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ENTERIC PATHOGENS AND FOOD POISONING

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ENTERIC PATHOGENS AND FOOD POISONING Powered By Docstoc
					ENTERIC PATHOGENS AND FOOD
         POISONING

     Paul A. Gulig, Ph.D.
   Bread and Butter Lecture
"It may be s$%t to you, but it's my bread and
butter."

Dr. Richard Finkelstein, pioneer of cholera
toxin biology, to medical students at
University of Texas Southwestern Medical
School, ca. 1980.
I. INFECTION VS. PREFORMED TOXIN

    A. Do the bacteria enter the body to
cause disease or do we ingest their
products preformed in our food?

     B. If we ingest preformed toxin,
many of the 7 steps of pathogenesis are
irrelevant.
II. STAGES OF PATHOGENESIS FOR
           INFECTIONS
  A. ENCOUNTER
    1. Where do the bacteria come from?
     a. human FECAL contamination of food and water
(direct, water, soil)

   b. NATURALLY INFECTED ANIMAL FOODS -
meats and dairy products (non-typhoid Salmonella,
Campylobacter, Vibrio vulnificus)

     c. contamination of food (usually fruits and
vegetables) with SOIL - ENVIRONMENTAL (Clostridium
perfringens).

    d. Many enteric pathogens are HUMAN ONLY
(Salmonella enterica serovar Typhi, Shigella)
2. Think about how infection can be
       prevented in terms of:

    food handling (personnel)

         food preparation

other public health considerations.
B. ENTRY: All ORAL

C. SPREAD - three possibilities:
  1. Do not spread past the intestinal mucosa
  2. Invade laterally within the intestines
  3. Invade deeper to the draining lymph nodes,
lymphatics, blood, and all through the body

D. MULTIPLY
  1. lots of food, but little or no oxygen in LARGE
INTESTINE
  2. chemical barriers to growth and multiplication -
acid, bile
  3. competition from normal flora
  4. intracellular pathogens have difficult hurdles
E. EVADE DEFENSES of the alimentary tract:
 1. Origination of disease - MOUTH: no
significant barriers


 2. STOMACH chemical barrier of gastric
acidity, bactericidal, practically sterile.


 3. SMALL INTESTINE: low inoculum from
stomach, digestion (especially bile) and
peristalsis prevent colonization
 4. LARGE INTESTINE: heavily colonized with
obligate ANAEROBES and some facultative
anaerobes; NORMAL FLORA primary
biological defense. Adherence critical.



 5. No constitutive IMMUNOLOGICAL
defenses, but phagocytes during
inflammation, induced/specific defenses -
only sIgA (importance of nursing of
newborns), probably antibacterial peptide
(cryptdins, defensins)
6. Think about WHO is more susceptible when
some of these defenses are compromised.

7. Think about how VACCINATION could
prevent infection and disease.

What forms of protective immunity are
relevant?
 sIgA
 IgG
 CMI – Th1
 CMI – CTL
F. DAMAGE

1. toxins

2. invasion of epithelium

3. attaching-effacing adherence

4. inflammation
5. GENERAL relationship of damage to symptoms (major
method of classifying and discussing different diseases)
   a. vomiting
      - rapid onset
      - usually toxin

   b. diarrhea
      - large volume, usually without blood or pus
      - usually small intestinal effects (secretory bowel)
      - usually from toxin
      - bloody diarrhea does not equal dysentery

   c. dysentery
       - smaller volume, pus (white cells), can be bloody,
fever, abdominal pain
       - usually from large intestine (inflammatory bowel)
       - usually invasive organisms
G. MOVE TO NEW HOSTS - SEE ENCOUNTER
   Considerations in Diagnosis
• Symptoms
  – vomiting
  – diarrhea
  – dysentery
• Time frame relative to consumption
• History
  – epidemiology (other cases?)
  – type of foods eaten
  – drugs (antibiotics, etc.)
  – travel
III. FOOD INTOXICATION (FOOD
POISONING)

 - NO INFECTION (no viable bacteria need
to encounter the host)

 - toxin preformed in the food as a result of
bacterial contamination (soil or human)
  A medical student attended a picnic at the Santa Fe
River. She did not consume the chicken salad,
hamburger, or ice cream, but did eat lots of potato
salad, hot dogs, and beer. Four hours after
returning home the student experienced profuse,
projectile vomiting for several hours, followed by
two loose stools. Vomiting continued even though
her stomach was empty. No fever, or blood or pus
in stools were noted by the student, who assumed
she "drank too much." The following morning, the
student ate and drank nothing, and was fine by the
afternoon.
A. Staphylococcal food poisoning -
Staphylococcus aureus
 - rapid onset, profuse vomiting, possibly
diarrhea

 1. ENCOUNTER - contamination from
INFECTED FOOD HANDLER (human reservoir)

 2. DAMAGE - enterotoxins released into food
  a. heat stable
  b. superantigens
  A 55 year old male in good health ate home-canned
green beans which had been stored for several
months. The next day he experienced double and
blurred vision, which he attributed to sleeplessness
and stress over his impending lay-off. However, the
following day he experienced dryness in his mouth
and difficulty swallowing, which progressed to
weakness in his neck muscles. Again, he attributed
these symptoms to stress. Finally, on the third day,
he began to experience respiratory distress with
shallow and frequent breathing. Examination upon
admission to the hospital examination revealed fixed
and dilated pupils, despite clear sensorium. The
patient was afebrile. The flaccid paralysis of neck
and upper body muscles was noted.
B. Botulism - Clostridium botulinum
  - gram-positive rod, obligate anaerobe, spore
former

  1. ENCOUNTER - spores from soil-
contamination (i.e., vegetables) germinate in
anaerobic but incompletely processed CANNED
(autoclaved) food
  2. botulinum toxin
     a. neurotoxin - causes flaccid paralysis by
inhibiting release of acetylcholine (no stimulatory signal)
     b. A-B type; heat labile
     c. encoded on LYSOGENIC BACTERIOPHAGE

  3. DAMAGE – SYMPTOMOLOGY:
    ocular -> pharyngeal -> respiratory paralysis ->
death

   4. TREATMENT - supportive therapy (respiratory),
anti-toxin

  5. other diseases – INFECTIONS - infant botulism
and wound botulism
C. Bacillus cereus - rice-associated diarrhea and
vomiting
 - gram-positive rod, aerobic spore former

 1. ENCOUNTER - environmental - naturally
contaminated rice

  - improperly cooked and held at warm temperature to
enable bacteria to grow

2. DAMAGE - enterotoxins secreted into food

  Can also be produced in intestines after ingestion of
vegetative cells during sporulation.
WHY?
  Why did 3 people die from eating a
    health food – fresh spinach?

 What kind of organism can do this?

Why are children particularly at risk for
          kidney damage?

What could have been done to prevent
            this tragedy?
IV. TOXINOGENIC INFECTIONS
    enterotoxin, DIARRHEA
 During spring break, three medical students volunteered to go to
Peru to help out in the rural clinics. Three other students went to
Cancun Mexico to have a good time. The students in Peru helped
vaccinate infants and children and care for the numerous cases of
enteric diseases. Their break was rewarding and uneventful.

  The students in Mexico made serious attempts to eat only
processed food and bottled beverages. However, during their
third night in town and after drinking too many bottled alcoholic
beverages, they ventured into the market where they consumed
numerous fresh tropical fruits. Late the following day they began
to experience frequent, loose stools, with abdominal tenderness.
None of them experienced fever, and gross observation of their
stools failed to reveal blood or mucus. They consumed copious
quantities of Pepto-Bismol and non-alcoholic fluids (Gator-Aid)
which they had brought along, just in case. After two days of
seclusion in their hotel bathrooms, they recovered just in time to
return home.
  Upon returning from Peru, one of the students experienced
a sensation of intestinal fullness and increased bowel
sounds. This was followed within hours by massive watery
diarrhea which progressed from a brown color to clear and
containing flecks of, what looked like, mucus. Being an
independent type, the student examined his stool by Gram
stain in the teaching lab and noticed gram-negative comma-
shaped organisms, but no RBCs or WBCs. This student had
no fever, but lost five pounds before seeking medical
attention. The second student from Peru experienced a
disease process very similar to the Mexico tourists, and the
third Peru student experienced no intestinal problems all. All
of the Peru students ate and drank similarly from communal
food sources.
      Vibrio cholerae
    Web Based Teaching


http://www.snaption.net/med/cholerae.htm
 A. Vibrio cholerae - cholera

  - severe - rice water stool, death by
dehydration; many cases are asymptomatic-
mild

  - gram-negative, comma shaped bacterium

  - Classification:
    -O antigen O:1 (Inaba and Ogawa serotpyes)

   -Biotype: El Tor and Classical
         Vibrio cholerae




http://www.textbookofbacteriology.net/vcfla.jpeg
  B. Enterotoxinogenic Escherichia coli
(ETEC) - traveler's diarrhea

  - mild to severe self-limiting diarrhea

  - gram-negative rod; enteric bacterium
Escherichia coli
    1. ENCOUNTER - contaminated water,
vegetables

  2. ENTRY - adherence factors – pili

  3. SPREAD - none; localized to epithelial
surface
4. DAMAGE - TOXINS

 a. heat labile enterotoxins - cholera toxin and E.
coli LT; antigenically related

   i. A-B type toxins
   ii. B portion binds to GM1 gangliosides of host
cells
   iii. A portion ADP-ribosylates stimulatory G
protein of adenylate cyclase locking it in ON form
   iv. increases intracellular cAMP
   v. secretion of water and salts into lumen of
intestine
   vi. absorptive functions intact; no cellular
damage
              Cholera Toxin


                                              A



                                                 Bx5



http://www.rctb.net/images%5CCholera_holotoxin_cartoon.jpg
 b. heat stable enterotoxin (ST) of E. coli
  i. very small protein - single chain peptide
  ii. binds quanylin receptor – acts like
hormone
  iii. increases cyclic GMP
  iv. stimulates water and salt secretion

 c. ST, LT of E. coli are plasmid encoded

 d. CT is encoded by phage - lysogenic
conversion
5. EVADE DEFENSES - none in non-immune
host

6. VACCINES
 a. cholera - killed cells injected
intramuscularly, but live, attenuated under
development

7. TREATMENT
   a. cholera - oral or i.v. fluid and electrolyte
replacement + antibiotics
   b. ETEC – symptoms + antibiotics?
   A four year old boy vacationing in the northwestern United
States ate a rare hamburger at the Greasy Grill. Late the
following night (about 36 hours later) he was awakened by
severe abdominal cramps, primarily in the right lower
quadrant of the abdomen. Later in the morning , watery
diarrhea occurring every 15-30 min developed, initially with
small amounts of visible blood. Later in the day, bright red
stools with what seemed to be pure blood appeared. He was
nauseated, but not vomiting. His parents took him to an
emergency care center later in the day. He had no fever, and
examination of the abdomen was unremarkable except for
increased bowel sounds. Because of an elevated WBC
count, the boy was hospitalized. Frankly bloody stools
continued, and a barium enema was performed, revealing
edema of the ascending and transverse colon with areas of
spasm. He was treated with i.v. fluids, antibiotics were
avoided (why?).
C. Enterohemorrhagic E. coli (EHEC)
   - bloody diarrhea, hemolytic-uremic syndrome
   - O157:H7 serotype
   - sorbitol-negative

1. ENCOUNTER - contaminated food from animals,
mainly beef, also apple cider (and swimming pools);
major problem - bovine fecal contamination

2. ENTRY - adherence through specialized
mechanism
   a. resistant to stomach acid (low infectious dose)
   b. attaching-effacing lesion
   c. identical to EPEC (see below)
  Attaching-Effacing Lesion




http://cahfs.ucdavis.edu/graphics/em_scans/ecoli_5-72.jpg
3. DAMAGE -
 a. although bloody diarrhea appears like
invasive dysentery (e.g., Shigella, see below),
the bacteria do not invade the epithelium,
therefore little fever or pus in stool

 b. secrete a Shiga-like toxin (SLT/Stx) (see
Shiga toxin, below)

 c. causes severe tissue damage in the large
intestine, distal ileum because of capillary
thrombosis
 d. SLT may be transported into the blood
where damage occurs to endothelial cells of
the vasculature or kidneys

 e. hemolytic uremic syndrome (HUS) -
mainly in very young; renal endothelial
damage; microangiopathic hemolytic anemia;
thrombocytopenia; thrombosis of glomerular
capillaries

 f. different type 3 secreted protein,
stimulates ATP secretion, converted to
adenosine in lumen, fluid secretion
4. Diagnosis
     a. MacConkey agar with sorbitol
     ● EHEC is sorbitol-negative (what color will
they be?)
     b. test for Stx

5. Treatment
     a. Symptomatic and supportive
     b. Avoid antibiotics because they can
stimulate Stx production and HUS
D. Clostridium difficile

Antimicrobial Associated Diarrhea and
Pseudomembranous Colitis

  - gram-positive rod, obligate anaerobe,
spore former
    Clostridium difficile




http://www.textbookofbacteriology.net/nfC.difficile2.jpeg
  1. ENCOUNTER - normal flora

  2. DAMAGE - TOXINS
   a. Toxin A - increases membrane
permeability and inflammation in intestinal
mucosa

   b. Toxin B - cytotoxin resulting in necrosis
and epithelial destruction

    c. result in mild/watery diarrhea to bloody
diarrhea

   d. diagnose by assay for toxins
Pseudomembranous colitis caused by C. difficile




    http://www.cortlandtforum.com/content/fileadmin/template/issue_archive/2006/June_06/PopQuiz2June06.gif
E. Vibrio parahemolyticus (self study?)
  - halophilic vibrio
  - difficult to grow

1. ENCOUNTER - improperly cooked seafood
(environmental)
   - oyster epidemic summer 1999

2. DAMAGE
  a. cramping, pain, vomiting, diarrhea, self-
limiting
  b. virulence factor - hemolysin (Kanagawa
factor)
  c. possibly also invasion of epithelium
IV. INVASIVE INFECTIONS

- invade cells and tissue

- DYSENTERY or BLOODY DIARRHEA
 A 22-month-old boy of a middle class family attended a day
care center which had experienced several cases of diarrhea
earlier in the week. He became febrile (39C), lost his appetite,
and developed watery diarrhea. The next day there was less
diarrhea, but his parents noted mucus and bloody tinge to his
stool. The number of bloody stools increased, and the boy
began to vomit. The boy's parents took him to the
emergency room where his fever was noted, and he was
found to be dehydrated and had lost two pounds over the
past two days. Microscopic examination of the stool sample
revealed WBCs and RBCs. The child was placed on i.v.
rehydration therapy and antibiotics and gradually recovered
without lasting problems.
A. INVASION RESTRICTED TO INTESTINAL
MUCOSA - primarily dysentery

  1. Shigella dysenteriae, S. flexnerii, S. sonnei,
and Enteroinvasive E. coli (EIEC)
    - gram-negative rods, enterics
    - Shigella and EIEC are essentially identical
organisms
    - symptomology: early stage - diarrhea,
progressing to dysentery (blood, pus in stool),
abdominal pain, tenesmus, fever
a. ENCOUNTER - humans only
     i. S. sonnei most common in U.S.
     ii. S. flexneri next
     iii. S. dysenteriae not endemic in U.S.

b. Entry
     i. highly acid resistant
     ii. small inoculum (10-100 cells)
     iii. infection in colon

c. SPREAD: laterally in intestines
Dysentery
c. DAMAGE:

 i. plasmid-encoded cellular invasion of
epithelial cells of the colon (type III secretion
system for injection of proteins into host)

 ii. lyse vacuole and replicate in cytoplasm

 iii. use host actin polymerization to move
directly from cell to cell

 iv. cause cell death (cytotoxicity) and
ulceration, inflammation
 v. Shigella dysenteriae (ONLY) - potent
cytotoxin (Shiga toxin)

  - Shiga toxin is an A-B toxin

  - inactivates ribosomes (deglycosylates
rRNA) halting protein synthesis and killing the
host cell

  - associated with hemolytic uremic
syndrome
d. EVASION OF DEFENSES - intracellular
location sequesters organisms from
phagocytes, apoptosis of macrophages



e. VACCINES: none to date, working on
attenuated Shigella
B. INVASION PAST THE INTESTINE -
many types of symptoms/disease
depending on degree of invasion
   During the same spring break as for case 1, a
second year medical student went to a picnic at
some springs on the Santa Fe River. Two days after
the picnic, she had a brief period of vomiting
followed by severe abdominal cramps and large
volume, watery diarrhea. The diarrhea has
continued for three days. She had a temperature of
38C and a few leukocytes but no RBCs in her stool.
She had abdominal tenderness and hyperactive
bowel sounds. She ate chicken salad, rare
hamburger, and homemade ice cream at the picnic.
The student took over the counter anti-diarrheal
agents, and the symptoms resolved on the second
day of home-treatment, so she did not seek medical
help.
1. Salmonella enterica: typhoid fever (enteric
fever), gastroenteritis, septicemia (vascular
endothelium), focal infections; carrier state
also possible

   - Nomenclature: One species (Salmonella
enterica) with thousands of serovars (Typhi,
Typhimurium, Enteritidis, etc.). Most of us
take a shortcut and use the genus and
serovar names.
a. typhoid (enteric) fever - S. typhi, S. paratyphi

  i. symptomology: few intestinal symptoms, mainly
systemic - fever, shock, headache, myalgia,
lethargy, splenomegaly, hepatomegaly

 ii. ENCOUNTER: only in humans, but epidemiology
can have indirect spread

  iii. SPREAD
    - invade gut-associated lymphoid tissue of small
intestine
    - infect lymph nodes, blood, spleen, liver, bone
marrow, other focal organs (e.g., gall bladder)
(similar to TB in that it can go all over the place)
iv. EVADE DEFENSES
  - resistance to phagocytes (intracellular) and
serum complement
  - cell-mediated immunity more important
  - S. typhi and S. paratyphi C - Vi capsular antigen
also involved in virulence

v. DAMAGE: endotoxin + inflammation

vi. vaccine: for S. typhi
 - killed cells administered i.m. - not good
 - new vaccines - attenuated strains fed orally to
stimulate mucosal immunity
   During the same spring break as for case 1, a
second year medical student went to a picnic at
some springs on the Santa Fe River. Two days after
the picnic, she had a brief period of vomiting
followed by severe abdominal cramps and large
volume, watery diarrhea. The diarrhea has
continued for three days. She had a temperature of
38C and a few leukocytes but no RBCs in her stool.
She had abdominal tenderness and hyperactive
bowel sounds. She ate chicken salad, rare
hamburger, and homemade ice cream at the picnic.
The student took over the counter anti-diarrheal
agents, and the symptoms resolved on the second
day of home-treatment, so she did not seek medical
help.
b. gastroenteritis - thousands of serovars, but
predominantly S. typhimurium and
S. enteritidis

 i. symptomology - nausea progressing to
diarrhea and severe abdominal pain, can be
dysentery in severe cases, infrequent
bacteremia in healthy, but recurrent
bacteremia in immunocompromised

 ii. ENCOUNTER: not human specific (but
human to human possible), found in animals
(poultry, bovine)
 iii. SPREAD

   - invade the epithelial cells of the small
intestine using adherence factors and
invasion factors to stimulate endocytosis by
host (type III secretion)

  - infection usually limited to intestines
                          Movie Time !!!



http://bioteach.ubc.ca/TeachingResources/MicrobiologyImmunology/FinlaySalmonella.mov




                      Salmonella infecting a macrophage
iv. MULTIPLICATION: virulence plasmid -
increasing growth rate within macrophages

v. EVADE DEFENSES
   - resistant to phagocytes (intracellular)
   - resistant to complement (LPS)

vi. DAMAGE: inflammatory diarrhea,
inflammation and endotoxin for systemic
infection
c. bacteremia and metastatic infection –

 i. symptomology: fever, shock, endotoxin
effects; localized metastatic disease

 ii. pathogenesis – similar to gastroenteritis
d. asymptomatic carrier state -
shedding of bacteria in feces can last as
long as 20 weeks after symptoms clear
2. Campylobacter jejuni

 - vibrio-shaped (gull-shaped) cells

 - leading cause of bacterial diarrhea, can be
as severe as dysentery

 - culture: 42ºC, Campy agar
Campylobacter
 a. pathogenesis similar to Salmonella and
Shigella

 b. ENCOUNTER - animal foods (poultry)

 c. SPREAD and DAMAGE
  i. diarrhea to severe dysentery
    - association with Guillain-Barre
Syndrome (paralysis, inflammatory
neuropathy, autoimmune) - LPS cross-
reactivity with gangliosides

 d. other virulence factors unknown
3. Vibrio vulnificus - a Florida and gulf coast
specialty
    - sepsis and wound infection in susceptible
people (e.g., hemochromatosis, liver disease)

  a. ENCOUNTER - eating raw oysters
(environmental) and wound infection

 b. ENTRY - orally or in wound

 c. SPREAD - highly invasive through tissues and
blood

  d. MULTIPLICATION - replicates very rapidly in
tissues
  e. EVADE DEFENSES - EXTRACELLULAR
with capsule - disease mainly in
hepatocompromised with elevated levels of
iron in plasma

  f. DAMAGE - extracellular enzymes and
toxins, stimulate vascular permeability
leading to shock, DEATH WITHIN DAYS OF
CONSUMING OYSTERS

 g. SPREAD TO NEW HOSTS - NO, humans
are dead end
Vibrio vulnificus bullous lesions




 http://www.muhealth.org/~library/info/news/vibrio_warning2.jpg
V. ENTEROPATHOGENIC PATHOGENESIS -
Enteropathogenic E. coli (EPEC) and
ENTEROAGGREGATIVE E. coli (EAEC) - diarrhea in
infants and children

  A. EPEC adhere through intimate association
(attaching-effacing lesion leading to destruction of
microvilli)
   - plasmid-encoded pili
   - injection of bacterial proteins into host epithelial
cells (type III secretion)
   - one protein acts as receptor for EA factor
   - stimulates secretion of ATP - diarrhea

 B. EAEC - poorly understood - Toxin
                     Movie Time Again !!!


http://bioteach.ubc.ca/TeachingResources/MicrobiologyImmunology/FinlayEcolicdMusic.mov




         EPEC infecting an epithelial cell – Attaching/Effacing lesion
V. Gastric and duodenal ulcer - Helicobacter
pylori
  - similar in morphology to Campylobacter

 1. ENCOUNTER - human to human spread

 2. SPREAD - survives in stomach tissues -
urease production neutralizes acid

 3. EVADE DEFENSES - apoptosis of T cells,
antigenic mimicry - LPS/Lewis antigens
      Helicobacter pylori (EM)




http://microbewiki.kenyon.edu/index.php/Image:H.pylori.gif
 4. DAMAGE
  a. inflammation

  b. vacuolating cytotoxin

  c. epidemiological association with gastric
adenocarcinoma

 5. DIAGNOSIS – biopsy and urease staining*,
urease breath test, culture

 6. TREATMENT - multiple antibiotics
Gastric ulcer caused by H. pylori




   http://microbewiki.kenyon.edu/index.php/Helicobacter

				
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