FOOD MICROBIOLOGY

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FOOD MICROBIOLOGY
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PROBLEMS

• food is kept at temperatures that microbes like
  to grow
• food is a good growth medium high in nutrients
• food is handled much more than water or milk
• there are few standards that govern the handling
  of food

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FACTORS THAT AFFECT FOOD SPOILAGE "INTRINSIC
FACTORS"

• food composition -
• carbohydrates - hydrolysis and production of
  acids and alcohols (souring)
• proteins - putrifaction (break down of proteins
  and production of foul smelling amines) (souring,
  sliminess, odor, bitterness)
• fats - hydrolysis and breakdown of fatty acids
  (bitterness, rancidity)

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Fig. 40.1
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• water availability
• pH
• low pH favors growth of fungi
• oxidation-reduction potential (cooking foods can
  make components more available to bacteria by
  lowering the ox-red potential)

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• physical structure -
• skin on fruits
• ground foods
• natural antimicrobial substances
• lysozyme in eggs and milk
• coumarin in fruits and vegetables
• spices (sage, rosemary, hot peppers, cinnamon,
  garlic, cloves, oregano, mustard, basil)
• polyphenol compounds in green and black teas

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"EXTRINISIC FACTORS"

• temperature
• humidity higher humidity encourages growth
• atmosphere higher CO2 and O2can inhibit growth
  of bacteria and fungi

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TRANSMITTED FOOD BORNE ILLNESS toxins,
parasites, low dose organisms
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Algal Toxins
Table 40.3
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TOXINS

• 1. PSP Paralytic Shellfish Poisoning saxitoxin
  - Gonyaulax catenella, Pyrodinium, Gymnodinium
• onset few min to few hrs - neurological symptoms
• close shellfish harvesting to sport/tourists May
  1 to Oct 31
• flushing or deparation not reliable
• 2. Ciguatera algae Gambierdiscus toxicus
• onset hrs - neurological symptoms
• small fish eat algae, bigger fish eat smaller
  fish, problem with larger fish

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• 3. Mycotoxins produced by fungi
• Aflatoxin B - Aspergillus flavus
• Ergot - Claviceps purpurea
• Fumonisins - Fusarium moniliforme (esophogeal
  cancer in humans) assoc. with corn
• Poisonous mushrooms - Amanita

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PARASITES

• 1. Trichinella spiralis
• 2. Taenia saginata, Taenia solium, Cysticercosis,
  Diphyllobothrium latum
• 3. Anasakiasis, nematode worm infection of fish
  increasing because of increase in the sea lion
  population
•  

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LOW DOSE ORGANISMS

• 1. Hepatitis A
• can survive cooking
• 2. Other viruses - Norwalk Virus, Enterovirus
• 3. Salmonella dublin
• 4. Campylobacter jejuni

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CLASSICAL FOOD BORNE ILLNESSmishandling of food
accompanied by an incubation time may be
infection or intoxication
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INFECTION the presence of the organism causes
the illness

• Ingestion of organism
• Growth in host
• Invasion of tissues and/or release of toxins

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• 1. Salmonella - at least 1800 species
• associated with chicken and other meat, eggs,
  dairy
• onset 8 to 48 hrs.
• many people are asymptomatic carriers
• cooking will kill organisms

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• 2. Campylobacter jejuni
• may be the number one cause of food borne illness
• associated with chicken and other meat, dairy
• low dose required (as few as 10 viable cells)
• onset 3 to 5 days (could be 1 to 10)

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• 3. Vibrio cholerae and Vibrio parahaemolyticus
• onset 2 - 3 days
• coast of CA has copepod as reservoir  
• 4. Listeria monocytogenes
• unknown incubation time - few days to 3 weeks 
• 5. Yersinia entercolitica
• onset 16 hrs. to 7 days

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• 6. E. coli 0157H7
• Enterotoxigenic (toxin producing - cholera-like
  toxin)
• Enterohemorrhagic (invasive - "Shiga-like" toxin)
• Dose around 500 cells
• onset 12 - 72 hrs

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INTOXICATION the organism produces a toxin -
the toxin causes the illness

• The organism produces a toxin while the food has
  been mishandled
• The food and toxin are ingested
• The toxin causes the symptoms of the illness

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• 1. Staphylococcus aureus
• has always been the most common food borne
  illness (Campylobacter is new)
• produces a heat stable exotoxin called an
  enterotoxin because it affects the intestinal
  system
• grows well on high protein foods, dairy products,
  meats including ham, can tolerate salt
• cooking or recooking food will not destroy the
  toxin
• onset 1 to 4 hrs to 8 hrs.

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• 2. Clostridium perfringens
• spores found in soil, water, intestinal tract
• associated with high protein foods that are thick
  or slightly anaerobic (gravy, stew)
• requires high dose
• organisms grow and the enterotoxin is produced
  during the sporulation process
• onset 8 to 16 hrs.

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• 3. Clostridium botulinum - botulism
• 7 types toxic to humans, produce a neurotoxin
• associated with alkaline foods under anaerobic
  conditions
• onset 2 hrs to days - neurological symptoms
  (blurred vision, slurred speech, diff.
  swallowing)
• infant botulism associated with lt 1 yr. old
  ingesting honey with endospores that germinate in
  intestines producing toxin 

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• 4. Bacillus cereus
• 2 types Staph-like and Perfringens-like
• emetic illness associated with rice, onset 1 to 6
  hrs.
• diarrheal type associated with more foods, onset
  4 to 16 hrs.
•  

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FOOD HANDLING

• Food must be kept BELOW 40 and ABOVE 140 F and
  not left out for over 4 hrs. 
• Federal standards for shellfish ( lt 230 FC/100g
  and lt500,000 APC/g)  
• Oregon has a standard for hamburger (1,000,000
  FC/100g)