Non-Bacterial Agents of Food-Borne Illness

    Cards (92)

    • MICR3265
      Course code for Microbiology of Food
    • Lectures 17 & 18: Non-bacterial agents of food-borne illness - Mycotoxins, Biotoxins & Viruses
    • Presented by Dr. Kelly Brathwaite
    • Mycotoxins
      Secondary metabolites naturally produced by certain filamentous fungi (Moulds)
    • Mycotoxins
      • May contaminate a variety of different crops (e.g., cereal, nuts, spices, fruits) in the field (before harvest) and during the storage of grains, dried fruits for example (post-harvest)
      • ≈ 25% of global food crops are contaminated with fungal toxins every year
      • A mouldy food is probably infected by several species of moulds & contaminated by several different mycotoxins
      • Contamination of food & feed grains is a serious economic problem for grain producers and processors and food safety problem due to their impact on human and animal health
    • Fungi growth conditions
      Warm and humid conditions (T & aw)
    • Mycotoxins
      • More than 400 identified mycotoxins are produced by some 200 varieties of fungi such as Fusarium, Aspergillus and Penicillium (≈ 27 toxins)
    • Most studies focus on aflatoxins, ochratoxin A and the Fusarium toxins fumonisin, zearalenone & deoxynivalenol/nivalenol due to food safety and economic losses
    • Ochratoxin A (OTA)

      Produced by Aspergillus ochraceus in tropical regions and Penicillium verrucosum in cold regions (Western Europe, Canada & certain areas of South America)
    • Penicillium islandicum
      Produces 2 hepatotoxins (injurious to the liver) causing yellow rice disease: cyclochlorotine and carcinogenic luteoskyrin
    • Mycotoxin toxicity
      • Mutagenic: causing DNA damage
      • Carcinogenic
      • Teratogenic: causing malformation of an embryo/fetus (aflatoxins, ochratoxin A & zearalenone)
      • Nephrotoxic: damaging of the kidney
      • Hepatotoxicity: damaging of the liver
      • Cytotoxic: damaging of the cells
      • Immunotoxic: damaging of the immune system by destroying immune cells
    • Acute intoxication
      Exposure to high-dose mycotoxin; symptoms develop rapidly such as abdominal pain & diarrhoea
    • Chronic intoxication
      Exposure to low-level mycotoxins for long period causing impairments in the liver, kidney, and immune system that can result in liver of kidney cancer
    • Mycotoxin intake by feed or food causes chronic intoxication rather than acute symptoms
    • Mycotoxins
      • Aflatoxins B1, B2, G1, G2
      • Ochratoxin A (OTA)
      • Patulin
      • Trichothecenes: T2, Deoxynivalenol (DON)
      • Zearalenone
    • Aflatoxins
      • Produced by Aspergillus flavus & A. parasiticus
      • The 1st mycotoxins to be identified, recognized in 1960
      • Over 100,000 turkey died in UK by feeding on peanut meal contaminated with Aspergillus flavus producing aflatoxin
      • In 2006 - Several outbreaks of aspergillosis in Cumuto and Valencia farms in Trinidad: more than 6,000 chickens
    • Types of aflatoxins
      • B1, B2, G1, G2, M1, M2
    • Aflatoxin toxicity
      • Hepatotoxic (liver damage), chronic hepatitis (jaundice & cirrhosis), liver cancer, immunotoxic, teratogenic
      • B1 more toxic than (>) G1 > B2 > G2
    • Heat processing, such as ultrahigh-temperature (UHT) treatment, pasteurization, roasting, and baking, and also cold storage do not affect aflatoxin in foods since they are fairly stable
    • Ochratoxin A (OTA)

      • Potentially nephrotoxic (damaging of the kidney), carcinogenic, hepatotoxic, immunotoxic & teratogenic
      • Produced by Aspergillus ochraceus in tropical regions and Penicillium verrucosum in cold regions (Western Europe, Canada & certain areas of South America)
      • Kidney necrosis (especially in pigs)
      • Toxin accumulates into fat animals (poultry, pigs, cow) eating contaminated feeds & can be ingested by humans eating these meats
      • Mainly associated with cereals (barley, wheat crops)
    • Foods where ochratoxin A may be found
      • Bread made with contaminated cereal
      • Dried beans, soybeans, coffee beans, cacao, moldy tobacco, country cured hams, nuts & peanuts, grape juice, red wine, beer, spices & dried fruits
    • Patulin
      • Produced by several spp. of Penicillium & Aspergillus
      • Toxin production at min aw 0.81, also in lower temperatures (0–24°C)
      • In 1942: potentially useful antibiotic w. wide spectrum of activity
      • In 1959, recognized as mycotoxin after an outbreak of poisoning of cattle, being fed on germinated barley malt sprouts
      • Symptoms: acute (lung & brain edema, liver & kidney damage, and toxicity to the immune system), chronic (neurotoxic, teratogenic, immunotoxic, skin lesion & cancer)
      • Some outbreaks are associated with badly stored materials such as apples infected with P. expansum (chapter 5: blue mold, soft rot)
      • Fresh apple juice: limit of 50g/l
      • The presence of patulin in fruit juice is a useful indicator of very poor quality of fruits used in its manufacture
      • Stable at relatively low pH, but destroyed during the fermentation of apple juice to cider
    • Deoxynivalenol (DON)

      • DON in carcinogenesis Group 3 of Trichothecenes toxins
      • Known as vomitoxin, is the most commonly detected in grains such as wheat, barley, oats, rye, and corn and less often in rice, sorghum
      • DON appeared in 81% of livestock feed from 81 countries worldwide
      • DON and Nivalenol inhibit cell metabolism (e.g., protein, DNA, and RNA synthesis), affect cell division and mitochondrial functions
      • DON is less toxic than Nivalenol
      • DON also shows teratogenic, neurotoxigenic, and immunosuppressant effects
      • Major symptoms such as abdominal discomfort, diarrhea, vomiting, and inflammation of the throat, weight loss, and anorexia
    • Mycotoxin control/prevention
      • Good Farm Management Practice (GFMP)
      • Preventing plants from become infected with moulds
      • Adequate drying & storage of foods and feeds
      • Biological control e.g. infecting plant in the early stage with nontoxigenic strains of A. flavus to prevent the colonization of toxigenic strains in peanuts plants
      • Good manufacture practices (GMP)
      • Remove rotten & damaged fruits to be used for juice production
      • UV light used to screening for aflatoxins (fluorescence) in corn, cottonseed & figs, but not in peanuts since they autofluoresce: Peanuts containing aflatoxins are removed by electronic colour-sorting machines, which detect discoloured kernels
    • Mycotoxin control/prevention (chemical treatments)
      • Ozone, H2O2 , & Anhydrous ammonia gas (↑T,P) used in peanut meals (95-98% reduction), more effective when applied together with heat
    • Mycotoxin regulations
      • FDA: Aflatoxin M1 in milk: 0.5 ppb
      • Aflatoxins in human food: 20 ppb, 30 ppb (FAO/WHO)
      • Patulin in apple juice: 50 ppb
      • DON: 1 ppm in finished wheat products that may be consumed by humans
      • Barbados guidelines for mycotoxins
    • Scombroid (Scombrotoxin or Histamine) food poisoning

      Caused indirectly by bacteria
    • Histidine
      A naturally occurring amino acid that is present in higher proportions in the muscle of certain fish species, particularly those of the Scombridae family
    • Scombroid food poisoning is primarily associated with consumption of fish flesh in species rich in free histidine
    • Histidine decarboxylase
      • Certain bacteria produce the enzyme histidine decarboxylase during growth, which breaks down free histidine present in the fish (post-mortem) → histamine
      • Enzyme can remain active even after cooking
    • Commodity
      • Mycotoxin(s)
      • Limit (µg/kg)
    • Commodity
      • aflatoxins B1,B2,G1,G2
      • 20
    • Commodity
      • aflatoxin M1
      • 0.5
    • Commodity
      • aflatoxins B1,B2,G1,G2
      • 50
    • Non-bacterial agents of foodborne illness
      Scombroid (Scombrotoxin or Histamine) food poisoning (caused indirectly by bacteria)
    • Number of histamine poisoning outbreaks reported in the European Union during the years 2010-2018 [27-35]
    • Fish species with high histidine
      • Scombrid (mackerels, tunas, and bonitos)
      • Clupeid (herrings)
      • Carangid (jacks)
    • Histidine decarboxylase
      Certain bacteria produce the enzyme that breaks down free histidine present in the fish (post-mortem) → histamine
    • The enzyme can remain active even after the bacteria responsible for producing it have been inactivated or killed
    • The enzyme continues histamine production slowly at refrigeration temperatures and remains stable if frozen, thus allowing it to rapidly recommence activity after thawing