6. Morphology and General
Characteristics
Are facultative anaerobes
Gram-negative, non-sporing, rod shaped bacteria
If motile, motility is by peritrichous flagella(Except
Shigella & Klebsiella)
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
7. Morphology and Physiology
Short gram-negative rods.
Facultative anaerobes.
Grow readily and rapidly on
simple media.
K. pneumoniae
Klebsiella spp. have large capsule
(form large and very mucoid colonies);
those of Enterobacter have smaller
capsule; the others produce diffusible
slime layers (form circular, convex and
smooth colonies).
8. ENTEROBACTERIACEAE PHYSIOLOGY
Glucose is fermented with strong acid
formation and often gas
Reduce nitrates to nitrite
Do not liquify alginate
Oxidase negative
Basis for speciation within a family
- differences in carbohydrate they ferment
- variations in end-product production
- variation in substrate utilization
12. CULTURAL CHARACTERISTICS
On non differential or nonselective media
blood agar or infusion agar
- no species distinction
- appear as moist, smooth, gray colonies
Selective media -To isolate Shigella and
salmonella from fecal matter
Differential media – selectively inhibit
gram-positive organisms and to separate
enterics in broad categories
13. Modes of Infection
• Contaminated food and water (Salmonella spp.,
Shigella spp., Yersinia enterocolitica, Escherichia coli
O157:H7)
• Endogenous (urinary tract infection, primary bacterial
peritonitis, abdominal abscess)
• Abnormal host colonization (nosocomial pneumonia)
• Transfer between debilitated patients
• Insect (flea) vector (unique for Yersinia pestis)
17. Antigenic StructureAntigenic Structure
– Most are motile byMost are motile by peritrichous flagellaperitrichous flagella ----HH
antigens.antigens.
– Capsule –Capsule – KK antigen (antigen ( ViVi for Salmonella).for Salmonella).
– Cell envelope (wall)Cell envelope (wall)
– LPS (endotoxin) –LPS (endotoxin) –
OO antigen.antigen.
– various outervarious outer
membrane proteins.membrane proteins.
– PiliPili - various antigen- various antigen
types, some encodedtypes, some encoded by plasmidsby plasmids
18. Pathogenesis and Immunity
Common virulence factors
Type III secretion systems: possessed by some Enterobacteriaceae
pathogens, e.g., E. coli, Yersinia, Salmonella, and Shigella; facilitate
transport of bacterial virulence factors directly into host cells.
Endotoxin (Lipid A of LPS)
Capsule
Antigenic phase variation
Acquisition of growth factors (e.g. Fe)
Resistance to serum killing
Antimicrobial resistance
20. Escherichia coliEscherichia coli
Toxins: two types of enterotoxin; Shiga-type toxin;
Enteroaggregative ST-like toxin; Hemolysins;
Endotoxin
Virulence factors that protect the bacteria from host
defenses: Capsule/Iron capturing ability (enterochelin)
21. E. coli
May be hemolytic on CBA – more common in pathogenic
strains
KEY tests for the normal strain:
TSI is A/A + gas
LIA K/K
Urea –
Indole +
Citrate –
Motility +
There is an inactive biotype that is anaerogenic, lactose –,
and nonmotile.
22. EnteropathogenicEnteropathogenic E. coliE. coli
fever
infant diarrhea
vomiting
nausea
non-bloody stools
Destruction of surface microvilli loose attachment mediated by
bundle forming pili (Bfp);
Stimulation of intracellular calcium level;
rearrangement of intracellular actin,
EnterotoxigenicEnterotoxigenic E. coliE. coli
A watery diarrhea, nausea, abdominal cramps and low-grade
fever for 1-5 days.
Travellers diarrhea and diarrhea in children in developing
countries
Transmission is via contaminated food or water.
23. E.coli-E.coli-Enteroinvasive (EIEC)Enteroinvasive (EIEC)
The organism attaches to the intestinal mucosa via pili
Outer membrane proteins are involved in direct penetration,
invasion of the intestinal cells, and destruction of the intestinal
mucosa.
There is lateral movement of the organism from one cell to
adjacent cells.
Symptoms- fever,severe abdominal cramps, malaise, and watery
diarrhea followed by scanty stools containing blood, mucous,& pus.
resembles shigellosis
E.coli-E.coli-c. Enteropathogenic (EPEC)c. Enteropathogenic (EPEC)
Malaise and low grade fever diarrhea, vomiting, nausea, non-
bloody stools
Bundle forming pili are involved in attachment to the intestinal
mucosa.
This leads to changes in signal transduction in the cells,
effacement of the microvilli, and to intimate attachment via a non-
fimbrial adhesion called intimin.
This is a problem mainly in hospitalized infants and in day care
centers.
25. EnteroaggregativeEnteroaggregative E. coliE. coli
a cause of persistent, watery diarrhea with
vomiting and dehydration in infants.
That is autoagglutination in a ‘stacked brick’
arrangement.
the bacteria adheres to the intestinal mucosa
and elaborates enterotoxins
(enteroaggregative heat-stable toxin, EAST).
The result is mucosal damage, secretion of
large amounts of mucus, and a secretory
diarrhea.
27. Shigella species
Shigella
Contains four species that differ antigenically and, to a lesser
extent, biochemically.
S. dysenteriae (Group A)
S. flexneri (Group B)
S. boydii (Group C)
S. sonnei (Group D)
bacillary dysentery, shigellosis, bloody feces, intestinal pain, pus
Biochemistry
TSI K/A with NO gas
LIA K/A
Urea –
Motility -
All ferment mannitol except S. dysenteriae
S. sonnei may show delayed lactose fermentation
28. Shiga toxinShiga toxin
1. Chromosomally encoded
2. Neurotoxic
3. Enterotoxic
4. Cytotoxic
EnterotoxicityEnterotoxicity can make the disease clinically
appear as a diarrheadiarrhea.
The toxin inhibits protein synthesistoxin inhibits protein synthesis (acting on the
60S ribosome and lysing 28S rRNA).
29. Clinical significanceClinical significance
man only "reservoir"man only "reservoir"
mostly young childrenmostly young children
– fecal to oral contactfecal to oral contact
– children to adultschildren to adults
transmitted by adult food handlerstransmitted by adult food handlers
– unwashed handsunwashed hands
30. Diagnosis of Shigella infectionDiagnosis of Shigella infection
Specimen: stool.
Culture and Identification
Quick immunological methods:
1. Immunofluorescent “ball” test;
2. Coagglutination.
32. Only a few types that are commonly associated
with characteristic human diseases -
1.1. S. enteritidisS. enteritidis
2.2. S. cholerae-suisS. cholerae-suis
3.3. S. typhiS. typhi
SalmonellaSalmonella
several syndromes including gastroenteritis, enteric
(typhoid) fever or septicemia
33. Salmonella
Biochemistry
TSI K/A + gas and H2S: S. typhi produces only a small
amount of H2S and no gas , and S. paratyphi A produces
no H2S
LIA K/K with H2S with S. paratyphi A giving K/A results
Urea –
Motility +
Citrate +/-
Indole -
Virulence factors
Endotoxin – may play a role in intracellular survival
Capsule (for S. typhi and some strains of S. paratyphi)
Adhesions – both fimbrial and non-fimbrial
34. Salmonella typhiSalmonella typhi
• The organism is transmitted from:
1. a human reservoir1. a human reservoir
2. in the water supply (if poor sanitary conditions)2. in the water supply (if poor sanitary conditions)
3. in contaminated food3. in contaminated food
The antigenic structures of salmonellae used in serologic typingThe antigenic structures of salmonellae used in serologic typing
35. Virulence factorsVirulence factors
Endotoxin – may play a role in intracellular survival
Capsule (for S. typhi and some strains of S. paratyphi)
Adhesions – both fimbrial and non-fimbrial
Type III secretion systems and effector molecules – 2 different systems may be
found:
– One type is involved in promoting entry into intestinal epithelial cells
– The other type is involved in the ability of Salmonella to survive inside macrophages
Outer membrane proteins - involved in the ability of Salmonella to survive
inside macrophages
Flagella – help bacteria to move through intestinal mucous
Enterotoxin - may be involved in gastroenteritis
Iron capturing ability
37. DDiagnosisiagnosis
A. SpecimensA. Specimens
a) Enteric fever: blood, bone marrow, stool,a) Enteric fever: blood, bone marrow, stool,
urine.urine.
b) Food poisoning: stool, vomitus, suspected food.b) Food poisoning: stool, vomitus, suspected food.
c) Septicemia: blood.c) Septicemia: blood.
B. Culture and identificationB. Culture and identification
C. Widal testC. Widal test
38. Klebsiella
NF of GI tract, but potential pathogen in other areas
TSI A/A + gas
LIA K/K
Urea +
Citrate +
MR-, VP+
Motility -
Has both O and
K antigens
39. Klebsiella
Virulence factors
Capsule
Adhesions
Iron capturing ability
Clinical significance
Causes pneumonia, mostly in immunocompromised hosts.
Permanent lung damage is a frequent occurrence (rare in
other types of bacterial pneumonia)
A major cause of nosocomial
infections such as septicemia and
meningitis
K.Pneumoniae On BA
K.Pneumoniae on BA and MAC
40. ProteusProteus
General characteristics: “swarming” phenomenonGeneral characteristics: “swarming” phenomenon
on nonselective agaron nonselective agar (P.vulgaris; P.mirabilis and(P.vulgaris; P.mirabilis and
P.myxofaciens)P.myxofaciens)
P.vulgaris strains (OX-19, OX-K, OX-2)haveP.vulgaris strains (OX-19, OX-K, OX-2)have
common antigen with Rickettsia (Weil-Felix test).common antigen with Rickettsia (Weil-Felix test).
urinary tract infections; food poisoningurinary tract infections; food poisoning..
41. Proteus spp.
Some enteric bacteria are motile.
Klebsiella species are not motile,
while Proteus species move very
actively by means of peritrichous
flagella, resulting in "swarming"
on solid medium.
Some strains of E. coli produce
hemolysis on blood plates.
44. Serratia
A free-living saprophyte
TSI A/A or K/A; +/- gas (does not ferment lactose)
LIA usually K/K
Citrate +
Motility +
Urea +/-
Has been found in RT and UT infections
Is resistant to many antimicrobics
45. Special Features:
Used in the differentiation of
genera and species. e.g. E.
coli (+) from Klebsiella (-)
Positive tes
e.g. E. coli
Negative test
e.g. Klebsiella
IIndole testndole test
Positive
Klebsiella,
Enterobacter
Negative
E. coli
Citrate Utilization Test
Urease Test
Positive
test
Negative test
46. MMR/R/VVP testP test
Results
Methyl Red test Voges-Proskauer test
Red: Positive MR (E. coli)
ellow or orange: Negative MR (Klebsiella)
Pink: Positive VP (Klebsiella)
No pink: Negative VP (E. coli)
49. Oxidase TestOxidase Test
PositiveNegative
Pseudomonas
Enterobacteriacea
e
Nitrate test: +ve further
reduction to N2
Growth on cetrimide agar:
Pale colonies with green
pigmentation
MacConkey’s agar & TSI
Lactose fermenter
Pink colonies on MacConkey
& acidic butt and slant on TSI
colorless colonies on MacConkey
& acidic butt alkaline slant onTSI
Lactose non-fermenter
IMViC test
& EMB
IMViC
++ - -
& black colonies
with metalic
shines on EMB
E.coli
IMViC
- - ++
Klebsiella
No H2S production
(no blacking in TSI)
H2S production
(blacking in TSI)
Shigella
Urease production
+ve
Proteus
-ve
SS agar
colorless colonies with black centers
Salmonella
O/F test: O+
/F-
Motility
Not motile
Motile
