Enterobacteriaceae I: Enterobacteriaceae I: Opportunistic PathogensOpportunistic Pathogens

Enterobacteriaceae I: Enterobacteriaceae I: Opportunistic PathogensOpportunistic Pathogens

Enterobacteriaceae• Opportunistic Pathogen:

– Escherichia– Klebsiella– Proteus– Enterobacter– Serratia– Edwardsiella– Citrobacter

• Intestinal Pathogen:– Salmonella– Shigella– Yersinia

Enterobacteriaceae: General Characteristics• 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– Escherichia– Klebsiella– Enterobacter– Salmonella

Sites of Infection• Gastrointestinal (GI) Tract

– Salmonella– Shigella– Yersinia– Escherichia

• Urinary Tract (UT)– Escherichia– Proteus– Klebsiella– Providencia

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)

• 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

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 “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

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, ±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

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 • 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• NF of GI tract• TSI = A/A• LIA = K/K • IMViC = (--++)• Clinical significance:

– Nosocomial infections– Bacteremia in burn patients

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

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

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

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

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 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!