
bacilli.
A complex family of organisms,
Some are non pathogenic
A few are highly Pathogenic,
Some commensals turn out to be
pathogenic. as in UTI after
catheterization.
Dr.T.V.Rao MD
2/20/2014
4. • Are facultative anaerobes
• If motile, motility is by peritrichous flagella
• Many are normal inhabitants of the
intestinal tract of man and other animals
• Some are enteric pathogens and others are
urinary or respiratory tract pathogens
• Differentiation is based on biochemical
reactions and differences in antigenic
structure
5. • 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.
Most of this media is selective by
incorporation of dyes and bile salts that
inhibit G+ organisms and may suppress the
growth of nonpathogenic species of
Enterobacteriaceae.
Many are differential on the basis of whether
or not the organisms ferment lactose and/or
produce H2S.
6. All
•
•
•
•
Enterobacteriaceae
Gram-negative rods
Ferment glucose with acid production
Reduce nitrates into nitrites
Oxidase negative
Facultative
anaerobic
Motile except Shigella and Klebsiella
Non-capsulated except Klebsiella
Non-fastidious
Grow on bile containing media (MacConkey
agar)
Dr.T.V.Rao MD 2/20/2014
7. All
•
•
•
•
Enterobacteriaceae
Gram-negative rods
Ferment glucose with acid production
Reduce nitrates into nitrites
Oxidase negative
Facultative
anaerobic
Motile except Shigella and Klebsiella
Non-capsulated except Klebsiella
Non-fastidious
Grow on bile containing media (MacConkey
agar)
Dr.T.V.Rao MD 2/20/2014
8. Gram
negative bacilli or coccobacilli
Non-spore forming
Colony morphology on BAP or CA of
little value, as they look the same,
except for Klebsiella
Selective and differential media are
used for initial colony evaluation
(ex. MacConkey, HE, XLD agars)
9. Some
•
•
•
•
Enterobacteriaceae are true pathogens
Salmonella spp.
Shigella spp.
Yersinia spp.
Certain strains of E. coli (ETEC, EPEC, EIEC, EHEC)
Most
members of the Enterobacteriaceae are
opportunistic or cause secondary infections of
wounds, the urinary and respiratory tracts, and
the circulatory system e.g. E. coli.
Enterobacteriaceae divided into TWO main
groups according to action on LACTOSE
• Lactose Fermenters (LF)
E. coli, Citrobacter, Klebsiella, Enterobacter
• Lactose Non-Fermenters (LNF)
Salmonella, Shigella, Proteus, Yersinia
Dr.T.V.Rao MD
2/20/2014
10. Enterobacteriaceae
Lactose fermenters
E. coli, Citrobacter,
Klebsiella, Enterobacter
Non-lactose fermenter
Salmonell, Shigella
Proteus, Yersinia
There are several selective and differential media used to
isolate distinguishes between LF & LNF
The most important media are:
MacConkey agar
Eosin Methylene Blue (EMB) agar
Salmonella Shigella (SS) agar
Dr.T.V.Rao MD
In addition to Triple Sugar 2/20/2014
Iron (TSI) agar
11. Oxidase Test
Negative
Positive
Enterobacteriaceae
Pseudomonas
MacConkey’s agar
& TSI
O/F test: O+/F Nitrate test: +ve further
reduction to N2
Pink colonies on MacConkey colorless colonies on MacConkey
& acidic butt and slant on TSI & acidic butt alkaline slant onTSI
Growth on cetrimide agar:
Lactose non-fermenter
Pale colonies with green
pigmentation
Lactose fermenter
IMViC test
& EMB
IMViC
++ - & black colonies
with metalic
shines on EMB
E.coli
No H2S production
(no blacking in TSI)
IMViC
- - ++
Shigella
Urease production
+ve
Motility
Not motile
H2S production
(blacking in TSI)
-ve
SS agar
Motile
colorless colonies with black centers
Proteus
Dr.T.V.Rao MD 2/20/2014
Salmonella
12. MacConkey agar is selective & differential medium for Enterobacteriaceae
MacConkey Agar
Contains
Bile salts
Crystal violet
Inhibit growth of G+ve bacteria
Lactose
Cause of differential
Cause of selectivity
Lactose feremnters
Pink coloniesDr.T.V.Rao MD
Neutral red
pH indicator
Acidic: Pink
Lactose non feremnters
colorless colonies
2/20/2014
16. Growth of Enterobacteriaceae on SS agar
Both are lactose fermenters
Both Salmonella sp. & Proteus product H2S
Pseudomonas colonies are nearly colorless
18. Principle
Acidic pathway
Glucose
Or
Acety methyl carbinol
(ACETOIN)
Mixed acids
pH less than 4.4
Barrit’s A
Barrit;s B
Methyl Red
indicator
Red color
Neutral pathway
VP positive
MR positive
Klebsiella
Dr.T.V.Rao MD 2/20/2014
E. coli
Pink color
19. Indole,
Methyl Red, VogesProsakaur, Citrate (IMViC) Tests:
• The following four tests comprise a
series of important determinations that
are collectively called the IMViC series of
reactions
• The IMViC series of reactions allows for
the differentiation of the various
members of Enterobacteriaceae.
Dr.T.V.Rao MD
2/20/2014
20. Principle
Certain microorganisms can metabolize
tryptophan by tryptophanase
The enzymatic degradation leads to the
formation of pyruvic acid, indole and ammonia
The presence of indole is detected by addition
of Kovac's reagent.
Tryptophane
amino acids
Tryptophanase
Indole + Pyurvic acid + NH3
Kovac’s Reagent
Red color Dr.T.V.Rao MD organic layer`
in upper 2/20/2014
21. Method:
Inoculate tryptone water with the
tested microorganism
Incubate at 37 C for 24 hours
After incubation interval, add 1 ml
Kovacs reagent, shake the tube
gently and read immediately
Dr.T.V.Rao MD
2/20/2014
22. Negative test
e.g. Klebsiella
Result:
A bright pink color in the top
layer indicates the presence
of indole
The absence of color means
that indole was not produced
i.e. indole is negative
Special Features:
Used in the differentiation of
genera and species. e.g. E. coli
(+) from Klebsiella (-).
Dr.T.V.Rao MD
2/20/2014
Positive test
e.g. E. coli
23.
Inoculate the tested organism into One tube of MRVP broth
Incubate the tubes at 37 C for 24 hours
AFTER INCUBATION: Pour 1/3 of the suspension into a clean
nonsterile tube:
Run the MR test in the tube with 2/3, and the VP test in the open tube with
1/3.
For methyl red: Add 6-8 drops of methyl red reagent.
For Voges-Proskauer: Add 12 drops of Barritt's A (-naphthol),
mix, 4 drops of Barritt's B (40% KOH), mix
Let sit, undisturbed, for at least 1hour
Dr.T.V.Rao MD
2/20/2014
24. Results
Voges-Proskauer test
Methyl Red test
Pink: Positive VP (Klebsiella)
Red: Positive MR (E. coli)
Yellow or orange: Negative MR (Klebsiella)
No pink: Negative VP (E. coli)
Dr.T.V.Rao MD
2/20/2014
25. Principle:
Citrate
Citrate Utilization Test
Pyruvate
Na2CO3
CO2 + Na + H2O
Alkaline,↑pH
Simmone’s Citrate media
Contains Citrate as a sole of C source
Bromothymol blue
Positive test
Blue colour
Positive test: Klebsiella, Enterobacter, Citrobacter
Negative test: E. coli
Dr.T.V.Rao MD
2/20/2014
26. Method
Streak a Simmon's Citrate agar slant with
the organism
Incubate at 37 C for 24 hours.
Dr.T.V.Rao MD
2/20/2014
27. Result
Examine
for growth (+)
Growth on the medium
is accompanied by a
rise in pH to change the
medium from its initial
green color to deep
blue
Positive
Klebsiella, Enterobacter 2/20/2014
Dr.T.V.Rao MD
Negative
E. coli
28. Principle
Urea
Urea agar contains urea and phenol red
Urease is an enzyme that catalyzes the conversion of
urea to CO2 and NH3
Ammonia combines with water to produce ammonium
hydroxide, a strong base which ↑ pH of the medium.
↑ in the pH causes phenol red r to turn a deep pink.
This is indicative of a positive reaction for urease
Urease
H2O
CO2 + NH3
NH4 OH
↑ in pH
Phenol Red
Method
Streak a urea agar tube with the organism
incubate at 37 C for 24 h
Dr.T.V.Rao MD
2/20/2014
Pink
Positive test
29. Result
If color of medium turns
from yellow to pink
indicates positive test.
Proteus give positive
reaction after 4 h while
Kelebsiella and
Enterobacter gave
positive results after 24 h
Positive test
Dr.T.V.Rao MD
2/20/2014
Negative test
30. TSI contains
•
Three different types of sugars
Lactose (10 part)
•
Glucose (1 part)
Sucrose (10 part)
Phenol red (acidic: Yellow)
TSI dispensed in tubes with equal butt & slant
Principle
•
To determine the ability of an organism to attack a specific
carbohydrate incorporated into a basal growth medium, with or
without the production of gas, along with the determination of
possible hydrogen sulphide production.
Dr.T.V.Rao MD
2/20/2014
31. Method:
•
Inoculate TSI medium with an
organism by inoculating needle by
stabbing the butt and streaking the
slant
• Incubate at 37 C for 24 hours
Dr.T.V.Rao MD
2/20/2014
32. Reaction on TSI
Butt color
Slant color
Yellow
Red
Yellow
Red
Yellow
Yellow
Red
Red
H2 S
Negative
Positive
black in butt
Negative
Negative
Result
s Result
Example
A/Alk/(Glucose fermented)
LNF
e.g. Shigella
A/Alk/+
(Glucose fermented with H2S)
LNF
e.g. Salmonella &
Proteus
A/A/(three sugars are fermented)
LF
e.g. E. coli, Klebsiella,
Enterobacter
Alk/Alk/(No action on sugars)
Non fermenter e.g.
Pseudomonas