Microbiology 101

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Microbiology 101

• Nina G. Parkinson
• October 30, 2007

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Microorganisms

• Bacteria
• Clostridium botulinum, E. coli 0157H7,
• Listeria monocytogenes
• Lactic acid bacteria
• Yeast
• Saccharomyces cerevisiae
• Mold
• Penicillium, Aspergillus
• Parasites
• Cryptosporidium, Cyclospora
• Viruses
• Hepatitis, Norwalk or Noro Virus, AIDS

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Harmful/Harmless/Helpful

• Spoilage
• Public Health
• Economic

• Used to make certain foods

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Bacteria

• Single celled organisms
• Various shapes
• Bacillus (Bacilli) - rod shaped bacteria
• Coccus (Cocci) - round-shaped bacteria
• Vibrio - s or comma-shaped bacteria
• Spirilli - spiral-shaped bacteria
• Filamentous - bacteria that are long and thin

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Bacteria - Characteristics

• Size
• typically 1/25,000 inch
• Motility
• Gram stain
• Spores
• dormant or resting state of bacterial cell
• resistant to heat and disinfectants
• formed when conditions are unfavorable
• reverts back to vegetative state when favorable

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Types of Foodborne Disease

• Infections - ingest organism
• Intoxications - ingest toxins
• naturally occurring (poisonous mushrooms)
• metabolic products of certain bacteria (C.
  botulinum or S. aureus)

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Bacteria - Physiology

• Cell wall
• Food goes in
• Waste materials go out
• Enzymes go out
• Cytoplasm
• Liquid material
• Nucleus
• Genetic information

Cytoplasm
Waste Materials
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Bacteria - Reproduction
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Bacteria - Growth Needs

• Food
• Energy - sugars, carbohydrates
• Nitrogen - protein
• Minerals
• Vitamins
• Water / Moisture
• Temperature
• Oxygen

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Beneficial products

• Pickles
• Yogurt, buttermilk, cheese
• Sausages

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Main Bacterial Pathogens

• Gram negative rods
• E. coli (pathogenic types)
• Salmonella spp.
• Gram positive rods
• Listeria monocytogenes
• Staphylococcus aureus
• Gram positive spore-formers
• Clostridium botulinum
• Clostridium perfringens

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Escherichia coli (pathogenic types)

• Non-sporeformer
• Killed by mild heat
• Aerobic/Anaerobic
• Temp range 7-40C

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Escherichia coli (pathogenic types)

• Sources
• Intestinal tract of humans and animals
• Infected persons are often asymptomatic
• Usually fecal contamination of food or water
• Cross contamination
• Person-to-person spread has been demonstrated
• Poor handwashing in day care and nursery after
  patient contact has contributed to spread

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Escherichia coli (pathogenic types)

• Illness
• Gastroenteritis
• Diarrhea may be bloody, fever
• Strains that cause diarrhea may be invasive,
  enteropathogenic or enterotoxigenic
• Incubation period is 12 to 72 h

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E. coli 0157H7

• Illness symptoms
• Hemorrhagic colitis, severe abdominal cramps
  followed by bloody diarrhea, vomiting, nausea and
  low-grade fever
• May develop into hemolytic uremic syndrome (HUS)
  in children (kidney failure), symptoms appear 3-4
  d after food ingestion

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Salmonella spp.

• Non-sporeformer
• Killed by mild heat
• Aerobic/Anaerobic
• Temp range 5-47C
• Over 2000 serovars known

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Salmonella spp.

• Sources
• Intestinal tract of domestic and wild animals and
  humans
• Ingestion of the organism in food from infected
  animals or contaminated by the feces of an
  infected animal or person. Includes raw eggs,
  raw milk, meat and poultry.

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Salmonella spp.

• Illness
• Salmonellosis
• Acute gastroenteritis sudden onset of headache,
  abdominal pain, diarrhea, nausea and vomiting.
  Fever. Dehydration.
• Incubation period is 6-72 h

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Listeria monocytogenes

• Non-sporeformer
• Killed by pasteurization
• Aerobic/Anaerobic
• Can grow at refrigeration temperatures
• Survives freezing/thawing

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Listeria monocytogenes

• Sources
• Infected domestic and wild animals, fowl and
  humans
• Found in water and mud
• Assume milk, agricultural commodities
  contaminated and plant environments
• Associated with the consumption of contaminated
  vegetables and dairy products

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Listeria monocytogenes

• Illness
• Listeriosis
• Sudden fever, intense headache, nausea, vomiting,
  delirium and coma
• In neonates, transmitted from mother to fetus,
  may cause abortion
• Incubation periods is unknown, likely 3 days to
  several weeks

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Staphylococcus aureus

• Non-sporeformer
• Killed by mild heat
• Enterotoxin is heat stable
• Aerobic/Anaerobic
• Temp. range 7-45C

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Staphylococcus aureus

• Sources
• Usually humans, organism harbored in nasal
  passages and on skin
• Occasionally from cows with infected udders
• Microbe multiplies in inadequately stored foods,
  producing heat-stable enterotoxin
• Illness occurs when toxin is consumed
• Food handler commonly contaminate foods

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Staphylococcus aureus

• Illness
• Staphylococcal food poisoning
• An intoxication of abrupt onset characterized by
  severe nausea, cramps and vomiting
• Often accompanied by diarrhea
• Duration of illness 1-2 days
• Onset of symptoms 1-6 hours

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Clostridium botulinum

• Sporeforming
• Spores are heat resistant
• Anaerobic
• Growth in pH gt4.6

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Clostridium botulinum

• Sources
• Soils, marine sediment, intestinal tract of
  animals, including fish
• Vegetables and grains contain spores
• Toxin must be ingested to cause disease
• Spores must germinate and grow to vegetative
  cells to produce toxin

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Clostridium botulinum

• Illness
• Botulism
• Severe intoxication from ingestion of toxin
• Blurred or double vision, dry mouth, difficulty
  swallowing, paralysis or respiratory muscles
• Onset 12-36 hrs

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Clostridium perfringens

• Sporeforming
• Anaerobic/Sl. aerobic
• Temp range 12-50C

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Clostridium perfringens

• Sources
• Soil, intestinal tract of healthy persons and
  animals (cattle, pigs, poultry, fish)
• Ingestion of contaminated food, held under
  conditions allowing growth of organisms
• Usually inadequately heated or reheated meats,
  stews or gravies
• Enterotoxin is produced in the gut resulting in
  symptoms

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Clostridium perfringens

• Illness
• Perfringens food poisoning
• Gastroenteritis characterized by diarrhea and
  nausea. Vomiting and fever are usually absent.
• Duration of 1 day
• Incubation from 6-24 hours

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Yeast

• Small, single-celled plants
• but bigger than bacterial cells
• Members of fungi family
• Round or oval shape
• Examples
• Saccharomyces cerevisiae
• Rhodotorula

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Yeast

• Reproduce by
• budding
• binary fission
• spores

Budding
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Yeast Growth or dietary needs

• Temperature
• pH
• Water activity
• Dietary needs
• sugar starch

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Yeast - Waste products
AND/OR STARCH
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Yeasts - Spoilage
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Molds

• Members of fungi family
• Multi-cellular
• rhizome grows, looks for nutrients
• reproductive cells or spores grow and attach to
  food source
• Grow easily (moisture and air) at most
  temperatures

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Molds

• Heat resistant
• Byssochlamys fulva
• Aspergillus flavus
• Not heat resistant
• Penicillium roqueforti
• Indications of poor sanitation
• Geotrichum

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Molds are used to make certain favorable products

• Cheeses (Roquefort and Blue)
• Soy Sauce
• Chemicals
• Citric acid
• Lactic acid
• Enzymes
• Antibiotics

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Molds - Problems

• Mycotoxins produced by certain molds growing
  in specific foods
• Patulin in apples
• Aflatoxins in peanuts
• Carcinogens, poisons

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Parasites

• An organism that lives in or on and at the
  expense of another (the host)
• Cryptosporidium
• salad, raw milk, chicken salad, apple cider
• Cyclospora
• raspberries, basil, lettuce
• Giardia
• water
• Sensitive to extreme temperatures
• Control measures
• Use of non-contaminated waters
• Hygienic practices

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Parasites

• Cyclospora
• Cryptosporidium

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Parasites

• Sensitive to extreme temperatures
• Control measures
• Use of non-contaminated waters
• Hygienic practices

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Viruses

• Submicroscopic infectious agent composed of
  nucleic acid and protein obligately parasitic
  and hence replicates only within a living host
  cell
• Hepatitis A
• Norwalk Virus
• Transmission by infected food handlers

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Controlling Microorganisms in Foods

• Control of moisture
• Preservatives
• Low temperature
• Refrigeration
• Freezing
• High temperature
• Pasteurization
• Canning
• Others

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Controlling Microorganisms in the Plant

• Sanitation
• Improper storage/holding temps
• Inadequate cooking
• Poor personal hygiene
• Cross-contamination
• Improper reheating
• Poor storage practices

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Growth Needs - Bacteria (similar for yeast and
molds)

• Temperature
• Oxygen
• aerobes
• anaerobes
• facultative anaerobes
• Water activity
• amount of water available for growth
• pH
• level of acidity

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Controlling Microorganisms

• Once we know what they need to grow, we can
  control them

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Controlling Microorganisms

• Temperature
• Thermal process
• canning
• pasteurization
• Freezing
• Refrigeration

YUMMY
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Controlling Microorganisms

• pH or level of acidity
• pH scale
• 1 (acid)
• 7 (neutral)
• 14 (basic/alkali)

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Controlling Microorganisms

• Water Activity (Aw) - availability of water for
  microorganisms not the amount of moisture in a
  food
• Scale from 0 to 1
• Most foods are above 0.90 (fruits, vegetables,
  meats, bread, cheese, etc)
• Dry foods or foods high in sugar or salt can have
  Aw 0.50 (noodles) to 0.80 (jams/jellies)

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Controlling Microorganisms

• Oxygen
• aerobes (grow with oxygen)
• anaerobes (grow without oxygen)
• facultative (grow with or without oxygen)
• Modified Atmosphere Packaging (MAP)

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Controlling Microorganisms

• Preservatives
• chemicals that inhibit microbial growth
• sodium benzoate
• potassium sorbate

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Controlling Microorganisms

• Eliminating the source of the contamination
• Incoming materials
• Environment
• Equipment
• Employees
• ... SANITATION

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SANITATION

• Incoming materials

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SANITATION

• Environment

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SANITATION

• Equipment

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SANITATION

• Equipment

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SANITATION

• Equipment

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SANITATION

• Employees

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SANITATION

• Employees

EMPLOYEES MUST WASH HANDS--- BEFORE ---
RESUMING WORK
NOTICE
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Testing for Microorganisms

• Inspections
• Counts
• Presence/Absence Tests
• Rapid methods

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Bioluminescence procedures
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How contamination happens

• 1 gram of fecal material might contain 1 million
  cells of E. coli 0157H7
• 1 gram fecal material spread evenly over 1,000 to
  100,000 pieces of produce
• 10 to 1,000 cells per piece of produce
• 1,000 to 100,000 potentially infectious pieces of
  produce