Introduction to food microbiology
A brief history Topics in food microbiology
Survey of microbes
People have “practiced” food microbiology for thousands of years
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)
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
• 1849 John Snow: cholera spread through water contaminated with feces
• Several waterborne pathogens isolated
More pathogens isolated from food, diseased animals, feces Docsity.com
• Salmonella enteriditis- isolated from meat as well as person who ate it
• Staphylococcus • Clostridium botulinum • Isolated in late 19th century • Koch’s postulates in action!
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
Molecular genetics and biotechnology
• Rapid identification • Genetic engineering • Understanding mechanisms of resistance,
biochemical processes, etc.
Limitations of microbiological techniques
• Most microbes cannot be grown in the laboratory
• Microbes do not grow in isolation • Most microbes have not even been
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)
• Which microbes, and under what conditions? • What are the metabolites (products)? • How do they work in the cold? • How can they be controlled?
• Detection • Identification • Control • How do we monitor and share information? • Are we making the problem worse?
– Antibiotic resistance – Are we introducing pathogens through our
What kinds of microbes are found in food?
• Bacteria • Fungi (yeasts and molds) • Viruses
• Protozoans, algae, helminths to a lesser extent • (Helminths=worms) • Protozoans and helminths are considered
Classification of organisms
Where are viruses and prions? Docsity.com
Prokaryotes vs eukaryotes
prokaryotes • Smaller cells • No nucleus or organelles • Single-celled • Bacteria and archaea
• Viruses and prions are not cells so are not considered alive
eukaryotes • Larger cells • Cells have nucleus and
organelles • Can be single-celled or
multicellular • Plantae, Animalia, Fungi,
• 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
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
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
Viruses infect cells
Hepatitis A- infects humans
Can cause disease Interfere with food processing
Protozoans, algae, helminths
• Protozoans can cause parasitic disease (Giardia, Cryptosporidium, Toxoplasma)
• Algae- photosynthetic protists – Contaminants, food products, toxins
• Helminths- parasites – Roundworms, tapeworms- contaminated food
Life cycle of a tapeworm (helminth)
• 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
Major classification criteria
• Gram-positive or Gram-negative
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?
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