Citrobacter
Resembles Salmonella but are ONPG (+)
& LDC (-)
 Citrobacter species

 freundii (UTI, pneumonia, intraabdominal
abscess)
 diversus (neonatal meningitis)
 amalonaticus (extraintestinal infections)
H2S
Indole
KCN
C. freundii
+
+
S. diversus
+
-
Klebsiella
Klebsiella -Enterobacter-Serratia-Hafnia
K. pneumoniae
>Friedlander’s bacilli (encapsulated and
mucoid)
> (+) String test
Klebsiella aerogenes is associated with hospital
acquired infections of wounds and of the urinary
tract
K. rhinoschleromatis – rhinoscleromatis
(granulomatous disease of the nose and pharynx
with intense swelling and malformation of the entire
face and neck)
The patient's K. pneumoniae isolate
was string test positive (>5 mm
string length).
LABORATORY DIAGNOSES
Specimens: Depending on the site of infection, specimens
include urine, pus, sputum and infected tissue.
Morphology
Klebsiellae are Gram negative, non-motile, usually
capsulated rods.
Culture
Klebsiellae are aerobes and facultative anaerobes.
Blood agar: Klebsiellae produce large grey white usually
mucoid colonies.
 MacConkey agar and CLED medium: Most klebsiellae are
lactose-fermenting, producing mucoid pink colonies on MacConkey
agar and yellow mucoid colonies on CLED medium
 K. rhinoscleromatis is non-lactose fermenting.
 Biochemical tests
 Klebsiellae are indole negative, ornithine decarboxylase negative
and do not produce H2S.
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Klebsiella on Macconkey
medium show large mucoid
pink lactose fermenting
colony
Klebsiella on CLED medium show
yellow lactose fermenting colony
Enterobacter
-species: habitat: soil, water, dairy products
-normal flora of the gut of animals &
humans
-motile, ODC & ONPG (+)
Yellow Urease
pigment
V
-
+
-
+
+
ODC
ADH
LDC
+
+
+
-
+
E. cloacae 
E. aerogenes 
+
+
-
+
+
+
-
E. gergoviae 
E. sakazakii 
E. taylorae 
Enterobacter
Edwardsiella
Edwardsiella 
tarda (human pathogen – 
bacteremia and wound
infection)
hoshinae (snakes, birds and 
water)
ictaluri (enteric septicemia in 
fish)
Serratia
 opportunistic pathogens
 DNAse, lipase, gelatinase
○ S. marcescens
○ S. liquefaciens
○ S. rubidaea
○ S. oderifera
Serratia
Proteus

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Tow important species , P. mirabilis and P.
vulgaris
Morphology
Proteus is actively motile with peritricous flagella
, non capsulate, Gram negative pleomorphic
rods.
Rapid urease producers
Swarming, burned chocolate odor
Proteus with peritricous
flagella
Pathogenicity
P. mirabilis causes:
1- Urinary infections. in the elderly and
young males and often following
catheterization or cystoscopy..
2- Abdominal and wound infections
3- secondary invader of ulcers, burns and
damaged tissues.
4- Septicaemia
5- Meningitis and Chest infections.
Culture
aerobically, most Proteus cultures have a characteristic ‘fishy’
Odour and Swarming on the medium
MacConkey, CLED, XLD media: non-lactose
fermenting colonies after overnight incubation at 35–37 ºC
Swarming is prevented on MacConkey agar and XLD agar
because these media contain bile salts.
Swarming is inhibited on CLED agar because it
is electrolyte deficient
Biochemical tests
Do not ferment lactose.
Rapidly hydrolyze urea (within 4 hours), early screening test
in differentiating enteric pathogens, e.g. salmonellae and
shigellae from Proteus.
Phenylalanine deaminase (PDA), positive.
Indole negative (P. vulgaris is indole positive).
Proteus
Indole
ODC
Fermentation

Maltose

Xylose

Salicin
Chloramphenicol
P. mirabilis
+
+
S
P. vulgaris
+
+
+
+
R
Proteus
Indole
Maltose
Xylose
Salicin
Chloramphenicol
P. mirabilis
………
………
……..
……..
……..
P. vulgaris
…….
…….
…….
…….
……
Proteus

Proteus McConkey
Urease test
Swarming pehomenon
Swarming on Blood
agar
Morganella
Formerl known as Proteus
 M. morganii – only specie
 UTI’s and wound infections

Providencia
Providencia ( 4 species – P. alcalifaciens,
P. Rustigianii, P. rettgeri, P. stuartii)
P. rettgeri
P. stuartii

Urease
+

Citrate
+
+

Yersinia

11 species
 Y. pestis (plague) – bipolar staining (wayson)
 Agent of bubonic plague, pneumonic and septicemic plagues
○ Bubonic – bite of infected flea
○ Pneumonic
○ Prefered growth at 25 deg C
 Y. enterocolitica (acute enteritis – appendictis like)
○ Pig, cats and dogs
○ Cold enrichment
○ Motile at RT
 Y. pseudotuberculosis
○ Pathogen in animals (turkey, geese, doves, farm and
domestic animals)
Yersinia pestis
Safety pin appearance
Revision Question
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1- Characteristic of enterobacterceae all of the following
except :
a- Gram negative rod
b- Facultative anaerobic
c- Ferment glucose
d- Oxidase positive
2-Sworming is special characteristic of:
a. Pseudomonades
b- Proteus
c- E. coli
d- Klebsiella
3- Mucoid colony is special characteristic of:
a. Pseudomonades
b- Proteus
c- E. coli
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4- Bacteria which give green metallic sheen on EMB medium
is:
a. Pseudomonades
b- Proteus
c- E. coli
d- Klebsiella
5- Polysaccharide capsule present on which of the following
bacteria:
a. Pseudomonades
b- Proteus
c- Shigella
d- Klebsiella
6- Which of the following bacteria is urease positive :
a. Pseudomonades
b- Proteus
c- E. coli
d- Klebsiella
7- Which of the following bacteria is lactose fermenter:
a. Pseudomonades
b- Proteus

When we inoculate members of
enterobacterceae on MacConkey agar,
mention which organism grow producing
lactose fermentor colony and which grow
producing lactose fermentor colony
‫‪klebsiella and e.coli‬‬
‫الهم ال تجعل الدنيا اكبر همنا و ال‬
‫مبلغ علمنا‬