Introduction to food microbiology

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Introduction to food microbiology

• A brief history
• Topics in food microbiology
• Survey of microbes

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People have practiced food microbiology for
thousands of years
Even if they didnt k know it
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History of food microbiology

• 8-10,000 years ago
• Food preservation
• Ca. 4,000 years ago
• Fermented foods
• 1600s
• Early observations with microscopes
• 1700s
• Spontaneous generation was challenged (in
  experiments involving food)

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1800s The Golden Age of Microbiology -Cell
theory -Spontaneous generation disproved -Proof
that fermentation is a biological process -Germ
theory of disease -Canning invented -Discovery
of organisms that cause foodborne
illness -Techniques for studying microbes
Kochs postulateshttp//scienceblogs.com/digitalbi
o/wp-content/blogs.dir/460/files/2012/04/i-67928b6
ba62e66dd3d1e18842c3e71d7-Kochs_postulates.gif
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Sanitation

• 1849 John Snow cholera spread through water
  contaminated with feces
• Several waterborne pathogens isolated

More pathogens isolated from food, diseased
animals, feces
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Foodborne pathogens

• Salmonella enteriditis- isolated from meat as
  well as person who ate it
• Staphylococcus
• Clostridium botulinum
• Isolated in late 19th century
• Kochs postulates in action!

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Techniques in microbiology

• Pure culture technique
• Microscopy
• Staining, esp. Gram stain
• Sterile microbiological media (liquid and solid)
• Aseptic technique
• Methods to control microbial growth
• Biochemical tests to distinguish microbes
• Studying beneficial microbes as well as pathogens

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Molecular genetics and biotechnology

• Rapid identification
• Genetic engineering
• Understanding mechanisms of resistance,
  biochemical processes, etc.

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Limitations of microbiological techniques

• Most microbes cannot be grown in the laboratory
• Microbes do not grow in isolation
• Most microbes have not even been discovered!

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Topics in food microbiology

• Fermentation/probiotics
• Fermented foods and important metabolites
• Making fermenting strains more stable
• Resistant to viruses
• Enhance fermentation capacity
• Understanding probiotics and their effect on the
  body (the microbiome)

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Food spoilage

• Which microbes, and under what conditions?
• What are the metabolites (products)?
• How do they work in the cold?
• How can they be controlled?

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Foodborne pathogens

• Detection
• Identification
• Control
• How do we monitor and share information?
• Are we making the problem worse?
• Antibiotic resistance
• Are we introducing pathogens through our
  processes?

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What kinds of microbes are found in food?

• Bacteria
• Fungi (yeasts and molds)
• Viruses
• Protozoans, algae, helminths to a lesser extent
• (Helminthsworms)
• Protozoans and helminths are considered
  accidental

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Classification of organisms
emc.maricopa.edu
Where are viruses and prions?
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Prokaryotes vs eukaryotes

• prokaryotes

• eukaryotes

• Smaller cells
• No nucleus or organelles
• Single-celled
• Bacteria and archaea
• Viruses and prions are not cells so are not
  considered alive

• Larger cells
• Cells have nucleus and organelles
• Can be single-celled or multicellular
• Plantae, Animalia, Fungi, Protista

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Nomenclature

• Binomial name genus and species
• Ex. Salmonella typhimurium S. typhimurium
• Subspecies
• Lactococcus lactis ssp. lactis, (soft cheese)
• L. lactis ssp. cremoris (hard cheese)
• Serovar, pathovar, biovar

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Yeasts and molds

• Yeasts single-celled eukaryotes
• Molds multicellular structure (filaments,
  spores) required for reproductions
• Can be used to make foods but also involved in
  spoilage

• Saccharomyces cerevisiae
• Carbon dioxide and ethanol

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Molds can grow almost anywhere

• Food spoilage
• Toxins
• Allergens
• Food processing
• Different genera grow on different foods
• Rhizopus- fruits, vegetables, bread
• Geotrichum- dairy mold
• Penicillium-spoils almost everything, but also
  used to make cheese

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Viruses infect cells
Can cause disease Interfere with food processing
T4-infects E. coli
Hepatitis A- infects humans
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Protozoans, algae, helminths

• Protozoans can cause parasitic disease (Giardia,
  Cryptosporidium, Toxoplasma)
• Algae- photosynthetic protists
• Contaminants, food products, toxins
• Helminths- parasites
• Roundworms, tapeworms- contaminated food

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Life cycle of a tapeworm (helminth)
humanillnesses.com
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Bacteria (eubacteria)

• We will spend much lecture time, and most lab
  time, working with them
• Classification is complicated and changing all
  the time
• Most bacterial species have not been described,
  but many have been very well studied

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Major classification criteria

• Gram-positive or Gram-negative

morningsidemicro.wikidot.com
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Morphology
Scienceblogs.com
www.zazzle.com
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Bacterial classification, continued

• Aerobes, anaerobes, fermenters
• Spore formers, non spore formers
• What metabolic products do they produce?
• Acids, alcohols, gases- and which ones?
• What do they use for food?
• Carbohydrates, lipids, proteins
• Under what conditions do they grow?
• Temperature range, pH range, availability of
  water
• Do they cause disease? What kind?

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What should a food microbiologist know?

• Characteristics of the different types of
  microbes
• How to identify and enumerate them
• Factors that affect their growth (innate and
  introduced)
• Fermentation vs spoilage
• How microbes cause disease
• That the field of food microbiology is a work in
  progress!