Chapter 23: Microbial Diseases of the Digestive System

Gastrointestinal tract or GI tract

The pathway from the mouth to the anus. Most organs are protected by the peritoneum. Also, digest food, absorb nutrients and water into the blood and eliminates wastes.

Accessory digestive organs

Involved in grinding food or providing digestive secretions.

What are the components of the gastrointestinal tract?

• Mouth

• Esophagus

• Stomach

• Small intestine

• Large intestine

• Rectum/anus

What are the accessory digestive organs?

• Tongue/Teeth

• Salivary glands

• Liver

• Gallbladder

• Pancreas

Esophagus, Stomach, and Duodenum

Regions are almost free of microbes. Peristalsis and rapid transport of food help prevent microbial colonization.

Tongue, Teeth, Jejunum, Ileum, Colon and Rectum

Viridans’s streptococci are most prevalent in this region.

The Microbiota here are microbial antagonists and mucous membrane prevents entry of microbes into the bloodstream.

Lower small intestine and the colon.

Dental Caries

Causative agent: streptococcus mutants

Classification: Low G+C Gram positive, viridian streptococci

Signs/Symptoms: appears as holes or pits in the teeth. Tartar

Pathogenesis: secrete dextran and has fimbriae allows biofilm formation.

Epidemiology: experienced by most adults. Diets high in sucrose increase risk of decay.

Diagnosis: visual inspection

Treatment: filling cavities if caught early.

Prevention: good oral hygiene.

Periodontal Disease

Causative agent: porphyromonas gingvalis

Classification: Gram negative bacillus, phylum bacteroidetes

Signs/Symptoms: gums are swollen, tender, bright red, and bleeding

Pathogenesis: secretes proteases that break down gingival tissue.

Epidemiology: experienced by most adults. Diets high in sucrose increase risk of decay.

Diagnosis: inspection of gums

Treatment: scaling and use of antibacterial rinses

Prevention: good oral hygiene

Campylobacter Diarrhea

Causative agent: campylobacter jejuni

Classification: gram negative, epsilonproteobacteria

Signs/Symptoms: bloody diarrhea, lesions, inflammation

Pathogenesis: virulence factors: adhesions, cytotoxins, endotoxins (lipid A)

Epidemiology: responsible for more cases of diarrhea. CDC : 1 million cases each year are infected.

Diagnosis: based on signs/symptoms, presence of bacterium in stool.

Treatment: most cases resolve without treatment

Prevention: proper hygiene after handling of raw poultry.

Antimicrobial-Associated Diarrhea

Causative agent: Clostridium difficile

Classification: Low G+C Gram positive bacillus, produce endospores

Signs/Symptoms: diarrhea and pseudo membrane colitis (yellow lesions)

Pathogenesis: antimicrobial use facilitates overgrowth. Remains in colon and don’t move into blood. Two toxins: A & B

Epidemiology: any antimicrobial can trigger disease. Byproduct of modern medicine.

Diagnosis: presence of toxins in stool or colonoscopy

Treatment: metronidazole and vancomycin, do not treat with anti diarrhea drugs.

Prevention: avoid unnecessary use of antimicrobials, personal hygiene including staff.

Bacterial Food Poisoning

Causative agent: staphylococcus aureus

Classification: Low G+C Gram Positive

Signs/Symptoms: nausea, vomiting, diarrhea, cramping, fever, loss of appetite.

Pathogenesis: S. Aureus produces 5 enterotoxins (A through E)

Epidemiology: social functions, many cases go unreported

Diagnosis: based on signs and symptoms

Treatment: replacement of fluid and electrolytes

Prevention: proper hygiene and handling of foods.

Viral Gastroenteritis

Causative agent: Noravirus(non enveloped) , Rotavirus( non enveloped)

Classification: NV: positive sense, single RNA virus

RV: double stranded RNA virus

Signs/Symptoms: similar to bacterial gastroenteritis, dehydration

Pathogenesis: infect cells lining intestinal tract and lytic replication. Lysis of cells, loss of functions

Epidemiology: transmitted by fecal to oral route, Noravirus cause 90% of cases.

Diagnosis: serological tests distinguishes among viruses

Treatment: fluid and electrolyte replacement

Prevention: proper treatment of water and sewage, good hygiene and vaccines

Pinworms

Causative agent: enterobius vermiculans

Classification: nematode

Signs/Symptoms: Perianal itching, irritability, decreased appetite, 1/3 of cases asymptomatic

Pathogenesis: female deposits eggs in perianal region at night, eggs can be dislodged and spread disease.

Epidemiology: infections common in children, most common parasitic worm in US.

Diagnosis: identification of eggs or adult pinworms

Treatment: pyrantel pamoate or mebendazole

Prevention: strict personal hygiene

Hepatitis A

Causative agent & Classification: non-enveloped, positive sense, single stranded RNA virus

Hepatitis B

Causative agent & Classification: enveloped, partially double stranded DNA virus

Hepatitis C

Causative agent & Classification:enveloped, single stranded RNA virus, positive sense

Hepatitis A, B, C

Signs/Symptoms: jaundice , abdominal pain, fatigue, vomiting, weight loss

Pathogenesis: liver damage due to host immune response.

Epidemiology: A: fecal to oral. B &C: bodily fluids

Diagnosis: observation of jaundice, enlarged liver, presence of proteins, serological tests

Treatment: supportive care, alpha interferon and nucleotide analogs

Prevention: proper hygiene, protected sex, abstinence, vaccinations