Gastrointestinal Infections & Food Poisoning

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Gastrointestinal
Infections & Food
Poisoning
MLAB 2434 –Microbiology
Keri Brophy-Martinez
General Concepts
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A complete history should be taken
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Foods eaten recently
Exposure to ill patients
Recent travel
Medicinal history
Any underlying illnesses
Diarrhea may be caused by viruses, bacteria,
parasites, food poisoning and non-infectious
processes
Usually acquired by ingesting contaminated
food or beverage
Anatomy of GI Tract
Organisms must be able to survive
gastric acids in order to reach the
small bowel
 In small bowel, motility (peristalsis)
is major host defense. Organisms
can not adhere to intestinal wall
 Generally, a large dose of organisms
is needed to cause disease
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Normal GI Flora
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Stomach contains few organisms
Upper part of small bowel contains small
numbers of Enterococcus sp, lactobacilli,
and diphtheroids, along with Candida
albicans in 20-40% of individuals
Colon contains large numbers of
anaerobes and facultative aerobes in
1000:1 ratio
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Colon produces IgA
Pathogens would have to compete with
normal flora
Risk Factors
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Number of Ingested Organisms
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Median infectious dose (ID50)
• The number of ingested organisms that
must be ingested to cause a diarrheal
illness in 50% of exposed individuals
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Achlorhydria
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Inadequate stomach acidity
Reduction in normal flora
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Use of antibiotics
Diagnosing Cause of
Diarrhea
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History
 Travel to endemic areas of world
 Recreational activities
 Exposure to ill patients
Food
 Detailed history of food eaten 3 days
prior to onset of symptoms
Diagnosing Cause of
Diarrhea
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Physical Exam
 Dehydration
 Toxic megacolon
 Increase in heart rate or decrease in
blood pressure after standing upright
Laboratory Diagnosis
 CBC
 Fecal WBC
 Stool Culture
 O &P
 Electrolyte panel
Enterotoxin-Mediated
Diarrhea
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Symptoms
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Rapid onset of diarrhea
• Less than 12 hours
Lack fever
 Absence of blood or pus
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• Point to enterotoxin mediated illness
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Large number of watery stools
• Sometimes >20 per day
Enterotoxin-Mediated
Diarrhea
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Pathogens
ETEC
 V. cholerae
 S. aureus
 C. perfringens
 B. cereus
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Other types
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Viral and parasitic can be similar but
symptoms longer lasting
Invasive Diarrhea
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Invasion of the bowel mucosal surface
Symptoms
 Fecal leukocytes
 RBCs
 Sometimes fever
Organisms
 Salmonella spp.
 Campylobacter spp.
 Shigella spp.
 E. coli
 E. histolitica
Common Bacterial Agents
Causing Diarrhea
Common Bacterial Agents
Causing Diarrhea
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Campylobacter jejuni
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Most common cause of bacterial diarrhea
in the world
Inadequately cooked poultry, untreated
water, unpasteurized milk, and exposure
to animals with diarrhea
Self-limiting, antibiotics not needed
Manifests with fever, diarrhea and
abdominal cramping
Campylobacter jejuni:
Fast facts
Grows best at 42 degrees C
 Microaerophilic conditions
 Capnophilic conditions
 Campy plate
 Gram-negative curved rods, “seagull
wings”
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Common Bacterial Agents
Causing Diarrhea (cont’d)
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Salmonella species
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Gastroenteritis and Food Poisoning
• Contracted by eating undercooked
meat, poultry, eggs, and contaminated
dairy products
• Nausea, vomiting, and diarrhea 6-48
hours after ingestion
• Usually self-limiting; antibiotics
discouraged because they can induce
“carrier state”
Common Bacterial Agents
Causing Diarrhea (cont’d)
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Salmonella species (cont’d)
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Enteric Fever
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Typhoid fever is most severe
Contaminated food and water
Organisms invade small bowel & colonic tissue
Live and reproduce in monocytes
Can invade gall bladder and produce “carrier
state”
• Symptoms include headache, fever, malaise and
abdominal tenderness
Salmonella species
Fast Facts
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Requires a high microbial load for infection
Culture
 Look for LN on MAC
 Look for blue green colonies with blk
centers on HE
 Look for red colonies with blk centers on
XLD
Fecal wbc lab test
 See rbc’s and wbc’s in stool
Salmonella
Common Bacterial Agents
Causing Diarrhea (cont’d)
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Shigella species
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Diarrhea may have blood and pus
Symptoms appear 12-50 hours after
exposure
Most communicable of the diarrheal
bacteria
Symptoms include: fever, malaise, fatigue
and anorexia
Shigella species
Fast Facts
Requires a low microbial load
 Fecal WBC lab test
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Observe blood, WBCs, pus
Culture
Colorless colonies(NLF) on MAC
 Blue green colonies of HE
 Red/colorless on XLD
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Shigella
Common Bacterial Agents
Causing Diarrhea (cont’d)
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Diarrheogenic Escherichia coli
 ETEC: Enterotoxigenic
• Cause of traveler’s diarrhea
 EIEC: Enteroinvasive
 EPEC: Enteropathogenic
• Diarrhea outbreaks in infants in hospital setting
 EHEC: Enterohemorrhagic
• E. coli 0157:H7
• Presence of shiga-like toxin
• Associated with HUS
 EAEC: Enteroaggregative
• Chronic diarrhea in HIV patients, travelers, &
children in poor countries
E. coli O157:H7 on MAC and
SMAC
Common Bacterial Agents
Causing Diarrhea (cont’d)
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Vibrio species
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Requires a large microbial load
Utilize TCBS media
• Inhibits colonic flora
• Differentiates sucrose fermenters from
species of Vibrio that are non-fermenters
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Stool contains no rbc’s or wbc’s since it is
toxin mediated & non-inflammatory
Common Bacterial Agents
Causing Diarrhea (cont’d)
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Clostridium difficle
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Test for the toxin, culture not performed
Hospital-acquired due to alteration of
normal flora and use of antibiotics
Consists of Toxin A & B
Less Common Agents of GI
Illness
Yersinia enterocolita
 Plesiomonas shigelloides
 Aeromonas hydrophilia
 Listeria monocytogenes
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Common Bacterial Agents
Causing Diarrhea (cont’d)
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Many cases of food poisoning
caused by toxins produced by
bacteria
Bacteria may no longer be alive, but
toxins can cause food poisoning
 Example: S. aureus, Clostridium
botulinum, Bacillus cereus
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Bacterial Agents Associated
with Food Poisoning
Agent
Source of
Contamination
Toxin
Implicated Foods
S. aureus
Nasal passages of
asymptomatic
carriers
Staphylococcal
enterotoxin
Foods with mayonnaise,
eggs, or dairy products,
canned food, frozen
food, processed meats
Clostridium
botulinum
Soil & water
Botulism
neurotoxin
Mushrooms, salami,
improperly canned foods
Bacillus cereus
Environmental
contaminant
Heat-stable
enterotoxin &
heat-labile
enterotoxin
Grains, especially rice
Common Parasitic Agents
Causing Diarrhea
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Parasitic Infections
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Giardia lamblia
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Entamoeba histolytica
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Other rare parasites include:
• Ingestion of contaminated water or person-person spread
• Nausea, vomiting, flatulence, cramping and diarrhea
• Absence of fever and fecal leukocytes
• Fever, grossly bloody diarrhea
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Cryptosporidium
Cyclospora
Microsporidia
Ascaris
Stronglyloides
Trichuris
And many more…
Common Viral Agents
Causing Diarrhea
Hard to diagnosis due to virus size
 Require secondary testing such as
cell culture, PCR, EM
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Common Viral Agents
Causing Diarrhea
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Rotavirus
Primarily affects children < 5 years
old
 Spread by fecal-oral route
 Peak incidence from December
through June
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Common Viral Agents
Causing Diarrhea
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Calicivirus
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Norovirus
• Spread by fecal-oral route by
contaminated food or water or
environmental fomites, person to
person
• Outbreaks on cruise ships
• Cause of stomach flu
Laboratory Diagnosis of
Gastrointestinal Pathogens
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Specimen Collection and Handling
Collect with 4 days of onset of
symptoms
 Stool should be processed ASAP;
NOT refrigerated
 Rectal swabs NOT recommended
 Use of preservatives not
recommended unless test ordered is
an O & P
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Laboratory Diagnosis of
Gastrointestinal Pathogens
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Fecal Leukocytes
• Direct microscopic exam almost
exclusively performed to detect
presence of WBCs and RBCs. Their
presence is due to intestinal wall
bleeding
• Differentiates invasive disease from
toxin-mediated illnesses, viral illness
and parasitic infections
• + WBC: Salmonella, Shigella, Yersinia, EIEC,
Campylobacter, Vibrio
Positive Fecal WBC
Interpretation of Cultures
All media plates work together to
determine the presence of a pathogen.
 Routine stool cultures include testing
for:
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Salmonella species, Shigella species,
Aeromonas species, Plesiomonas species,
and Campylobacter jejuni
Less frequently ordered
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Yersinia, Vibrio, E. coli 0157:H7
Identification & Reporting of
Isolates
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Presumptive identification tests
 Oxidase
 TSI
 Urea
Reporting
 If no pathogens found
• Report “No Salmonella, Shigella, or Campylobacter
isolated”
 Pathogen Isolated
• Identification & quantification
• Any amount significant
• Additional testing may be indicated
Treatment of Diarrhea
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Patients must be watched for dehydration
Antibiotics are NOT effective against viral
pathogens, give supportive care for hydration
Antibiotics may shorten illness by invasive bacteria
or an enterotoxin-mediated process
Antidiarrheal mediations (Lomotil, Pepto-Bismol)
 Primarily used with enterotoxin mediated diarrhea
or viral gastroenteritis
Prophylactic therapy not recommended for
travelers
When traveling, “Boil it, peel it, cook it, or forget
it”!
References
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Engelkirk, P., & Duben-Engelkirk, J. (2008). Laboratory
Diagnosis of Infectious Diseases: Essentials of Diagnostic
Microbiology . Baltimore, MD: Lippincott Williams and
Wilkins.
http://www2.cfpc.ca/cfp/2004/Nov/vol50-nov-cme1.asp?stype=advanced&
http://www.cdc.gov/rotavirus/index.html
Kiser, K. M., Payne, W. C., & Taff, T. A. (2011). Clinical
Laboratory Microbiology: A Practical Approach . Upper
Saddle River, NJ: Pearson Education.
Mahon, C. R., Lehman, D. C., & Manuselis, G. (2011). Textbook
of Diagnostic Microbiology (4th ed.). Maryland Heights, MO:
Saunders.
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