Chapter 16: Enteric Bacteria-Secretory Diarrhea

Diarrhea

The excessive discharge of water fluid from the bowel.

*It is rather a symptom of a disease than a disease itself.

Organisms that cause intestinal disease

• Bacteria

• Viruses

• Parasites

Coliforms

Secretory (watery) diarrhea

= loss of electrolytes and fluids from the small intestinal tract.

Bloody diarrhea (dysentery)

= local tissue damage or inflammation of the intestinal tract

What is the most common cause of diarrhea ?

Viral gastroenteritis

What is the second most common cause of diarrhea?

Bacterial gastroenteritis

*More severe

How many children die from diarrhea annually?

More than 5 million children

What are the enteric bacterial pathogens for Vibrionaceae?

• Vibrio cholerae

• Campylobacter jejuni

What are the enteric bacterial pathogens for Enterobacteriaceae?

• Pathogenic E. coli

• Shigella flexneri (EIEC)

• Salmonella typhimurium

• Yersinia enterocolitica

What are the main characteristics for Vibrio cholerae?

• Gram-negative curve rod

• Motile

• Facultative anaerobes

• Single polar flagellum

• Positive oxidase reaction

V. cholerae

• Associated with algae and marine invertebrates in

external environments

• Causes cholera

• Serotypes on basis of O antigen: O1 and O139 strains;

O1 are more virulent (Classic, El Tor biovar)

What does the V. cholerae attaches to?

The surface of a freshwater alga

How is cholera acquired?

Acquired by ingestion of contaminated water or seafood

What are the clinical symptoms for cholera?

• Watery diarrhea, vomiting

• Start 2-3 days after ingestion of the bacteria

• Followed by dehydration, renal failure

• “Rice water” stool

What is the mortality rate of cholera?

• 60% in untreated patients

• Less than 1 % in treated patients

What are the virulence factors ?

• Polar flagellum provides motility

• Tcp pili

• Cholera toxin (A-B type cholera)

• Other potential toxins

• Capsule (present in 0139 strin but not in 01)

Antibiotics resistance

Probably not a problem because antibiotics are rarely used

Prevention & treatment

• Oral rehydration therapy (salt and glucose in

• water)

• Antibiotics used occasionally (to reduce toxic

• production and rapidly eliminate the pathogen)

• Vaccine provides limited protection; other vaccines are in development

• Main prevention measurement: good hygiene

Who identified E.coli?

• Theodor Escherich

• 1885

What are the characteristics of E. coli?

• Gram-negative rod

• Facultative anaerobes

• Oxidase negative

• Motile

What is the reservoir for E. coli?

Human and animal

Enterotoxigenic E. coli (ETEC)

• Travelers diarrhea (watery diarrhea)

• Worldwide, adults and children

Enteropathogenic (EPEC)

• Watery diarrhea

• Infants <1y of age

Enteroaggregative (EAggEC)

• Watery diarrhea, persistent diarrhea

• infants <6 month of age, AIDS patients

Enteroinvasive (EIEC)

• Bloody diarrhea

• Uncommon, often foodborne

Enterohemorrhagic (EHEC)

• Bloody diarrhea

• Hemorrhagic colitis

• Hemolytic-uremic syndrome

• Western nations

ETEC

• Causes Traveler’s diarrhea; mostly in developing countries (650 million cases/year)

• Pathogen usually contaminates water and fresh vegetable

• Produces 2 heat-labile enterotoxins (LT-I, LT-II), 2 heat-stable toxins, and Type 1 adhesins; LT-I is similar to cholera toxin

When does Traveler’s diarrhea develop?

• Develops after 1-2 days incubation time

• Persists for 3-4 days

What are the main symptoms for traveler’s diarrhea?

• Watery diarrhea

• Abdominal cramps

EPEC

• Causes diarrhea in infants and small children

• EPEC was the first E. coli associated with diarrheal diseases

• Pathogen does not produce toxins

• Adhesins: intimin, pili (BfpA)

• Type III secretion system-Tir receptor

EPEC-mediated diarrhea

• Characterized by microvilli destruction in the small intestine

• Leads to malabsorption (inability to absorb food)

EAggEC

• Causes persistent diarrhea in children and adults in both developed and developing countries

• Bacteria aggregative and form a biofilm on the epithelium of small intestine

• Produce an enterotoxin and hemolysins

EAggEC-mediated diarrhea

Symptoms:

• Persistent watery diarrhea with vomiting

• Low grade fever

• Dehydration