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Enterobacteriaceae I: Enterobacteriaceae I: Opportunistic PathogensOpportunistic Pathogens
Enterobacteriaceae I: Enterobacteriaceae I: Opportunistic PathogensOpportunistic Pathogens
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Enterobacteriaceae• Opportunistic Pathogen:
– Escherichia– Klebsiella– Proteus– Enterobacter– Serratia– Edwardsiella– Citrobacter
• Intestinal Pathogen:– Salmonella– Shigella– Yersinia
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Enterobacteriaceae: General Characteristics• Gram (-) rod• Catalase(+)• Oxidase(–)• Ferment glucose• Reduce nitrate• Motile by peritrichous flagella (except
Klebsiella, Shigella, Yersinia)
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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
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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
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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
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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
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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’
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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
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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
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Sites of Infection• Central Nervous System (CNS)
– Escherichia• Lower Respiratory Tract (LRT)
– Klebsiella– Enterobacter– Escherichia
• Bloodstream– Escherichia– Klebsiella– Enterobacter– Salmonella
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Sites of Infection• Gastrointestinal (GI) Tract
– Salmonella– Shigella– Yersinia– Escherichia
• Urinary Tract (UT)– Escherichia– Proteus– Klebsiella– Providencia
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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
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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 = (++--)
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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)
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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
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ETEC (Enterotoxigenic E. coli)
• Traveler’s diarrhea• Diarrhea of children in developing countries• These strains rare in U.S.• MO attaches to intestinal mucosa, liberates enterotoxin• Disease characterized:
– Watery diarrhea– Nausea– Abdominal cramps– Low-grade fever for 1-5 days
• Transmission via contaminated food or water
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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
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EAEC (Enteroaggregative E. coli)
• Bacteria associated autoagglutinins cause aggregation in “stacked-brick” arrangement at cell surface of mucus biofilm
• Process mediated by bundle-forming 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
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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
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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, ±low-grade 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
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Summary: E.coli Gastroenteritis
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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
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Klebsiella: ID
• NF of GI tract, potential pathogen in other sites
• TSI = A/A + gas• LIA = K/K• Urea (+)• Citrate (+)• MR(-), VP(+)• Motility (–)
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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
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Proteus: ID • 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 (-)
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Proteus: Infections• Virulence factors
– Urease – ammonia produced may damage epithelial cells of UT
• Clinical Significance– UT infections; also pneumonia,
septicemia, wound infections
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Enterobacter: ID & Infections• NF of GI tract• TSI = A/A• LIA = K/K • IMViC = (--++)• Clinical significance:
– Nosocomial infections– Bacteremia in burn patients
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Serratia: ID & Infections• Free-living saprophyte• TSI = K/A• LIA = K/K• Citrate (+)• Urea (±)• Has been found in RT and UT infections• Resistant to many antibiotics
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Edwardsiella: ID & Infections• TSI = K/A + gas, H2S
• LIA = K/K +H2S
• Urea(–)• Citrate(–)• Indole(+)• Clinical significance – causes GI disease
in tropical and subtropical countries
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Citrobacter: ID & Infections • 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
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Lab: Enterobacteriaceae I
Group Unknowns TSI LIA• Escherichia A/A K/K• Shigella K/A K/A• Enterobacter A/A K/K• Klebsiella A/A K/K
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Class Assignment• Textbook Reading: Chapter 19
Enterobacteriaceae • Key Terms• Learning Assessment Questions
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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.
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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.
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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.
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Lecture Exam IThursday, 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!