Food microbiology & Public Health

• Food hazards


  Foods are complex mixtures of chemicals, including beneficial compounds and those that are potentially harmful
• Types of food hazards

  • Intrinsic (related to food composition)
  • Extrinsic (food as vehicle for exogenous harmful agents)
• Intrinsic food hazards


  • Toxic secondary metabolites produced by plants as defense mechanism against insects, disease, predators
  • Anti-nutritional factors in legumes, pulses
  • Cyanogenic glycosides in cassava, apple seed, almonds, lima beans, yams & bamboo shoots
• Extrinsic food hazards


  • Chemical (pesticide/herbicide residues, hormone residues, cleaning chemicals)
  • Physical (glass, metal fragments, staples, plastic, body parts, dirt, insect parts, rodent feces)
  • Biological (bacteria, fungi, viruses, prions)

  
• Microbiological hazards occur through accidental exposure of pathogens to food or allowing naturally present pathogens to multiply

  
• WHO states the risk of illness by microbial contamination is 100,000 more than pesticides contamination

  
• Foodborne illness


  Illness following the consumption of food (or water) that has been contaminated with an unwanted microorganism or their toxin
• Food poisoning


  Caused by food which looks, smells and tastes normal
• Exotoxins


  Toxic extracellular bacterial proteins or released upon cell lysis

  
• Endotoxins


  Released from Gram-negative cell wall (LPS) by lysis, fever-producing

  
• Toxin designations


  • Enterotoxins (act on intestinal mucosa)
  • Neurotoxins (interfere with normal nervous transmission)
  • Cytotoxins (kill host cells)

  
• Toxins can be named after the producer microorganism or the disease they cause
• Organisms grouped by risk severity


  • Life-threatening, chronic sequelae, long duration, death
  • Severe, moderate, mild
• Microbial transmission


  • Any point from farm to fork: water, air, harvest/slaughter, processing, distribution, retail, preparation
• Food intoxication


  Caused by the consumption of food containing toxins produced by microorganisms
• Foodborne toxicoinfection


  Combination of food intoxication and infection, ingestion of a large number of viable pathogenic cells
• Microorganisms causing foodborne toxicoinfection

  • Clostridium perfringens
  • Bacillus cereus

  
• Foodborne infection


  Caused by consumption of food containing viable pathogens (bacteria, viruses, parasites)
• Bacteria causing foodborne infection

  • Salmonella
  • Pathogenic E. coli
  • Vibrio spp.
  • Campylobacter spp.
  • Yersinia enterocolitica
  • Shigella
  • Aeromonas
  • Vibrio cholera, V. parahaemolyticus, V. vulnificus

  
• Viruses causing foodborne infection

  • Norovirus, rotavirus, astroviruses, coronaviruses, adenoviruses
  • Hepatitis A and E viruses
• Parasites causing foodborne infection

  • Trichinella spiralis, Anisakis simplex, Giardia lamblia, Toxoplasma gondii
• Minimum infectious dose or toxin level is not determined for most pathogens
• Factors affecting infectious dose

  • Host susceptibility
  • Microorganism virulence and antagonisms
  • Food type
• Susceptible populations


  • Elderly
  • Infants
  • Pregnant women
  • Immunocompromised (AIDS, cancer, organ transplants)
  • Predisposing illnesses (alcoholism, diabetes, cirrhosis)
• Gastroenteritis


  Inflammation of intestinal and stomach lining, symptoms include nausea, vomiting, abdominal discomfort and diarrhea
• Diarrhea


  Abnormal faecal discharge characterized by frequent and/or fluid stool, can be acute watery or persistent
• Dysentery


  Inflammatory disorder of the GI tract often associated with blood and pus in the faeces, accompanied by pain, fever, abdominal cramps
• Non-invasive GI tract infection

  • Microbes colonize intestinal lumen, produce enterotoxin that changes electrolyte and water flow
• Invasive GI tract infection

  • Microbes invade intestinal epithelial cells and multiply
• In healthy, well-nourished people, foodborne illness is usually an unpleasant but short-lived episode
• Costs of foodborne illness

  • Individual medical treatment costs
  • Country costs (absence from work, outbreak investigation)
  • Food industry costs (product recall, lawsuits, equipment checks)
• In the USA, the estimated annual cost of foodborne illness from 7 pathogens is over $20 billion
• In the UK, there were 1482 Salmonella cases from 1988-1989
• Invasive pathogens


  • Invade the cells of the intestinal epithelium
  • Pass through the epithelial cells to multiply somewhere
• Invasive pathogens


  • Salmonella
  • Shigella
  • Enteroinvasive E. coli
• Salmonella preferentially invade ileum

  Watery diarrhea
• Shigella & enteroinvasive E. coli invade colon


  Dysentery (usually initiate with watery diarrhea)
• In healthy, well-nourished people, unpleasant episode leads to recovery in a few days
• Costs of foodborne illness

  • Individual (medical treatment costs)
  • Country (absence from work, outbreak investigation)
  • Food industry (directly & indirectly involved, loss of business, recall & destruction of products, lawsuits, equipment checking costs)
• In the USA, estimate of food poisoning costs over $20 billion per year for 7 pathogens