24 Digestive System Infections

Digestive tract

Our digestive system has two general components:

» [__]: Hollow tube from mouth to anus

→ GI tract is used when referring to only the stomach and intestines

» Accessory organs: produce enzymes and substances to break down food

eg. salivary glands, pancreas, liver

Function of Digestive System:

break down food into smaller components so that our body can use them. Absorbed into intestine

Streptococcal

Few species present, but most common organism of mouth microbiota are [__] species

eg. Streptococcus mutans

Protection to prevent overgrowth of microbiota exist in our:

• Mouth » saliva has enzymes and lysozyme and IgA

• Stomach » lysozyme, IgA, and HCl (stomach acid)

» completely sterile due to acid (w/ exceptions like H. pylori)

» bile is also antimicrobial (released from gallbladder to stomach to break down fats)

» peristalsis prevents colonization (moves bacteria along to intestine)

• Intestine » contains microbiota

» small intestine has very few retaining here as they are smaller diameter and propels movement much faster here

» large intestine has greatest amount of microbiota (10¹¹ bacteria/g of feces… 100 billion bacteria)

→ bacteria makes up bulk of feces

eg. Escherichia coli, Bacteriodes (most common in people), Enterobacter faecalis, Klebsiella pneumoniae

→ common cause of urinary tract infections

Cavities

Mouth disease

[__]/dental caries (tooth decay). Lead to erosion of teeth

Causative agent: Streptococcus mutans

» lactic acid bacterium with thick capsule to attach to (eg.) our enamel

» come together to form biofilm for further attachment → creates plaque

» sugar metabolism of bacteria releases lactic acid, which wears down the teeth in [__]

Treatment: drill out [__], replace them with filling, and restore teeth

Periodontal Disease

Mouth disease

[__]: diseases of tissues that support and anchor teeth

Causative agent: Gram-negative anaerobic bacteria in our mouth

» participate in dental plaque build up between gum and teeth that causes [__], such as gingivitis: inflammation of gums

Trench Mouth

Mouth disease

[__]: extreme gingivitis (gum inflammation). Extreme case of Periodontal disease

» extreme damage of gum → extreme bleeding

Causative agent: an oral spirochaete belonging to genus Treponema

» another strain that causes syphilis is from this genus (Treponema pallidum)

Fluoridation

Prevention of Mouth Diseases:

» restrict dietary sucrose (sugary foods)

» [__]: placing fluoride in water, reduced dental caries by 60% in US

→ not prevalent in all areas; some add chloride instead

» brushing and flossing; plaque removal with regular dental appointments

→ tartar: calcified, hardened plaque. can no longer be brushed away like normal soft plaque (must be scraped off)

» sealant, which can prevent dental caries

Helicobacter pylori

[__] Gastritis, Peptic Ulcer Disease, and Gastric carcinoma

Causative agent [__]: flagellated, Gram-negative spiral

» survives by neutralizing acidic environment via urease production

→ breaks down urea to produce ammonia, which shields it from acidity

» only bacteria known to date to cause a cancer (Gastric carcinoma)

Pathogenesis: after [__] produces urease to neutralize stomach acid,

» bacterium use flagella to swim through mucous layer of stomach cells and infect epithelial cells → causes damage and kills mucous producing cells

» mucous no longer effectively produced, stomach cells are exposed to acid and gets destroyed → peptic ulcers and bleeding

H. pylori Gastritis

Stomach disease (very rare)

[__]: inflammation of the stomach lining

» abdominal pain and tenderness of the stomach

» bleeding in stool

» can lead to peptic ulcer disease: characterized by lesions in lining of stomach or duodenum

» repeated infection can lead to gastric carcinoma: stomach cancer

Spread: fecal-oral route (GI tract)

» causative agent found in well waters

» flies that may have been in contact with pathogen in feces act as vectors of disease

» about 50% of world population is infected; chances inc. as we age, and rates higher in lower socioeconomic groups

Diagnosis:

» urea breath test: patients drink urea-containing drink and breath into a breathalyzer that detects for production of ammonia (bacteria releases it!)

» endoscopy: stomach biopsy

» antibody test. can establish time frame of infection by relative amounts of:

IgM = recent infection; IgG = past infection

Prevention: none, as H. pylori is ubiquitous

Treatment: antibiotic and acid reducer

→ increases risk of infection by reducing stomach’s inbuilt antimicrobial defenses

Infectious Intestinal Infections

[__]: infections of the digestive tract that namely impact the intestines. Results in diarrhea

eg. Gastroenteritis, “stomach flu”

» pathogens are contracted by fecal-oral route

→ fingers of unsanitary food handlers

→ flying or crawling insects (eg. cockroaches)

→ contaminated food or water

→ sexual practices with oral-anal contact

» usually no treatment other than rehydration and electrolytes

due to self-limiting responses naturally done by our body to eradicate pathogens

eg. diarrhea, vomiting

Control measures: sewage treatment, handwashing, chlorination of drinking water

» also have PulseNet: DNA subtyping resource that tracks illnesses caused by specific intestinal pathogens → helps determine outbreaks and their sources

Diarrheal diseases caused by [__] are hard to diagnose as they exhibit similar symptoms

information that can help with diagnosis:

» patient travel history and food

» macroscopic and microscopic examination of feces

» lab tests → important in outbreak cases

Diarrhea

Type of Gastrointestinal tract infection

[__]: rapid release of fluid from cells into gut lumen; results from pathogen altering cells in gut to lose water in the form of stools

» loose, watery stools. classified as [__] when it occurs >3x a day

» means by host to forcibly expel pathogen; also aids in dissemination of pathogen

Gastroenteritis

Type of Gastrointestinal tract infection

[__]: watery diarrhea with nausea and cramps

» may involve enterotoxins: toxin that causes diarrhea and vomiting

→ cause water and electrolytes to flow from intestinal cells

→ exotoxins specifically targeting intestine

→ entero = “intestine”

Dysentery

Type of Gastrointestinal tract infection

[__]: bloody diarrhea

» blood and pus show in up feces

» caused by colonization and destruction of epithelial cells in colon/large intestine → can be done by cytotoxins: toxin that causes cell death

Cholera

infectious intestinal disease

[__]: severe diarrhea » 20 L fluid lost daily

» Vomiting and muscle cramps common due to severe dehydration → fatal as severe dehydration can cause damage to vital organs

» “Rice water stool” from extreme loss of water and absence of solid in stool

Spread: fecal-oral route, specifically through fecal-contaminated water

» can drink water, or wash vegetables in contaminated water

» eat contaminated foods like crab and oysters

Epidemiology: Very common disease worldwide, but not in the US

» most US cases involve international travel

Treatment: rapid replacement of fluids and electrolytes (via IV or by drinking)

→ can decrease mortality rate from 30% to 1%

Prevention: have clean water and effective wastewater treatment

» live attenuated oral vaccine against serotype 01 (FDA-approved 2016) for travellers going to areas that are endemic with [__]

Vibrio cholerae

Cholera

Causative agent [__]: gram-negative, curved rod

» 1 million bacteria/mL expelled in feces of Cholera diarrhea

» produces cholera toxin » stimulates intestinal cells to lose electrolytes and water → causes symptoms of diarrhea

Escherichia coli Gastroenteritis

Infectious intestinal disease

[__]: traveler’s diarrhea

Symptoms vary according to virulence of infecting strain

» all lead to vomiting and loose stools → profuse watery diarrhea

» can lead to severe cramps and bloody diarrhea

Can recover within 10 days

Causative agent: E.coli = main cause of traveler’s diarrhea

» E.coli infects travellers that haven’t been exposed to that specific strain of E.coli before → why locals are unaffected

Shiga-toxin producing E.coli

STEC. Most pathogenic strain of E.coli

» foodborne-pathogen. Prototype strain/primary example: E.coli O157:H7

» produces shiga toxin → destroys colon cells

→ can travel to the kidney and cause hemolytic uremic syndrome which leads to kidney failure

→ survivors may require a dialysis later in life

Salmonellosis

Infectious intestinal disease

[__]: results in diarrhea (bloody), abdominal pain, nausea, and vomiting

Spread: fecal-oral route. primarily by foods contaminated by animal feces

» outbreaks primarily caused this way

» commonly contaminated poultry (chicken) and eggs; not as common, but also by tomatoes and alfalfa sprouts

» transmission through pet reptiles (turtle)

» asymptomatic cases of carriers, like “Typhoid Mary”

Prevention and Treatment: Sanitary handling of food and cooking to 165F = kills bacterium

» vaccine for Typhoid fever: severe type of disease caused by S. enterica (50-75% effective)

» surgical removal of gallbladder → eliminates carrier state

Salmonella enterica

Salmonellosis

Causative agent [__]: motile, Gram-negative rods

high infectious dose due to its high sensitivity to stomach acid

Clostridioides difficile Associated-Disease

Infectious intestinal disease

[__]: antibiotic-associated diarrhea (from individuals broad spectrum antibiotics over a long period of time)

Signs and symptoms vary widely:

» mild diarrhea with fever, pain

» colitis or pseudomembranous colitis → inflammation of the intestines that forms pseudomembranes of blood and pus as bacterium grows on intestine

Pathogenesis: infection occurs when C. difficile colonizes the gut due to dysbiosis: disruption of normal microbiota

Prevention and Treatment: oral vancomycin or fidaxomicin may be used (counterintuitive as antibiotics typically cause this disease)

» stop antibiotic treatment

» fecal microbiota transplant (FMT) → replace microbiome of affected individual from a healthy person. repairs dysbiosis and flushes out C. difficile; very effective

Clostridioides difficile

C. difficile Associated Disease

Causative agent [__]: Gram-positive, endospore-forming, obligate anaerobic rod

» formerly belonged to the Clostridium genus (has its own genus now)

» produces one or more cytotoxins (A and B) that are lethal to intestinal epithelium

» colonizes surface of intestine when normal microbiota not present

Norovirus Gastroenteritis

Infectious intestinal disease (Viral)

[__]: abrupt onset of nausea, vomiting, and diarrhea. Short (subsides in 12-60 hours) but awful

Spread: fecal-oral route but also via aerosols and contaminated surfaces

» highly contagious

» millions of cases in the US annually

Epidemiology: causes >50% of foodborne illnesses and common overall on cruise ships and dormitories

Treatment and Prevention: handwashing and disinfectants

» no proven anti-noroviral medications

» no vaccine

Norovirus

Norovirus Gastroenteritis

Causative agent [__]: non-enveloped virus that infects intestinal cells

» shed in feces

» highly contagious → infectious dose of <20 virions

» designated Class B bioterrorism agent due to easy spread (fecal-oral route, air and fomites)

Hepatitis

Disease that results from infection and inflammation of liver

» 3 types: [__] A, [__] B, and [__] C

» most noticeable sign is jaundice: yellowing of skin and whites of eyes

Hepatitis A

Viral Disease in Kidneys

[__]: “infectious hepatitis”

» acute illness that results in: jaundice, fever, fatique, clay-colored feces, and vomiting (in older children and adults). no known chronic form or carrier state!

» asymptomatic (for most young children <6y/o and those 6-14 y/o)

Spread: fecal-oral route or vehicle-born (fecal-contaminated food or water)

» raw shellfish from fecal polluted seawater

» many outbreaks occur at restaurants (eg. McDonalds [__] Outbreak)

Pathogenesis:

» following ingestion, [__] virus goes to liver to replicate

» virus gets released to bile, which gets released into the stomach → shed in feces

Prevention and Treatment: inactivated HAV vaccine for 1-2 y/o and adults

Hepatitis A virus

Hepatitis A

Causative agent [__]: HAV

non-enveloped single stranded RNA virus belonging to Picornaviridae family

» Highly infectious

Hepatitis B

Viral Disease in Kidneys

[__]: hepatitis with an incubation period is 2-5 months (“silent killer/disease”), depending on dose → ninth leading cause of death globally

» acute disease that is asymptomatic to severe

» seldom fatal and clears within weeks or months

» can be chronic disease (happens to 1/5 patients)

→ cirrhosis: scarring of liver, liver failure, liver cancer, etc.

Spread: body fluids (saliva, blood, blood products, semen)

→ sharing of needles, toothbrushes, razors, unsterile tattooing or ear-piercing instruments

→ sexual intercourse makes up 50% of cases in US

Treatment and Prevention: Hep B vaccine → first vaccines given to newborns

» education in high-risk groups on proper use of condoms

» regular screening of adults for HBV

Hepatitis B

Hepatitis B

Causative agent [__]: HBV

Enveloped, dsDNA (double-stranded DNA) genome, member of Hepadnaviridae family

Hepatitis C

Viral Disease in Kidneys

[__]: exhibits similar symptoms to Hepatitis A and B but generally milder

» mild symptoms lead to 80% of infected to develop chronic infection over time

→ cirrhosis, liver cancer

Spread: infected blood

» blood transfusion, tattoos and body piercing with unsterile instruments, needle sharing, toothbrushes, razors, towels, and sexual intercourse

» most common chronic blood-born infection in the US from needle sharing

Treatment and Prevention: no vaccine

» interferon injections and ribavirin

» new group of anti-HCV medications available (95% cure rate)

→ direct acting antivirals (DAAs) interfere with HCV-encoded proteins required for replication of viral genome; a costly and intense treatment wherein a specific strain of HCV was templated for the cure

→ combinations taken orally; variations related to differences in HCV genotypes.

Hepatitis C

Hepatitis C

Causative Agent [__]: enveloped, single-stranded RNA virus belonging to Flaviviridae