Emerging Pathogens

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An overview of pathogenic microorganisms that are significant to the food industry

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Emerging Pathogens

  1. 1. Emerging Pathogens Relevant to Food Safety Dr. Sally Yoder March 31, 2009
  2. 2. What do microbes need to survive? • Nutrients • Water • Temperature • Time
  3. 3. Sources of microorganisms • Environment – Soil – Bodies of water – Wildlife • Food production – Pre-harvest (animals and plants) – Post-harvest processing – Post-process contamination
  4. 4. Food borne disease incidence • 76 million cases of food borne disease each year • 325,000 hospitalizations • 5,000 deaths • FoodNet Surveillance – 1997: 14.3 million people (5%) in 5 states – 2007: 45.5 millions people (15%) in 10 states
  5. 5. Our food system is complex! • Past – Foods were produced and consumed locally – Little variety in foods – Little need for extended shelf life – Most meals prepared and eaten at home – Fewer people in high-risk groups – Food safety and security were not a concern
  6. 6. Our food system is complex! • Present – Global food distribution – Demand for a wide variety of foods (fresh, minimally processed, canned) – Extended shelf life – Prepared foods – Outbreaks can be reported immediately in the U.S. and throughout the world – More people in high risk groups – Increased potential for food terrorism
  7. 7. Microbes can adapt quickly • Mutations and other genetic changes – New virulence factors – Increased resistance to antibiotics • Bacteriophage – Incorporation of new virulence factors/survival mechanisms • Stress adaptation response – Improved survival in harsh environments – Tolerance to heat, cold, osmotic stress, starvation, pH changes, etc. may make organisms harder to control
  8. 8. VBNC • Viable but non culturable – Campylobacter – Listeria monocytogenes – Mycobacterium tuberculosis – Helicobacter pylori – Vibrio cholerae – Some serovars of Salmonella
  9. 9. What is an emerging pathogen? • Natural genetic drift • Previously unrecognized • Newly established link to food • Improve methods of isolation and detection • Improved surveillance • Changing preferences of consumers • Transglobal movement of goods • Adaptation to selective pressure – Antimicrobial resistance – Changes in production practices
  10. 10. Enterohemorrhagic E. coli • Intimin produces A/E lesions (eae gene), affect large intestine and produce Shiga-like toxins • Formerly, called Shiga-like toxin (SLT-I and SLT-II) because of similarity to toxin produced by Shigella dysenteriae – Now called Shiga-toxin (Stx1 and Stx2) – Susceptible cells (in large intestine) have Stx receptor, globotriaosylceramide (Gb3) – Cattle lack Gb3 receptor • O157:H7, non-O157 STEC (O26:H11, O111, O103, O121, O45, O145)
  11. 11. Campylobacter jejuni • Campylobacteriosis – Fairly common cause of food borne illness • Surpassed Salmonella as most common cause of food borne illness in 1997 (CDC) – Easily isolated from stools but is difficult to isolate from foods (low CFU/g and VBNC) – Symptoms are usually flu-like and pass quickly – Serious illness may also occur • Reiter’s syndrome – Joint pain and arthritis for 1 yr after infection • Guillain-Barré syndrome – Neuromuscular paralysis, long-term disability, death • Hemolytic uremic syndrome
  12. 12. Vibrio spp. • V. parahaemolyticus – Most common cause of vibriosis • Everyone is susceptible • Major symptom is watery diarrhea • Large infectious dose (million or more cells) • V. vulnificus – Most severe illness – Leading cause of death in US due to seafood consumption • Usually associated with Gulf Coast oysters – High mortality rate in middle-aged males with cirrhosis or hepatitis
  13. 13. Clostridium difficile • Major cause of nosocomial diarrhea • Toxin A (enterotoxin) and toxin B (cytotoxin) • Infection ranges from: – Asymptomatic colonization (2-3% general population, up to 40% of hospital workers) – Severe diarrhea (C. difficile-associated diarrhea, CDAD) – Pseudomembranosus colitis • Therapeutic use of clindamycin, cephalosporins increases risk of CDAD • Spores can survive for up to 5 mos. in hospital setting • Common cause of illness and death in neonatal pigs • Zoonotic transmission to food?
  14. 14. Yersinia enterocolitica • Unique – “Pathogen that came in from the cold” • 0-1°C observed for pork, chicken, beef • 0-4°C observed in milk → psychrotroph • If present, likely to find other enteric pathogens (Shigella, Salmonella, Campylobacter, etc.) • Animal reservoirs – Swine (common vector of human infection) • Chitterlings consumed by young children in GA – Rodents, ruminants, birds, cats, dogs – Fish, oysters, crabs – Humans are not natural carriers
  15. 15. Bacillus cereus • Aerobic, spore-forming rod – Soil, dust, water – Found at low levels (102 – 104) in many foods • Fresh and processed meat products • Raw milk • Two major kinds of enterotoxin – Diarrheal • Infectious dose ranges from 105 to 108 CFU/g • Cereal dishes, meats, milk, vegetables, fish – Emetic • Infectious dose about 109 CFU/g • Rice, potato, pasta, cheese
  16. 16. Listeria monocytogenes • Ubiquitous! – Soil, streams, natural environment – Mammals, birds, fish, shellfish • Has uncanny ability to survive lethal processes and nonsporeforming • Listeriosis (~25% mortality rate) – Infectious dose ~1,000 cells – Manifestations • Often, flu-like symptoms • Septicemia, meningitis, encephalitis • In pregnant women – Septicemia → may pass to fetus – May cause spontaneous abortion in 2nd/3rd trimester – May cause stillbirth • Infections have declined 42% since 1996-98 baseline (CDC, 2007) • Deli meats, hispanic cheeses, hummus
  17. 17. Salmonella spp. • S. Typhimurium DT 104 – Increase in human disease in UK since 1990s – Livestock → meats – Resistant to ampicillin, chloramphenicol, streptomycin, tetracyclines, sulfonamides, and more • Other drug-resistant strains – Enteriditis, Cholerasuis, other non-typhoidal
  18. 18. Enterobacter sakazakii • Gram-negative rods with unusual thermal resistance • Powdered infant formula – Formula may contain 1 CFU/100 g – 4-log reduction desired in infant formula • May cause meningitis, sepsis, neonatal necrotizing enterocolitis (NEC) – Mortality rate 40-60% – Enterotoxin causes gangrene in infant GIT (NEC) – Preterm infants are more susceptible than full-term
  19. 19. Food borne diseases of former importance • Why aren’t we worried about these diseases? – Cholera – Tuberculosis – Typhoid fever – Trichinosis
  20. 20. Good article to read Tauxe, R. V. 1997. Emerging foodborne diseases: an evolving public health challenge. Emerging Infectious Diseases. 3:425-434.

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