Chapter 24 - Microbial Diseases of the Digestive System

Gastrointestinal (GI) tract organs

mouth, pharynx, esophagus, stomach, small intestine, large intestine

Accessory organs of the digestive system

teeth, tongue, salivary glands, liver, gallbladder, pancreas

GALT (gut associated lymphoid tissue)

-immune response within GI tract

-Peyer's patches (lymphoid nodules) in lining of small intestines

-Lymph nodes

Normal Microbiota of the digestive system

Millions of bacteria per ml of saliva

Few in stomach (due to HCl)

Large numbers in large intestine (anaerobes and facultative anaerobes)

100 billion bacteria per gram of feces

Paneth cells

Phagocytic cells that secrete defensin enzymes that kill bacteria

Dental plaque

Biofilms involved in the formation of dental caries

Streptococcus mutans

Causes dental caries; gram-positive coccus; converts sucrose to lactic acid and produces dextran that forms plaque

Cariogenic bacteria

S. mutans, streptococci, filamentous Actinomyces

Dental Caries (Tooth Decay)

Starts with decay in enamel that then becomes advanced decay

Penetrates enamel into dentin

Decay reaches pulp

Can advance to soft tissues and cause abscess

Correlated with sugary diet that increases lactic acid production

Gingivitis

Inflammation/infection of the gums

Caused by streptococci, actinomycetes, and anaerobic gram-negatives

Periodontitis

Inflammatory disease of the bone and supporting tissues of the teeth

Caused by Porphyromonas

Acute necrotizing ulcerative gingivitis (trench mouth)

Infection producing ulcers in the mucous membranes of the mouth and throat

Caused by Prevotella intermedia

Staphylococcal food poisoning

Staphylococcal enterotoxicosis caused by S. aureus enterotoxin type A; coagulates plasma, heat stable, causes nausea, vomiting, diarrhea

Temperature abuse

When a food is either left in the temperature danger zone for an extended period of time, or does not reach its safe internal temperature; S. aureus outgrows most bacteria, especially in high osmotic pressure and temperature; common in creamy or salty foods

Shigellosis (Bacillary Dysentery)

Caused by the genus Shigella (facultatively anaerobic; gram-negative); produces Shiga toxin that damages tissue leading to bacillary dysentery: inflammation of intestines, fever, diarrhea, nausea, cramps, vomiting

Small infectious dose

Attaches to M cells, invades, and spreads to other cells and bloodstream

Treated with fluoroquinolones and oral rehydration

Dysentery

infection of the intestines resulting in severe diarrhea with the presence of blood and mucus in the feces.

Salmonellosis (Salmonella Gastroenteritis)

Salmonella enterica

Gram-negative, facultative anaerobe, nonendospore-forming rods

Normal inhabitant of the human intestinal tract

2000 serotypes

Invades intestinal mucosa and multiplies

Passes through M cells and enters the lymphatics

Replicates in macrophages

Salmonellosis symptoms

Incubation of 12 to 36 hours; fever, nausea, pain and cramps, diarrhea

Salmonellosis - risk factors

Consumption of undercooked chicken and eggs; bacteria survive in egg albumin; can cross-contaminate vegetables

Salmonellosis diagnosis and treatment

Diagnosis: Stool sample (microscopy and culture) or PCR

Treatment: oral rehydration therapy

Typhoid fever cause

Salmonella serotype Typhi (S. typhi); spread fecal-oral route; bacteria multiply in phagocytes and spread through blood

Typhoid fever symptoms

High fever, headache, intestinal wall ulceration; 1-3% become chronic carriers (gallbladder)

Typhoid fever treatment

Ceftrioxone, azithromycin

Cholera cause

Vibrio cholerae: gram-negative curved rod with polar flagellum; lives in salty water; produces cholera toxin that causes host cells to secrete electrolytes and water

Cholera symptoms

After drinking contaminated water:

-High volume watery diarrhea (up to 1 Liter per hour)

-Rice water stool

-Dehydration that can lead to shock, collapse, organ failure, and death

-No fever

Cholera treatment

IV fluid replacement

Noncholera vibrios

Vibrio parahaemolyticus: found in saltwater estuaries; common cause of gastroenteritis

Outbreaks associated with raw oysters and crustaceans

Require early antibiotic therapy

Enteropathogenic E. coli (EPEC)

Diarrhea in developing countries

Cause the host cells to form pedestals where the bacteria attach

Enteroinvasive E. coli (EIEC)

-diarrhea with pus

-similar to shigella

Enteroaggregative E. coli (EAEC)

Produce an enterotoxin causing watery diarrhea; only found in humans

Enterohemorrhagic E. coli (EHEC)

Produces Shiga-like toxin that is released upon the cell's lysis

Most outbreaks are O157:H7

Cattle are the main reservoir; also water and veg

Causes hemorrhagic colitis and hemolytic uremic syndrome

Diagnosed by the inability to ferment sorbitol and pulsed-field gel electrophoresis

Treated with IV rehydration and electrolytes

Hemorrhagic colitis

Abdominal cramps and bloody diarrhea, without fever, attributed to infection by a strain of E. coli.

Hemolytic uremic syndrome

A condition in which hemolytic anemia and thrombocytopenia cause acute renal failure and possibly death

Traveler's Diarrhea

Causes: most commonly ETEC, second EAEC; also Salmonella, Shigella, Campylobacter

Treatment: oral rehydration, bismuth and other OTC antidiarrheals

Campylobacteriosis

Caused by C. jejuni (gram-negative spiral curved microaerophilic); leading cause of foodborne disease in US (poultry, cattle feces, milk)

Symptoms: fever, cramping, abdominal pain, diarrhea, dysentery; rarely (1/1000) leads to Guillain-Barre syndrome

Helicobacter Peptic Ulcer Disease

Caused by H. pylori - grows in stomach by producing urease that converts urea to ammonia; disrupts stomach mucosa causing inflammation

Treatment: antimicrobials and bismuth subsalicylate

Diagnosis: biopsy, culture, urea breath test

Yersinia gastroenteritis

Caused by Y. enterocolitica and Y. pseudotuberculosis (gram-negative); transmitted by undercooked meat and pork; grows at 4°C

Symptoms: diarrhea, fever, headache, abdominal pain (can be misdiagnosed as appendicitis)

Treatment: antibiotics and oral rehydration

Clostridium perfringens gastroentertis

Caused by C. perfringens (gram-positive endospore forming obligate anaerobic rod)

Associated with animal intestines (low oxygen)

Symptoms: mild diarrhea 8-12 hours after ingestion (can also cause gas gangrene)

Treatment: oral rehydration

Clostridium difficile

Gram-positive endospore-forming anaerobic rod found as normal microbiota of the intestine.

Precipitated by therapy with broad-spectrum antibiotics (nosocomial)

Exotoxins cause ulceration and perforation of intestinal wall leading to life-threatening colitis

Bacillus cereus

Large, gram-positive endospore forming rod common in soil and vegetation; often transmitted in rice dishes and spores survive heating

Toxins cause diarrhea, nausea and vomiting

usually self-limiting

Mumps

Virus spread through saliva, causing inflammation of parotid gland 16-18 days post-exposure; virus multiplies in respiratory tract and reaches salivary glands through blood; may cause orchitis, meningitis, ovary inflammation, pancreatitis

Prevention: MMR vaccine

Hepatitis A virus (HAV)

A nonenveloped, single stranded RNA virus

Spread through fecal-oral route and multiplies in GI tract epithelium

Diagnosed via IgM antibodies

HAV symptoms

Anorexia, malaise, nausea, diarrhea; can lead to jaundice and dark urine

Symptoms 2-21 days, low mortality

HAV treatment and prevention

Treatment: immunoglobulins

Prevention: inactivated vaccine

Hepatitis B virus (HBV)

enveloped dsDNA virus

Transmission is through the blood and body fluids

Dane particles

Complete HBV virions

Spherical and filamentous particles

HBV particles lacking DNA but containing surface antigens

HBV prevention and treatment

Prevention: vaccine from genetically modified yeast

Treatment: no specific treatment, may require liver transplant

Acute HBV

Often subclinical, similar symptoms to HAV; gradual recovery

Fulminant hepatitis

An uncommon, rapidly progressing form that can quickly lead to liver failure, hepatic encephalopathy, or death within 3 weeks

Chronic HBV

10% of infected patients; can lead to liver cirrhosis or cancer; presence of HBeAg indicates high viral replication rate; treatment: interferons and nucleoside analogs

Hepatitis C virus (HCV)

Enveloped ssRNA; transmission via blood transfusions or other blood/bodily fluid contact

Destroys liver and uses antigenic variation to evade immune system; higher mortality than AIDS in US; 85% of cases become chronic and 25% develop cirrhosis of liver

HCV treatment and prevention

Treatment: protease and polymerase inhibitors, interferon, ribavirin

Prevention: no vaccine

Hepatitis D virus (HDV)

Acute (coinfection with HBV) and chronic (superinfection) forms; prevented via HBV vaccine

Hepatitis E virus (HEV)

a virus that is transmitted through the oral-fecal route and causes a form of hepatitis similar to HAV; endemic in areas with poor sanitation

Rotavirus

-Common in children; low mortality

-2 to 3 day incubation; low-grade fever, diarrhea, vomiting

-Prevented with a live oral vaccine

Norovirus

-Caliciviruses

-Fecal-oral transmission

-Low infectious dose

-18 to 48 hour incubation; diarrhea and vomiting

-Detected with PCR and EIA tests

Mycotoxins

toxins produced by fungi

Can cause blood diseases, nervous system disorders, kidney and liver damage, and cancer

Ergot poisoning

Mycotoxins produced by Claviceps purpurea

Occurs in grains

Restricts blood flow (gangrene) and causes hallucinations

Aflatoxin poisoning

Mycotoxins produced by Aspergillus flavus

Likely to be found on peanuts

Causes liver cirrhosis and liver cancer

Giardiasis

Caused by Giardia intestinalis (aka G. lamblia)

Flagellated protozoan; cysts in feces and water and trophozoites in host that attach to intestinal wall

Giardiasis symptoms

Prolonged diarrhea, malaise, weight loss, flatulence, cramps

Hydrogen sulfide detected in the breath or stools

Giardiasis diagnosis and treatment

Diagnosed with a string test, ELISA, or FA test

Treated with metronidazole and nitazoxanide

Cryptosporidiosis

Caused by Cryptosporidium parvum and C. hominis

Ingested oocysts release sporozoites

Invade the intestinal epithelium

Transmitted through drinking water

Resistant to chlorination

Cryptosporidiosis symptoms

Cholera-like diarrhea for 10 to 14 days

Cryptosporidiosis diagnosis and treatment

Diagnosed with an FA test or immunoassay tests

Treatment with nitazoxanide

Cyclospora

Caused by Cyclospora cayetanensis; fecal-oral route; oocysts ingested

Symptoms: days or weeks of watery diarrhea

Diagnosis: no satisfactory tests

Treatment: trimethoprim and sulfamethoxazole

Amebic dysentery

Caused by Entamoeba histolytica; cysts survive stomach acid and trophozoites multiply in intestinal wall

Amebic dysentery symptoms

Perforation of intestinal wall can cause abscesses and liver infection; blood and mucus in feces

Amebic dysentery diagnosis and treatment

Diagnosed via serological EIA tests

Treatment with metronidazole

Beef tapeworm

Taenia saginata

Pork tapeworm

Taenia solium

Fish tapeworm

Diphyllobothrium latum

Taeniasis

adult tapeworm infects the intestine

Cysticercosis

Infection with the larval stage by ingesting eggs

Ophthalmic cysticercosis

Larvae of tapeworm lodge in the eye

Neurocysticercosis

Tapeworm larvae develop in the central nervous system

Tapeworm life cycle

-Eggs are excreted in the feces and ingested by

animals.

-Eggs hatch into a larval cysticercus that lodges in the muscle of the animal.

-Human ingests undercooked meat containing cysticerci, which develop into adult tapeworms in the intestine.

Tapeworm diagnosis and treatment

Diagnosis: eggs or segments in feces

Treatment: praziquantel and niclosamide

Hydatid Disease

Caused by the tapeworm Echinococcus granulosus

Eggs are ingested and migrate to the liver, lungs, or brain where they develop a hydatid cyst that can hold up to 15 liters of fluid

Cyst rupture can cause anaphylactic shock

Diagnosis with serological tests, X rays, CT, and MRI

Treatment with surgical removal or albendazole

Pinworms

Caused by Enterobius vermicularis (a small nematode) that lays eggs around the anus, causing local itching

Treatment with pyrantel pamoate and mebendazole

Hookworms

Caused by the nematodes Necator americanus and Ancylostoma duodenale

Attaches to the intestinal wall and feeds on blood and tissue

Anemia, lethargic behavior, and craving for peculiar foods (pica)

Carried from human feces in soil that contact bare skin

Treatment with mebendazole

Ascariasis

Caused by the nematode Ascaris lumbricoides

30% of the worldwide population is infected with few or no symptoms

Eggs shed in the feces and are ingested by another person

Hatch into larvae and pass into the bloodstream and lungs

Larvae migrate to the throat and are swallowed

Larvae develop into adult worms in the intestinal tract and emerge from the anus, mouth, or nose

Treatment with mebendazole or albendazole

Whipworm

Trichuris trichiura; 30-50mm long; ingested eggs invade intestinal glands; eggs hatch and grow on intestinal surfaces; adult burrows into mucosa and feeds on cells and blood

Whipworm symptoms

Symptoms: Anemia, malnutrition, retarded growth

Treatment: mebendazole or albendazole

Trichinellosis

Caused by Trichinella spiralis

Encysted larvae are ingested from undercooked pork and other meats

Digestion removes the cyst wall and the worm matures into an adult

Adults produce larvae in the intestines that invade tissues and form new cysts

Trichinellosis symptoms and treatment

Fever, eye swelling, gastrointestinal upset

Treatment with albendazole or mebendazole