Gastrointestinal Infections

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Gastrointestinal Infections Food Poisoning

• MLAB 2434 Microbiology
• Keri Brophy-Martinez

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General Concepts

• A complete history should be taken
• 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

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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

• 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 10001 ratio
• Colon produces IgA
• Pathogens would have to compete with normal flora

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Risk Factors

• Number of Ingested Organisms
• Median infectious dose (ID50)
• The number of ingested organisms that must be
  ingested to cause a diarrheal illness in 50 of
  exposed individuals
• Achlorhydria
• Inadequate stomach acidity
• Reduction in normal flora
• Use of antibiotics

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Diagnosing Cause of Diarrhea

• 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

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Diagnosing Cause of Diarrhea

• 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

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Enterotoxin-Mediated Diarrhea

• Symptoms
• Rapid onset of diarrhea
• Less than 12 hours
• Lack fever
• Absence of blood or pus
• Point to enterotoxin mediated illness
• Large number of watery stools
• Sometimes gt20 per day

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Enterotoxin-Mediated Diarrhea

• Pathogens
• ETEC
• V. cholerae
• S. aureus
• C. perfringens
• B. cereus
• Other types
• Viral and parasitic can be similar but symptoms
  longer lasting

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Invasive Diarrhea

• Invasion of the bowel mucosal surface
• Symptoms
• Fecal leukocytes
• RBCs
• Sometimes fever
• Organisms
• Salmonella spp.
• Campylobacter spp.
• Shigella spp.
• E. coli
• E. histolitica

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Common Bacterial Agents Causing Diarrhea
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Common Bacterial Agents Causing Diarrhea

• Campylobacter jejuni
• 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

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Campylobacter jejuniFast 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 (contd)

• Salmonella species
• 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

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Common Bacterial Agents Causing Diarrhea (contd)

• Salmonella species (contd)
• Enteric Fever
• 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

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Salmonella speciesFast Facts

• 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 rbcs and wbcs in stool

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Salmonella
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Common Bacterial Agents Causing Diarrhea (contd)

• Shigella species
• 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

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Shigella speciesFast Facts

• Requires a low microbial load
• Fecal WBC lab test
• Observe blood, WBCs, pus
• Culture
• Colorless colonies(NLF) on MAC
• Blue green colonies of HE
• Red/colorless on XLD

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Shigella
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Common Bacterial Agents Causing Diarrhea (contd)

• Diarrheogenic Escherichia coli
• ETEC Enterotoxigenic
• Cause of travelers diarrhea
• EIEC Enteroinvasive
• EPEC Enteropathogenic
• Diarrhea outbreaks in infants in hospital setting
  
• EHEC Enterohemorrhagic
• E. coli 0157H7
• Presence of shiga-like toxin
• Associated with HUS
• EAEC Enteroaggregative
• Chronic diarrhea in HIV patients, travelers,
  children in poor countries

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E. coli O157H7 on MAC and SMAC
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Common Bacterial Agents Causing Diarrhea (contd)

• Vibrio species
• Requires a large microbial load
• Utilize TCBS media
• Inhibits colonic flora
• Differentiates sucrose fermenters from species of
  Vibrio that are non-fermenters
• Stool contains no rbcs or wbcs since it is
  toxin mediated non-inflammatory

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Common Bacterial Agents Causing Diarrhea (contd)

• Clostridium difficle
• Test for the toxin, culture not performed
• Hospital-acquired due to alteration of normal
  flora and use of antibiotics
• Consists of Toxin A B

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Less Common Agents of GI Illness

• Yersinia enterocolita
• Plesiomonas shigelloides
• Aeromonas hydrophilia
• Listeria monocytogenes

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Common Bacterial Agents Causing Diarrhea (contd)

• 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
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Common Parasitic Agents Causing Diarrhea

• Parasitic Infections
• Giardia lamblia
• Ingestion of contaminated water or person-person
  spread
• Nausea, vomiting, flatulence, cramping and
  diarrhea
• Absence of fever and fecal leukocytes
• Entamoeba histolytica
• Fever, grossly bloody diarrhea
• Other rare parasites include
• Cryptosporidium
• Cyclospora
• Microsporidia
• Ascaris
• Stronglyloides
• Trichuris
• And many more

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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

• Rotavirus
• Primarily affects children lt 5 years old
• Spread by fecal-oral route
• Peak incidence from December through June

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Common Viral Agents Causing Diarrhea

• Calicivirus
• 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

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Laboratory Diagnosis of Gastrointestinal Pathogens

• 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

• 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

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Positive Fecal WBC
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Interpretation of Cultures

• All media plates work together to determine the
  presence of a pathogen.
• Routine stool cultures include testing for
• Salmonella species, Shigella species, Aeromonas
  species, Plesiomonas species, and Campylobacter
  jejuni
• Less frequently ordered
• Yersinia, Vibrio, E. coli 0157H7

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Identification Reporting of Isolates

• 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

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Treatment of Diarrhea

• 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!

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References

• 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-cme-1.a
  sp?stypeadvanced
• 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.