22.1. the Gastrointestinal Tract and Its Defenses

Chapter Outline

22.1. The Gastrointestinal Tract and Its Defenses

A. A long tube extending from mouth to anus.

B. Composed of eight main sections: the mouth, pharynx, esophagus, stomach, small intestine, large intestine, rectum, and anus

C. Four accessory organs: the salivary glands, liver, gallbladder, and pancreas

D. Often called the digestive tract or the enteric tract.
E. Defenses include:

1. Mucus

2. Secretory IgA

3. Peristalsis

4. Saliva contains lysozyme and lactoferrin

5. Stomach fluid is highly acidic

6. Bile is antimicrobial

7. Gut-associated lymphoid tissue (GALT)

8. Commensals in system provides microbial antagonism towards pathogens

22.2. Normal Biota of the Gastrointestinal Tract

A. Bacteria live on the teeth as well as the soft structures in the mouth

B. Pharynx has a variety of microorganisms

C. Stomach and esophagus are sparsely populated

D. The normal biota in the gut provides not only protection, but also aid in digestion

1. Anaerobes outnumber aerobes in gut

E. Accessory organs are free of microorganisms

22.3. Gastrointestinal Tract Diseases Caused by Microorganisms (Nonhelminthic)

A. Tooth and Gum Infections

1. Dental caries (tooth decay)

a. Causative agents

1. Streptococcus mutans

2. Streptococcus sobrinus
3. Scardovia wiggsiae

b. Pathogenesis and virulence factors

i. Produce sticky polymers of glucose

ii. Contribute to plaque biofilm

iii. Streptococci ferment the carbohydrates, producing acid

iv. Acid comes in contact with enamel of tooth, dissolving it

v. Nursing bottle caries

c. Transmission and epidemiology

d. Culture and diagnosis

e. Prevention and treatment

i. Dietary restriction of sucrose

ii. Regular brushing and flossing to remove plaque
iii. Removal of the tooth and restoration of its surface

B. Periodontal Disease

1. Periodontitis

a. Signs and symptoms

i. Gingivitis

ii. Periodontitis

b. Causative agent

i. Tannerella forsythus

ii. Actinobacillus actinomycetemcomitans

iii. Porphyromonas, Fusobacterium, and spirochete species

c. Pathogenesis and virulence factors

i. Calculus and plaque accumulating in gingival sulcus causes abrasions in gingival membrane

ii. Chronic trauma leads to pronounced inflammatory reaction

d. Transmission and epidemiology

e. Culture and diagnosis

f. Prevention and treatment

i. Regular brushing and flossing

ii. Dental hygiene

C. Necrotizing ulcerative gingivitis and periodontitis

1. Necrotizing ulcerative gingivitis (NUG)

2. Necrotizing ulcerative periodontitis (NUP)

3. Synergistic infections involving three pathogens:

a. Treponema vincentii

b. Prevotella intermedia

c. Fusobacterium species

D. Mumps

1. Signs and symptoms

2. Causative agent

a. Paramyxovirus

3. Pathogenesis and virulence factors

4. Transmission and epidemiology of mumps virus

5. Culture and diagnosis

6. Prevention and treatment

a. MMR Vaccine

E. Gastritis and gastric ulcers

1. Signs and symptoms

a. Gastritis: sharp or burning pain emanating from the abdomen

b. Gastric or duodenal ulcers (peptic ulcers) can be accompanied by bloody stools, vomiting, or both

2. Causative agent

a. Helicobacter pylori

3. Pathogenesis and virulence factors

a. Urease produced by H. pylori

4. Transmission and epidemiology

5. Culture and diagnosis

6. Prevention and treatment

a. Antibiotics

b. Acid suppressors

F. Acute diarrhea (with or without vomiting)

1. Salmonella

a. Signs and symptoms

i. Typhoid fever – typhi variant of Salmonella enterica

ii. Salmonellosis – other variants of S. enterica

b. Pathogenesis and virulence factors

i. Pathogenicity islands of genes

ii. Responsible for entry, adhesion, or invasion into the host

c. Transmission and epidemiology

i. Animal products

d. Prevention and treatment

i. Vaccine for poultry

ii. Fluid and electrolyte replacement in salmonellosis

iii. Antibiotics for typhoid fever

2. Shigella

a. Signs and symptoms

i. Shigellosis

ii. Dysentery (blood-containing diarrhea)

b. Pathogenesis and virulence factors

i. Enterotoxin

ii. Heat-labile exotoxin called shiga toxin

c. Transmission and epidemiology

i. Oral route

ii. Person-to-person contact

d. Prevention and treatment

3. Shiga-Toxin-Producing E. coli (STEC)

a. Shiga-toxin-producing E. coli, (STEC)

b. Signs and symptoms

i.Mild gastroenteritis with fever

ii. Hemolytic uremic syndrome (HUS)

c. Pathogenesis and virulence factors

i. Produces shiga toxin (shiga toxin-producing E. coli or STEC)

ii. Intimin – protein used for attachment to host cells

iii. Effacement in the gut – lesion formed by the bacteria – which results in the bloody diarrhea

d- Transmission
e- Culture and diagnosis

4. Other E. coli

a. Enterotoxigenic E. coli (Traveler’s diarrhea)

b. Enteroinvasive E. coli

c. Enteropathogenic E. coli

d. Enteroaggregative E. coli

5. Campylobacter

a. Campylobacteriosis

b. Most common bacterial cause of diarrhea in U.S.

i. Campylobacter jejuni

i. Guillain-Barré syndrome

6. Yersinia species

a. Yersinia enterocolitica and Y. pseudotuberculosis

b. High degree of abdominal pain (sometimes mistaken for appendicitis)

7. Clostridium difficile

a. Pseudomembranous colitis (antibiotic-associated colitis)

b. Seems to be precipitated by therapy with broad-spectrum antibiotics

8. Vibrio cholerae

a. Signs and symptoms

i. Rice-water stools

b. Pathogenesis and virulence factors

i. Enterotoxin called cholera toxin (CT)

ii. A-B toxin

c. Transmission and epidemiology

d. Culture and diagnosis

e. Prevention and treatment

i. Proper sewage treatment and water purification

ii. Key to therapy is replacement of water and electrolytes

9. Cryptosporidium

a. Intestinal water-borne protozoan

b. Gastroenteritis

10. Rotavirus

a. 1 million cases per year in the U.S.

b. Fecal-oral route

c. Babies 6-24 months are at greatest risk of death

11. Other viruses

a. Noroviruses, adenoviruses, and astroviruses

b. Fecal-oral transmission

c. Profuse, watery diarrhea

G. Acute diarrhea with vomiting (food poisoning)

1. Food poisoning caused by a preformed toxin

2. Staphylococcus aureus exotoxin

a. Associated with eating food that have been contaminated by handling and then left unrefrigerated for a few hours

b. Heating the food after toxin production may not prevent disease

3. Bacillus cereus exotoxin

a. Two exotoxins, one of which causes a diarrheal-type disease, the other of which causes an emetic (vomiting) disease

b. Most frequently linked to fried rice cooked and then kept warm for long periods of time

4. Clostridium perfringens exotoxin

a. Endospores

b. Toxin initiates acute abdominal pain, diarrhea, and nausea

H. Chronic diarrhea

1. Enteroaggregative E. coli (EAEC)

2. Cyclospora cayetanensis

a. Emerging freshwater protozoan pathogen

3. Giardia

a. Signs and symptoms

i. Diarrhea of long duration, abdominal pain, and flatulence

b. Pathogenesis and virulence factors

i. Giardia lamblia is a pathogenic flagellated protozoan

c. Transmission and epidemiology of giardiasis

i. Isolated from intestines of beavers, cattle, coyotes, cats, and human carriers

d. Culture and diagnosis

e. Prevention and treatment

i. Water treatment

ii. Therapy is metronidazole

4. Entamoeba histolytica

a. Signs and symptoms

i. Dysentery, abdominal pain, fever, diarrhea, and weight loss

b. Pathogenesis and virulence factors

c. Transmission and epidemiology of amoebiasis

i. Intestinal amoebiasis

ii. Freshwater protozoan

d. Culture and diagnosis

e. Prevention and treatment

i. Prevent through purification of water

ii. Metronidazole

I. Hepatitis

1. Necrosis of hepatocytes and a mononuclear response causing jaundice

2. Hepatitis A virus

a. Nonenveloped, single-stranded RNA enterovirus

b. Signs and symptoms

i. Often subclinical or vaguely flulike

ii. More overt cases include jaundice and swollen liver

iii. Darkened urine

iv. Virus is not oncogenic (does not result in cancer)

c. Pathogenesis and virulence factors

d. Transmission and epidemiology

i. Fecal-oral route

ii. Associated with deficient personal hygiene and inadequate public health measures

e. Culture and diagnosis

f. Prevention and treatment

i. An inactivated viral vaccine (Havrix)

3. Hepatitis B virus

a. Enveloped DNA virus in the family Hepadnaviridae

b. Signs and symptoms

i. Similar to symptoms in Hepatitis A infection with additional symptoms including fever, chills, malaise, anorexia, diarrhea, rash

ii. Some cases develop cirrhosis

iii. Malignancy: HBV is associated with hepatocellular carcinoma

c. Pathogenesis and virulence factors

d. Transmission and epidemiology

i. Blood

ii. Sex (bodily fluids)

e. Culture and diagnosis

f. Prevention and treatment

i. Recombinant HBV vaccine

ii. Passive immunization with HB immune globulin in exposed individuals

iii. Chemotherapy in chronic infections to manage disease; no cure

4. Hepatitis C virus

a. RNA virus in Flaviviridae family

b. Signs and symptoms

i. More likely to become chronic than hepatitis B disease

ii. Liver cancer due to HCV is a more common cause in U.S. than HBV

c. Pathogenesis and virulence factors

d. Transmission and epidemiology

i. Blood contact

ii. Vertical transmission

iii. Transmission through other body fluids is less common

e. Culture and diagnosis

f. Prevention and treatment

i. Treatment is interferon

22.4. Gastrointestinal Tract Diseases Caused by Helminths

1. Worm infection usually causes an increase in eosinophils, known as eosinophilia

2. General clinical considerations

3. Pathogenesis and virulence factors in general

a. Definitive host

b. Intermediate host

c. Accidental definitive host

4. Prevention and treatment in general

a. Minimize human contact with parasite

b. Interrrupt life cycle

c. Antihelminthic drugs, surgery

5. Intestinal distress as the primary symptom

a. Trichuris trichiura

i. Whipworm

b. Enterobius vermicularis

i. Pinworm

c. Tapeworms

i. Taenia solium

ii. Diphyllobothrium latum

iii. Hymenolepis species

6. Intestinal distress accompanied by migratory wymptoms

a. Ascaris lumbricoides

i. Intestinal roundworm

b. Necator americanus and Ancyclostoma duodenale

i. Hookworms

c. Strongyloides stercoralis

i. Threadworm

ii. AIDS patients

7. Liver and intestinal disease

a. Opisthorchis sinensis and Clonorchis sinensis

i. Chinese liver flukes

b. Fasciola hepatica

i. Sheep liver fluke

8. Muscle and neurological symptoms

a.Trichinosis

i. Trichinella spiralis

ii. Associated with eating undercooked pork (or wild meat) containing Trichinella cysts

b. Liver disease

i. Schistosomiasis

i. Schistosoma mansoni or S. japonicum

ii. Signs and symptoms

iii. Causative agents

i. Blood flukes

iv. Pathogenesis and virulence factors

i. Coats itself with host proteins

v. Transmission and epidemiology

vi. Culture and diagnosis

vii. Prevention and treatment