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CHAPTER

Microbial Diseases of

the Digestive System

Chapter Outline

Structures of the Digestive System (pp. 710–711)

The Gastrointestinal Tract

The Accessory Digestive Organs

Microbiome of the Digestive System (p. 711)

Bacterial Diseases of the Digestive System (pp. 712–725)

Dental Caries, Gingivitis, and Periodontal Disease

Peptic Ulcer Disease

Viral Diseases of the Digestive System (pp. 725–732)

Oral Herpes

Mumps

Viral Gastroenteritis

Viral Hepatitis

Protozoan Diseases of the Intestinal Tract (pp. 732–737)

Giardiasis

Cryptosporidiosis

Amebiasis

Helminthic Infestations of the Intestinal Tract (pp. 737–741)

Tapeworm Infestations

Chapter Summary

Structures of the Digestive System (pp. 710–711)

Anatomists commonly divide the structures of the digestive system into two groups: those of the

gastrointestinal (GI) tract and the accessory digestive organs.

Instructor’s Manual for Microbiology with Diseases by Body System, 5e

The Gastrointestinal Tract

The GI tract is a long tube lined with mucous membrane and composed of the mouth, esopha-

gus, stomach, small intestine, large intestine, rectum, and anus. The peritoneum surrounds and

protects most organs of the GI tract. Food in the tract is moved through the tract by peristalsis.

The Accessory Digestive Organs

Accessory digestive organs include the tongue, teeth, liver, gallbladder, and pancreas. The teeth

and tongue are important in tearing, mashing, and mixing food into a bolus. The salivary glands

provide salivary amylase and lubrication for swallowing. The teeth tear (incisors and canines)

Microbiome of the Digestive System (p. 711)

The esophagus, stomach, and duodenum (the upper portion of the small intestine) are almost

free of microbes. The rest of the GI tract is colonized by a variety of microbiota.

Bacteria, fungi, and a few protozoa reside on the surfaces and in the pits and crevices of the oral

Bacterial Diseases of the Digestive System (pp. 712–725)

Bacterial digestive diseases are typically mild and self-limiting, but a few can be fatal, especial-

ly in infants, the elderly, and the immunocompromised.

Dental Caries, Gingivitis, and Periodontal Disease

Dental caries (tooth decay or cavities) is the second most common infection of humans. Strep-

tococcus mutans produces an insoluble, sticky, polysaccharide slime called dextran and forms

Chapter 23 Microbial Diseases of the Digestive System

the disease progresses. An extreme form of periodontal disease is known as acute necrotizing

ulcerative gingivitis (ANUG or trench mouth).The microbes responsible for dental caries and

gingivitis include Streptococcus mutans, species of Lactobacillus, and Porphyromonas gingi-

valis.

Diagnosis of caries and gingivitis is made primarily by observation of visible damage. Minor

caries are treated by removing the damaged area of the tooth and applying a filling. More seri-

Fluoridation of water is an effective public health measure to prevent dental disease.

Peptic Ulcer Disease

Peptic ulcers (peptic ulcers, duodenal ulcers) are erosions of the linings of either the

stomach or duodenum. Ulcers that pierce the stomach or intestine are perforations. The erosions

are mostly due to bacterial invasion. Abdominal pain, the major symptom, is caused by the inva-

sive action of Helicobacter pylori, a G(−) motile slightly helical bacterium with numerous viru-

lence factors. Among other virulence factors, H. pylori possesses a protein that inhibits acid

production by stomach cells, flagella that enable it to burrow through the mucus lining the stom-

Bacterial Gastroenteritis

Bacterial gastroenteritis (inflammation of the stomach or intestines) is caused by the presence

of bacteria. Manifestations typically include nausea, vomiting, diarrhea, loss of appetite, ab-

dominal pain, and cramps. In rare cases, kidney failure or anemia can occur. In a severe and

painful type of gastroenteritis known as dysentery, stools are loose, frequent, and contain mu-

cus and blood. Diagnosis is based on signs and symptoms; the causative agent can be identified

by nucleic acid test (xTAG Gastrointestinal Pathogen Panel, aTAG GPP) or culturing. Treat-

ment usually involves replacement of fluids and electrolytes. Antidiarrheal drugs may prolong

20%). Symptoms and the presence of the Shigella spp. in a stool sample are diagnostic. An-

timicrobial drugs such as ceftriaxone, are used to treat of severe cases, and a vaccine is under

development.

 Traveler’s diarrhea is the common name for bacterial gastroenteritis caused by infection

with Escherichia coli, a Gram-negative coliform that lives in the GI tract of humans and other

animals. E. coli strains are distinguished from one another on the basis of O, H, and K anti-

 Campylobacter diarrhea is caused by infection with Campylobacter jejuni, a Gram-negative

bacterium with polar flagella that possesses adhesins, cytotoxins, and endotoxin (lipid A). C.

 C. diff. (antimicrobial-associated) diarrhea is a severe form of diarrhea frequently seen in

hospitalized patients taking antimicrobial drugs. The most severe form is known as pseudo-

membranous colitis. The Gram-positive, endospore-forming, anaerobic bacillus Clostridium

difficile is a part of the normal microbiome of the large intestine in about 5% of adults and up

to 70% of newborn Americans. C. difficile overgrows in the colon when antimicrobial treat-

 Salmonellosis and typhoid fever are caused by infection with Salmonella enterica, a Gram-

negative bacillus that lives in the intestines of virtually all vertebrates and is eliminated in

their feces. Salmonella is not part of the normal microbiome of most humans, but some indi-

viduals can be asymptomatic carriers. Humans acquire the infection by consuming contami-

nated food or water. Chicken eggs are a major source of salmonellosis. Virulent serotypes of

 Cholera is caused by the Gram-negative bacillus Vibrio cholerae, which can survive in both

saltwater and freshwater environments. Some strains of V. cholerae produce a potent poison

Chapter 23 Microbial Diseases of the Digestive System

Bacterial Food Poisoning (Intoxications)

Food poisoning is a broad term used to refer to either consuming pathogens (gastroenteritis) or

their toxins (bacterial intoxications or toxifications). General symptoms of bacterial intoxication

Viral Diseases of the Digestive System (pp. 725–732)

Viral diseases of the digestive system include oral herpes, mumps, viral gastroenteritis, and viral

hepatitis.

Oral Herpes

Oral herpes is among the most common of the infections caused by the Herpesviridae family.

Its symptoms include painful, itchy, creeping fluid-filled lesions, called fever blisters or cold

sores, on the lips. Initial infections may be accompanied by malaise, fever, and muscle pain. Se-

vere infection extending into the oral cavity is called herpetic gingivostomatitis, and infection

affecting the pharynx is herpetic pharyngitis. Immunosuppressed individuals may develop her-

Mumps

Mumps is a viral infection of the large salivary glands on each side of the face. Effective im-

munization has made mumps nearly extinct in developed nations, but epidemics in the late win-

ter and early spring still occur in nations with inadequate immunization programs. Infection with

a genus of Rubulavirus, commonly known as the mumps virus, causes swelling of the large sali-

vary glands on the side of the face (parotitis), pain, fever, headache, and sore throat. Other or-

gans are occasionally infected. Treatment is supportive care and pain medication, but recovered

individuals have lifelong immunity.

Instructor’s Manual for Microbiology with Diseases by Body System, 5e

Viral Gastroenteritis

Although the general manifestations of viral gastroenteritis are the same as those of bacterial

gastroenteritis, viral forms are usually less severe than bacterial forms of the disease. Dehydra-

Viral Hepatitis

Hepatitis is inflammation of the liver produced by autoimmune disease, alcohol or drug abuse,

genetic disorders, or microbial infection. Three viruses are responsible for most cases of viral

hepatitis. Symptoms include jaundice, abdominal pain and distention, dark urine, light-colored

stools, loss of appetite, nausea, vomiting, fatigue, fever, and weight loss. Liver failure can occur

with chronic infection.

Five viruses that cause hepatitis include: Hepatovirus Hepatitis A virus (HAV), Or-

system is unable to clear the hepatitis C virus because of its high mutation rate.

Signs and symptoms provide preliminary diagnosis; serologic tests identify cause. Treatment

involves rest and reducing inflammation; there is no cure. Immunoglobulin given immediately

after exposure offers some protection. Alpha interferon and nucleotide analogs tenofovir in con-

Chapter 23 Microbial Diseases of the Digestive System

Protozoan Diseases of the Intestinal Tract (pp. 732–737)

Relatively few protozoa cause infection of the GI tract.

Giardiasis

Giardiasis is one of the more common water-borne GI diseases in the United States. A flagel-

lated diplomonad named Giardia intestinalis, a common resident of waterways throughout the

United States, causes giardiasis and forms protective cysts in which it can survive for months.

Cryptosporidiosis

Infection with the zoonotic apicomplexan Cryptosporidium parvum causes cryptosporidiosis, a

disease characterized by severe watery diarrhea several times a day lasting about two weeks.

Severe watery diarrhea several times a day lasting about two weeks is a common manifestation

Amebiasis

Amebas are protozoa with no defined shape that use pseudopodia to move and acquire food. In-

fection with Entamoeba histolytica, a motile trophozoite, can result in one of three forms of

amebiasis: Luminal amebiasis is generally asymptomatic; amebic dysentery is characterized by

severe diarrhea, colitis, appendicitis, ulceration of the intestinal mucosa, bloody stools, and/or

pain; invasive extraintestinal amebiasis causes potentially fatal necrotic lesions in the liver,

lungs, spleen, kidneys, or brain.

Infection typically begins with consumption of food or water containing cysts, or ingestion

Instructor’s Manual for Microbiology with Diseases by Body System, 5e

Helminthic Infestations of the Intestinal Tract (pp. 737–741)

Helminths can infest the GI tract as non–disease-causing parasites.

Tapeworm Infestations

Tapeworm is the common name for a cestode, which is a flat, segmented, parasitic helminth.

Tapeworm infestations are usually asymptomatic, and a person does not recognize the infesta-

tion until passing segments of the worm. Rarely, infestation is accompanied by nausea, ab-

dominal pain, weight loss, and diarrhea, and long worms occasionally block the intestines,

preventing normal bowel function. The common tapeworms of humans are Taenia saginata, the

Pinworm Infestations

Infestation with Enterobius vermicularis—commonly known as pinworm—commonly occurs

in children. Symptomatic infestation involves intense perianal itching, irritability, and sleep dis-

turbance due to itching, decreased appetite, and possibly weight loss. Enterobius is a nema-

tode—a long, thin, unsegmented cylindrical helminth tapering to points at each end. Male and

Anisakiasis

Anisakiasis is a disease resulting from infestation with parasitic nematodes, primarily Anisakis

simplex. Infestation may be asymptomatic, but some experience violent abdominal pain, nausea,