Download GENERAL CHARACTERISTICS OF PROTEUS

Practical Microbiology/
Enterobacteriaceae family
The Enterobacteriaceae are a large
family of Gram - negative
bacteria that includes, along with many harmless symbionts , many of the
more familiar pathogens, such as Salmonella , Escherichia coli , Klebsiella ,
Shigella and Yersinia pestis. Other disease-causing bacteria in this family
include Proteus , Enterobacter, Serratia, and Citrobacter.
Characteristics
Members of the Enterobacteriaceae are rod-shaped , and are typically
1-5 μm in length. They appear as small grey colonies on blood agar. Like
other proteobacteria, enterobacteria have Gram-negative stains , and they
are facultative anaerobes , fermenting sugars to produce lactic acid and
various other end products. Most also reduce nitrate to nitrite, Most have
many flagella used to move about, but a few genera are nonmotile. They are
not spore-forming. Catalase reactions ( + )
Many members of this family are a normal part of the gut flora found in
the intestines of humans and other animals, while others are found in water
or soil , or are parasites on a variety of different animals and
plants. Escherichia coli is one of the most important model organisms , and
its genetics and biochemistry have been closely studied.
This family is divided into two groups depending on the fermentation of
lactose
1- Lactose Fermentation (the colony appear rose or pink on MacConkey
agar) such as Esherichia coli , Klebsiella , Citrobacter.
2- Non Lactose Fermentation ( the colony appear pile or colorless on
MacConkey agar ) such as proteus , Shigella , salmonella
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CHARACTERISTICS OF ESCHERICHIA COLI
1-Grows with and without air
.2-Grows between 45ºF and 114ºF
.3-Survives freezing temperatures •
4-Many strains are harmless ,Source of pathogenic strains is infected
animals and people..
5-Found in raw milk, raw meat, nonchlorinated water ,contaminated
fruits and vegetables
6-Vegetative cells multiply and produce toxins in intestinal tract to
cause illness .
7-Vegetative cells killed by cooking / pasteurization •
Bacterial Characteristics
may or Escherichia coli is a gram negative, non-spore forming rod. It
may not be mobile. (Some rods are flagellated and some
are not.) The organism is a facultative anaerobe and ferments simple
sugars such as glucose to form lactic, acetic, and formic
acid
.
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Table 1 Differentiating characters of main genera of Enterobacteriaceae
Acid
Genus
from
Lactose
Gas from
glucose
Motility
Urease
Citrate
Voges –
Utlized
Proskauer
Escherchia
+
+
+
-
-
-
Shigella
-
-
-
-
-
-
Citrobacter
+
+
+
d
+
-
Salmonella
-
+
+
-
+
-
Enterobacter
+
+
+
d
+
+
Klebsiella
+
+
-
+
+
+
Serratia
d
d
+
-
+
+
Proteus
-
+
+
+
d
-
+ = positive reaction
Escherichia
coli :
- = negative reaction
is
d= variable reactions
a Gram-negative, facultatively
anaerobic,
rod-shaped bacterium of the genus Escherichia that is commonly found in
the lower intestine of warm-blooded organisms (endotherms )
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Characterization of Escherichia coli
It is gram negative facultative bacteria non-spore forming bacilli and most
strains (about 80%) are motile and few strains are capsulated , fermentive
lactose with production gas within 48 hours at 37 C º on MacConkey medium
, E.coli colonies are smooth , glassy and translucent , rose –pink in color .
On blood agar the colonies of some strains are surrounded by zone of
hemolysis , that it is motile , forms gas from glucose , ferments lactose
produce indol (+) , gives a positive methyl-red reaction and VP(-) and dose
not
utilize
citrate(-)
,
grow
in
KCN
,
liquefy
gelatin.
GENERAL CHARACTERISTICS OF PROTEUS
Gram-negative rods that are distinguished from other members of the
Enterobacteriaceae by their ability to produce the enzyme phenylalanine
deaminase
Produce the enzyme urease(+), which cleave urea(+) to form NH3 and
CO2
Certain species are very motile and produce striking a swarming effect on
blood agar, characterized by expanding rings (waves) of organisms over the
surface of the agar.(Swarming Phenomenon)
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LABORATORY DIAGNOSIS
1-Culture .
A . On MacConkey agar produce non-lactose fermenter (colorless) colony
b . On blood agar produce characteristic Swarming phenomena which
considered as diagnostic feature for Proteus however, can cause
misdiagnosis for other bacteria as it can cover other colonies and
cannot obtain pure culture
2-Staining by Gram stain : Gram –ve rods .
3-P. vulagaris and p. mirabilis produce H2S which blacken the butt of TSI
agar
4- P. mirabilis is indole negative, while others are indole positive .
5-Ferment glucose producing acid and gas .
6-Urea agar (urease test) = Pink (+)
7-Citerate (-)
8-MR(+) , VP(-)
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GENERAL CHARACTERISTICS OF Klebsiella pneumoniae
1- Normal inhabitant in digestive & respiratory system of animal
&humane.
2- Lactose Fermenters
3-thick-short rod rounded end.
4-Its dimension (1-2 ×0.5-0.8)
5- arrangement single or diplobacilli
6-Non motile
7-have fimbriae
8-produce capsule (thick from lipopolysaccharide)
9- Easily grow on normal culture media
10- Mucous textures
11- Citrate Utilization (+) ,VP(+),urease (+) / indol(-), MR(-) ,
Gelatin Utilization(-)
12-sensitive to heat, you die during 30 minute on 55Cº
GENERAL CHARACTERISTICS OF Salmonella
1- its dimensions (2-4 ×0.4-0.6 µ) , long or short (coccobacilli )
2-Non spore-forming
3-Aerobic or facultative anaerobic
4-Selective media
1-selenite broth
2-tetrathionate broth
3-salmonella-shigella agar
4-brilliant green agar
5-Xylose lysine deoxycholate agar (XLD agar)
5-indole(-) ,VP(-) , Urase (-) / H2S(+) ,Citrate (+) decarboxylase (+)
6-sensitive to heat, you die during 20 minute on 60Cº
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Enterobacter
is a genus of common Gram-negative, facultatively anaerobic, rod-shaped,
non-spore-forming bacteria of the family Enterobacteriaceae. Several strains
of these bacteria are pathogenic and cause opportunistic infections in
immunocompromised
(usually hospitalized) hosts and in those who are
on mechanical ventilation. The urinary and respiratory tracts are the most
common sites of infection. The genus Enterobacter is a member of
the coliform group of bacteria. It does not belong to the fecal coliforms (or
thermotolerant coliforms) group of bacteria, unlike Escherichia coli, because
it is incapable of growth at 44.5 °C in the presence of bile salts. Some of
them showed quorum sensing properties as reported before
Two clinically important species from this genus are E. aerogenes and E.
cloacae.
The genus Enterobacter ferments lactose with gas production during a 48hour incubation at 35-37 C° in the presence of bile salts and detergents. It is
oxidase
(-)
,
indole
(-)
,
urease
(V)
,
Citrate
Utlized(+), VP(+)
Citrobacter
genus of Gram negative coliform bacteria in the Enterobacteriaceae family.
The species C. amalonaticus, C. koseri, and C. freundii can use citrate as a
sole carbon source. Citrobacter species are differentiated by their ability to
convert tryptophan to indole (+), ferment lactose, and Urease (-)
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