Gastrointestinal Infections & Food Poisoning

1. Gastrointestinal Infections & Food Poisoning MLAB 2434 –Microbiology Keri Brophy-Martinez

2. 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

3. 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

4. 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 1000:1 ratio • Colon produces IgA • Pathogens would have to compete with normal flora

5. 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

6. 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

7. 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

8. 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 >20 per day

9. 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

10. 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

11. Common Bacterial Agents Causing Diarrhea

12. 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

13. Campylobacter jejuni:Fast facts • Grows best at 42 degrees C • Microaerophilic conditions • Capnophilic conditions • Campy plate • Gram-negative curved rods, “seagull wings”

14. Common Bacterial Agents Causing Diarrhea (cont’d) • 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”

15. Common Bacterial Agents Causing Diarrhea (cont’d) • Salmonella species (cont’d) • 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

16. 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 rbc’s and wbc’s in stool

17. Salmonella

18. Common Bacterial Agents Causing Diarrhea (cont’d) • 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

19. 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

20. Shigella

21. Common Bacterial Agents Causing Diarrhea (cont’d) • 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

22. E. coli O157:H7 on MAC and SMAC

23. Common Bacterial Agents Causing Diarrhea (cont’d) • 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 rbc’s or wbc’s since it is toxin mediated & non-inflammatory

24. Common Bacterial Agents Causing Diarrhea (cont’d) • 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

25. Less Common Agents of GI Illness • Yersinia enterocolita • Plesiomonas shigelloides • Aeromonas hydrophilia • Listeria monocytogenes

26. Common Bacterial Agents Causing Diarrhea (cont’d) • 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

27. Bacterial Agents Associated with Food Poisoning

28. 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…

29. Common Viral Agents Causing Diarrhea • Hard to diagnosis due to virus size • Require secondary testing such as cell culture, PCR, EM

30. Common Viral Agents Causing Diarrhea • Rotavirus • Primarily affects children < 5 years old • Spread by fecal-oral route • Peak incidence from December through June

31. 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

32. 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

33. 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

34. Positive Fecal WBC

35. 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 0157:H7

37. 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

38. 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”!

39. 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.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.