Enterobacteriaceae I:
Opportunistic Pathogens
Enterobacteriaceae
• Opportunistic Pathogen:
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Escherichia
Klebsiella
Proteus
Enterobacter
Serratia
Edwardsiella
Citrobacter
• Intestinal Pathogen:
– Salmonella
– Shigella
– Yersinia
Enterobacteriaceae:
General Characteristics
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Gram (-) rod
Catalase(+)
Oxidase(–)
Ferment glucose
Reduce nitrate
Motile by peritrichous flagella
(except Klebsiella, Shigella, Yersinia)
General Characteristics
• Facultative anaerobes
• Normal inhabitants of intestinal tract
humans, other animals
• Enteric pathogen
• Some are urinary, respiratory tract
pathogen
• Differentiate by biochemical test and
antigenic structure
Lab Culture Media
• CBA:
– Colonies large, dull gray
– ± hemolysis
• Selective Media:
– Dye, bile salt inhibit G(+) MO
– EMB, Mac - selective for Enterobacteriaceae:
– SS, HE, XLD - highly selective for enteric
pathogens, inhibit NF
• Differential:
– Lactose fermentation
– H2S production
Serologic ID: Major Antigens
• O - Somatic LPS antigen
– Major cell wall antigen
– Heat stable polysaccharide
– Component of endotoxin
• H - Flagellar antigen
– Protein
– Heat labile
• K - Capsule antigen
– Polysaccharide
– Heat labile
– Vi (virulence) antigen in Salmonella
typhi
• I.D. pathogenic E. coli O157:H7
strain
Biochemical Tests
• TSI (Triple Sugar Iron Agar) –
glucose, lactose, sucrose, H2S
indicator
• LIA (Lysine Iron Agar)
– lysine deaminase – aerobic, slant
– Lysine decarboxylase – anaerobic, butt
– H2S indicator – anaerobic, butt
• Motility – soft (0.4%) agar
• 1% Glucose broth (MR-VP) – acid or
neutral metabolic end product
• Citrate – use as sole C source
• Indole – tryptone product
• Urea – hydrolysis by urease
• PAD – phenylalanine deaminase
Virulence Factors
• Endotoxin – Gram(-) cell wall:
– LPS release upon cell death
– Symtoms by Lipid A - fever, leukopenia,
cytokine action
– Immune and inflammatory response
– Vasodilation, capillary leakage
– Disseminated Intravascular Coagulation (DIC);
blood coagulation, decreased circulation
– Hypotension, shock, death
• Capsule – prevent phagocytosis, resist
serum killing by C’
Virulence Factors: Enterotoxin
• Movement of water & ions from
tissue to bowel resulting in watery
diarrhea
• Two types of enterotoxin:
– Heat-stable (ST) – activate cGMP
– Heat-labile (LT) – activate cAMP
• Shiga toxin – inhibit protein
synthesis:
– Enterohemorrhagic strains of E. coli
(EHEC)
– Cytotoxic, enterotoxic, neurotoxic
– Diarrhea, ulceration of G.I. tract
• Enteroaggregative toxin - produced
by E. coli (EAEC), causes watery
diarrhea
Virulence Factors
• Hemolysin – cytotoxin to RBC’s, leukocytes
• Enterochelin - capture iron
• Outer membrane proteins – attachment, initiate
endocytosis for cell invasion
• Adhesions – pili, fimbriae, non-fimbrial factors
for host cell (GI, urinary, CNS) attachment;
antibodies to adhesions may protect from
colonization
Sites of Infection
• Central Nervous System (CNS)
– Escherichia
• Lower Respiratory Tract (LRT)
– Klebsiella
– Enterobacter
– Escherichia
• Bloodstream
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Escherichia
Klebsiella
Enterobacter
Salmonella
Sites of Infection
• Gastrointestinal (GI) Tract
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Salmonella
Shigella
Yersinia
Escherichia
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Escherichia
Proteus
Klebsiella
Providencia
• Urinary Tract (UT)
Escherichia coli
• Normal inhabitant G.I. tract, present in
water, vegetation
• Various forms of gastroenteritis
• Major cause of:
– Urinary tract infection
– Neonatal meningitis
– Septicemia
• Transmission:
– Endogenous spread in susceptible patient
– Ingest contaminated food or water
– Nosocomial infection
Escherichia coli: Biochemical
Test ID
• May be hemolytic on CBA, more
common in pathogenic strains
• Key Test:
– TSI = A/A + gas
– LIA = K/K
– IMViC = (++--)
Escherichia coli: Infections
• Neonatal Meningitis leading cause, along with
Strep Gp. B
• Septicemia - GU
infection or own GI NF,
high mortality
• Urinary Tract Infection –
leading cause, by own NF:
– acute cystitis (bladder
infection)
– pyelonephritis (kidney
infection)
Escherichia coli: Gastroenteritis
• ETEC (Enterotoxigenic E.
coli) – infant diarrhea,
Traveler’s diarrhea
• EPEC (Enteropathogenic E.
coli ) – infant diarrhea
• EAEC (Enteroaggregative E.
coli) – chronic diarrhea in
children
• EIEC (Enteroinvasive E. coli)
– dysentery in children and
adults
• EHEC (Enterohemorrhagic
E. coli) – hemorrhagic colitis,
hemolytic uremic syndrome
ETEC (Enterotoxigenic E. coli)
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Traveler’s diarrhea
Diarrhea of children in developing countries
These strains rare in U.S.
MO attaches to intestinal mucosa, liberates
enterotoxin
• Disease characterized:
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Watery diarrhea
Nausea
Abdominal cramps
Low-grade fever for 1-5 days
• Transmission via contaminated food or water
EPEC (Enteropathogenic E. coli )
• Bundle forming pili
attachment intestinal
mucosa
• Effacement of
microvilli, exact
pathogenesis unclear
• Diarrhea, large amounts
mucous, no blood or pus,
vomiting, malaise, low
grade fever
• Outbreaks in nurseries
and day care centers
EAEC (Enteroaggregative E. coli)
• Bacteria associated
autoagglutinins cause
aggregation in “stackedbrick” arrangement at cell
surface of mucus biofilm
• Process mediated by bundleforming pili (BFP)
• MO attach and liberate
cytotoxin
• Symptoms include watery
diarrhea, vomiting,
occasional abdominal pain,
dehydration >14 days
• Chronic diarrhea and growth
retardation of children in
developing countries
EIEC (Enteroinvasive E. coli)
• MO attaches to intestinal mucosa; direct
penetration, invasion of intestinal cells,
destruction of intestinal mucosa
• Lateral movement of MO from one cell to
adjacent cells
• Symptoms include fever, severe abdominal
cramps, malaise, watery diarrhea, followed by
scanty stools containing blood, mucus,
leukocytes and pus
• Person to person transmission via fecal-oral
route
EHEC (Enterohemorrhagic E. coli)
• Attach to intestinal mucosa, liberates Shiga
toxin, also termed Verotoxin (cytopathic to
Vero monkey kidney cell culture)
• Watery diarrhea, progress to bloody diarrhea
without pus, crampy abdominal pain, ±lowgrade fever
• May progress to hemolytic uremic syndrome
(HUS):
– Anemia, kidney failure
– Highly fatal - infants (<5 yrs.), elderly
• By E. coli O157:H7 serotype
• Epidemics traced to consumption of
undercooked beef, unpasteurized juice
Summary: E.coli Gastroenteritis
E. coli: Treatment and
Control
• Susceptible to variety of antibiotics
• Drug resistant strains increasing, need
susceptibility testing
• Hospital infection control important
• Education to improve hygiene, hand
washing
Klebsiella: ID
• NF of GI tract, potential pathogen in
other sites
• TSI = A/A + gas
• LIA = K/K
• Urea (+)
• Citrate (+)
• MR(-), VP(+)
• Motility (–)
Klebsiella: Infections
• Virulence factors:
– Capsule
– Adhesions
– Iron capturing ability
• Clinical significance:
– Pneumonia - mostly immunocompromised hosts;
permanent lung damage frequent occurrence
(rare in other bacterial pneumonia)
– Major cause of nosocomial infection –
septicemia, meningitis
Proteus: ID
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NF of GI tract
Motile, with swarming on CBA
TSI = K/A + H2S (similar to Salmonella)
LIA = R/A (lysine deamination)
PAD = (+) (phenylalanine deamination)
Urea = strongly (+) for Proteus
Indole – only P. mirabilis is (-)
Proteus: Infections
• Virulence factors
– Urease – ammonia produced may damage
epithelial cells of UT
• Clinical Significance
– UT infections; also pneumonia,
septicemia, wound infections
Enterobacter: ID & Infections
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NF of GI tract
TSI = A/A
LIA = K/K
IMViC = (--++)
Clinical significance:
– Nosocomial infections
– Bacteremia in burn patients
Serratia: ID & Infections
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Free-living saprophyte
TSI = K/A
LIA = K/K
Citrate (+)
Urea (±)
Has been found in RT and UT infections
Resistant to many antibiotics
Edwardsiella: ID & Infections
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TSI = K/A + gas, H2S
LIA = K/K +H2S
Urea(–)
Citrate(–)
Indole(+)
Clinical significance – causes GI
disease in tropical and subtropical
countries
Citrobacter: ID & Infections
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TSI = K/A or A/A both + gas, H2S
LIA = K/A + H2S
Citrate (+)
Urea usually (+)
Opportunistic pathogen causing
urinary tract or respiratory tract
infections; occasionally wound
infections, osteomyelitis,
endocarditis, meningitis
Lab: Enterobacteriaceae
I Group Unknowns
TSI
• Escherichia
A/A
• Shigella
K/A
• Enterobacter A/A
• Klebsiella
A/A
LIA
K/K
K/A
K/K
K/K
Class Assignment
• Textbook Reading: Chapter 19
Enterobacteriaceae
• Key Terms
• Learning Assessment Questions
Case Study 3 Enterobacteriaceae
• A 25-year-old previously healthy woman
came to the emergency room for the
evaluation of bloody diarrhea and diffuse
abdominal pain of 24 hours’ duration.
• She complained of nausea and had vomited
twice.
• She reported no history of inflammatory
bowel disease, previous diarrhea, or
contact with other people with diarrhea.
Case Study 3
• The symptoms began 24 hours after she
had eaten an undercooked hamburger at a
local fast food restaurant.
• Rectal examination revealed watery stool
with gross blood.
• Sigmoidoscopy showed diffuse mucosal
erythema and petechiae with a modest
exudation but no ulceration or
pseudomembranes.
Case Study 3 - Questions
• 1. Name four genera of
Enterobacteriaceae that can cause
gastrointestinal disease. Name two genera
that can cause hemolytic colitis.
• 2. What virulence factor mediates this
disease?
• 3. Name the five groups of E. coli that can
cause gastroenteritis. What is
characteristic of each group of organisms?
• 4. Differentiate between disease caused
by S. typhi and that caused by S. sonnei.
Lecture Exam I
Thursday, Feb. 2, 2012
• Introduction thru Enterobacteriaceae
• Lecture, Reading (Chap. 14, 15, 17, 19),
Key Terms, Learning assessment
Questions, Case Study 1,2,3
• Exam Format:
– Multiple Choice
– Terms
– True/False Statements
– Short Essay
• Review, Review, Review!