Introduction to food microbiology

A brief historyTopics in food microbiology

Survey of microbes

People have “practiced” food microbiology for thousands of years

Even if they didn’t kknow it

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 Koch’s postulateshttp://scienceblogs.com/digitalbio/wp-content/blogs.dir/460/files/2012/04/

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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

Foodborne pathogens

• 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

discovered!

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)

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?

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?

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

“accidental”

Classification of organisms

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Where are viruses and prions?

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,

Protista

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

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

T4-infects E. coli

Can cause diseaseInterfere 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)

humanillnesses.com

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

Major classification criteria

• Gram-positive or Gram-negative

morningsidemicro.wikidot.com

www.zazzle.com Scienceblogs.com

Morphology

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 waterDo 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

progress!