Chapter 25 Micro

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Chapter 25 Micro

• Diseases of the Digestive System

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Miscellaneous

• Most of these are transmitted by fecal-oral cycle
• Over 76 million cases of food poisoning in US
  each year
• Over 5,000 deaths from food poisoning each year

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Normal flora in digestive tract

• Few in stomach and small intestine
• Large populations in mouth and large intestine
• 40 of fecal mass is bacterial!
• Bacteria are anaerobic and facultative anaerobes
  in intestine and help with enzymatic breakdown of
  foods and vitamin production (vitamin K)
• Defenses from pathogens include stomach acid,
  Paneth cells in small intestine (phagocytize and
  produce defensins and lysozyme)

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Bacterial diseases of the mouth

• Caries-tooth decay (eating less sucrose really
  helps prevent it)
• Oral bacteria convert sucrose and other
  carbohydrates into lactic acid which attacks
  tooth enamel
• 700 species of bacteria can occur in the oral
  cavity!
• Streptococcus mutans is an important cavity
  causing bacterium
• Accumulations of a biofilm called plaque may
  harbor over 400 species but is mainly
  Streptococcus and Actinomyces.
• Over time this hardens and becomes tarter or
  dental calculus (see figure 25.4)
• Saliva contains lysozyme which helps protect
  exposed teeth

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Periodontal disease

• Inflammation and degeneration of structures that
  support the teeth
• Gingivitis-infection is limited to gums (bleeding
  gums is a sign)
• Periodontitis-gums are inflamed and bleed easily,
  may get pus pockets called periodontal pockets)
• Infection continues and moves toward root tips
• Teeth are loose and may fall out
• Porphyromonas (poor-fi-row-moan-is) is the
  bacteria found in this infection
• Trench mouth is a serious mouth infection with
  foul breath and pain when chewing

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Bacterial Diseases of the Lower Digestive System

• May have 2 types infections or intoxications
• Infection is when pathogen enters and multiplies,
  penetrates intestinal mucosa, and move to organs
• Intoxication-ingestion of a toxin (Staphylococcus
  toxin causes symptoms in a few hours, usually no
  fever)
• Both types cause diarrhea (with blood and mucous
  is called dysentery)
• Gastroenteritis is when there is inflammation of
  stomach and intestinal mucosa
• Diarrhea is major factor in infant deaths in 3rd
  world countries

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Staphylococcal food poisoning

• Leading cause of gastroenteritis
• Toxin is enterotoxin produced by S. aureus
• Resistant to heat up to 60 degrees C for 30
  minutes, drying, radiation, and high osmotic
  pressure
• Staphylococcus is normal in the nose, gets on
  fingers, enters food and can reproduce in food
  (temperature abuse-leaving food out in room temp)
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More on S. aureus

• Produces several toxins that damage tissue and/or
  increase virulence
• Production of toxin of serological type A is
  responsible for most cases is correlated with the
  production of an enzyme that coagulates blood
  plasma (hence they are described as coagulase
  positive bacteria)-used for identification only
• 1 million bacteria per gram of food can cause
  enough toxin to make you sick (re-heating kills
  the bacteria but not the toxin)

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More on Staph

• Custards, cream pies, and ham are high risk
• Hamburger is not usually a problem because of
  competition from other bacteria
• May occur on poultry if it is handled and allowed
  to stand at room temp
• Contamination by human handlers is always a
  problem so refrigerate!
• Toxin can survive 30 minutes of boiling and is a
  superantigen
• symptoms start in 1-6 hours
• vomiting, abdominal cramps, diarrhea
• Recovery within 24 hours

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Shigellosis (Bacillary Dysentery)

• Longer incubation period than Staph (12 hours up
  to 2 weeks)
• Severe diarrhea caused by Shigella (20 BMs in a
  day), cramps and fever also, kills macrophages if
  enter blood
• Spread from person to person reside in GI of
  humans and monkeys only
• 4 species S. sonnei, S. dysenteriae, S.
  flexneri, and S. boydii
• Most common one in U.S. is S. sonnei (mild)
• Worst is S. dysenteriae (Shiga toxin, very bad,
  but uncommon)

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Salmonellosis (Salmonella gastroenteritis)

• Normal resident in intestine of human and many
  animals
• Separated in typhoidal and nontyphoidal
  salmonellae (milder)
• More than 2000 serotypes known, 50 found in US
• Salmonella enterica serotype Typhimurium would be
  S. typhimurium conventionally
• Multiply in the intestinal mucosa, multiply,
  replicate in macrophages if enter blood via M
  cells, incubation time is 12 to 36 hours
• Moderate fever, nausea, abdominal pain and
  cramps, diarrhea
• Recovery depends on how many bacteria, usually a
  few days may shed in feces for up to 6 months in
  some patients

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Cautions for Salmonella

• Meat products like chicken are susceptible to
  contamination
• Hens are susceptible and the eggs get
  contaminated (cook your eggs)
• Pet reptiles (turtles, iguanas, snakes) carry
  this and baby ducks!
• May occur on tomatoes and raw alfalfa sprouts!
• Good sanitation, hand washing, and refrigeration,
  wash cutting boards after cutting raw chicken!

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Typhoid fever

• S. typhi (most virulent serotype) causes this
• Spreads only in human feces (Typhoid Mary)
• S. typhi multiplies inside phagocytes then enters
  liver and spleen where they are cells lyse and
  release the bacteria into the blood stream
• Incubation is 2-3 weeks
• High fever (104), headache, diarrhea in second
  and third week, fever declines when diarrhea
  appears, ulceration and perforation of intestine
  can occur in severe cases (fatal without
  treatment)
• Many become chronic carriers and shed bacteria in
  feces (harbor pathogen in gallbladder)
• Treat with cephalosporins or quinolones ,
  immunity after recovery

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Cholera

• Very serious gastrointestinal disease caused by
  Vibrio cholerae
• Produce exotoxin called cholera toxin that cuases
  host cells to secrete water and electrolytes
  (especially potassium)
• Rice water stools (12-20 liters of fluid lost in
  a day)
• Fluid loss results in dehydration, shock,
  collapse, death
• 50 mortality if untreated
• Associated with brackish water
• Sensitive to stomach acid so people taking
  antacids are more susceptible
• Must drink over 100 million bacteria to get sick

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E. coli Gastroenteritis

• Escherichia coli bind to intestinal cells using
  fimbriae
• Produce toxins that cause GI disturbance
  (Pepto-Bismol is good treatment)
• Travelers diarrhea (montazumas revenge)
• Enterotoxigenic E. coli (ETEC) is not invasive
  but produces an enterotoxin that causes watery
  diarrhea that resembles a mild case of cholera
• Enteroinvasive E. coli (EIEC) invades the
  intestinal wall resulting in fever, inflammation,
  and shigella-like dysentery.

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Shiga Toxin-Producing E. coli

• Enterohemorrhagic E. coli (EHEC) has become a
  problem involving undercooked hamburger meat
• Serotype is O157H7
• 90 of ground beef is contaminated at low levels
• Raw alfalfa sprouts and tomatoes have been
  responsible for many, many cases and petting zoo
• In 6 of population this Shiga toxin causes
  inflammation of colon with profuse bleeding
  (Hemorrhagic colitis)
• Toxin is released into intestine, not blood
• May cause hemolytic uremic syndrome (HUS) leading
  to kidneys failure

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Campylobacter Gastroenteritis

• Campylobacter is a spirally curved gram negative
  bacterium
• Leading cause of foodborne illness in U.S.
• Adapt well to intestinal environment of animal
  host, especially poultry
• Almost all retail chicken is contaminated
• Infective dose is 1,000 bacteria
• Symptoms are fever, cramping abdominal pain,
  diarrhea or dysentery
• Recover in 1 week
• Linked to Guillian-Barre syndrome (temporary
  paralysis)

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Helicobacter peptic ulcer disease

• Caused by H. pylori (30-50 of population in
  developed countries like U.S. have been infected)
• 15 of those people develop ulcers
• People with type O blood are more susceptible
  (also true of cholera)
• Gastric cancer may develop in 3 of those
  (carcinogenic bacteria)
• Test with urea breath test, swallow radioactively
  labeled urea, in 30 minutes CO2 labeled with
  radioactivity can be detected.

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Clostridium perfringens gastroenteritis

• One of the more common forms (symptoms appear
  8-12 hours after ingestion)
• Associated with meats and meat stews contaminated
  with animal intestinal content during slaughter
• Cook meat causes spores to form, reheating
  doesnt hurt spores
• Grows in intestine and produces exotoxin that
  causes abdominal pain and diarrhea
• Usually mild

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Clostridium difficile associated diarrhea

• Produces exotoxin that cause inflammation
  accompanied by increase in fluid secretion and
  permeability of intestinal mucosa
• Occurs in hospitals and nursing homes
• Linked to extended use antibiotics
• Caregivers can get it from patients (take
  universal precautions)
• Kids can get it in daycares
• May range from mild diarrhea to life threatening
  colitis (inflammation and ulceration of colon
  wall)

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Bacillus cereus gastroenteritis

• Common in soil and vegetation
• Heating food doesnt necessary kill spores, which
  germinate as food cools (toxins produced)
• Rice dishes served in Asian restaurants are a
  likely source
• Diarrheal symptoms appear 8-16 hours after
  ingestion sometimes (diarrheal form)
• Other episodes may involve nausea and vomiting
  (2-5 hours after ingestion) called emetic form)
• Usually lasts 24 hours

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Viral Diseases

• Mumps-target is the parotid glands (an accessory
  digestive organ)
• Painful swelling of one or both glands 16-18 days
  after exposure (MMR-measles, mumps, rubella)
• Transmitted in saliva, portal of entry is
  respiratory
• Contagious during first 48 hours before symptoms
  appear

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Mumps continued

• Symptoms include swelling of the parotid glands,
  difficulty swallowing, fever
• In post pubescent males swelling of the testicles
  (orchitis) can occur 4-7 days after onset of
  symptoms
• May burst occasionally, may cause sterility
  occasionally
• Usually complete immunity after recovery

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Hepatitis

• Inflammation of liver
• 5 different viruses cause hepatitis
• Hepatitis A food/feces (fecal/oral)
  contamination
• Single stranded RNA virus without an envelope
• Amount of virus shed in feces is greatest before
  symptoms occur
• Virus can survive on cutting boards, etc for days
  
• Resistant to chlorine disinfectants that are used
  in water

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Hepatitis A (HAV) continued

• 50 of infections are subclinical, especially in
  children
• Symptoms loss of appetite, malaise, nausea,
  diarrhea, abdominal discomfort, fever, chills
• Symptoms last 2-21 days
• Jaundice may occur, dark urine may occur
• Not chronic
• Incubation is 4 weeks average

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Hepatitis B (HBV)

• This is a double stranded DNA enveloped virus
• STD (sexually transmitted), blood products,
  needle pricks)
• 10,000 health care workers a year may become
  infected (immunization now available)
• Transmission by semen stored in sperm banks has
  been documented, mother to infant during birth,
  (administer HBIG to infant quickly)
• May lead to liver disease (caused by immune
  response)

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HBV continued

• Acute HBV-incubation 12 weeks average
• Symptoms may be mild with loss of appetite, low
  fever, joint pain
• If patient gets fulminant HBV they have fever,
  nausea, and jaundice
• 90 recover completely
• Fulminating HBV has high mortality
• Chronic HBV-if symptoms persist for 6 months
• More likely in infants and young children
• 10 of patients become chronic carriers and have
  higher rate of liver disease (cancer)

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Hepatitis C (HCV)

• Transfusion hepatitis
• Delay of 70-80 days before serological tests can
  detect this in blood, so cant be detected in
  blood donor during that time
• Now can detect it within 25 days of infection
  (see box p. 769)
• Single stranded RNA with envelope

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HCV continued

• Silent epidemic
• Has killed more people than AIDS in the U.S.
• May not get symptoms for 20 years
• 85 progress to chronic hepatitis
• 100,000 new cases each year with 5,000 deaths
• 25 develop liver cirrhosis or liver cancer
• Limit exposure, dont share razors, toothbrushes,
  nail clippers
• 80 of Intravenous Drug users are infected
  (IDUs)

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Gastroenteritis

• Rotavirus is most common cause of viral
  gastroenteritis
• 90 of children in U.S. have been infected by age
  3, some cases the parents get it too
• This doesnt usually happen because the parents
  usually had it as kids
• Incubation of 2 or 3 days
• Low fever, diarrhea, vomiting for a week
• May require rehydration and hospitalization
  rarely

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Other

• If you get time after finals, read the rest of
  the chapter. It is full of interesting facts
  about parasites!
• It wont be on the test!