INTRODUCTION TO FOOD MICROBIOLOGY
PEOPLE HAVE “PRACTICED” FOOD
MICROBIOLOGY FOR THOUSANDS OF
YEARS
Even if they didn’t k
know it
HISTORY OF FOOD MICROBIOLOGY
•
8-10,000 years ago
–
•
Ca. 4,000 years ago
–
•
Fermented foods
1600s
–
•
Food preservation
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/wpcontent/blogs.dir/460/files/2012/04/i-67928b6ba62e66dd3d1e18842c3e71d7Kochs_postulates.gif
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”

PROKARYOTES
•
•
•
•
Smaller cells
No nucleus or organelles
Single-celled
Bacteria and archaea
EUKARYOTES




•
Larger cells
Cells have nucleus and
organelles
Can be single-celled or
multicellular
Plantae, Animalia, Fungi,
Protista
Viruses and prions are not
cells so are not considered
alive
PROKARYOTES VS EUKARYOTES
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
Can cause disease
Interfere with food processing
T4-infects E. coli
Hepatitis A- infects humans
PROTOZOANS, ALGAE, HELMINTHS
Protozoans can cause parasitic disease
(Giardia, Cryptosporidium, Toxoplasma)
 Algae- photosynthetic protists

 Contaminants,

food products, toxins
Helminths- parasites
 Roundworms,
tapeworms- contaminated food
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
Morphology
www.zazzle.com
Scienceblogs.com
BACTERIAL CLASSIFICATION, CONTINUED
Aerobes, anaerobes, fermenters
 Spore formers, non spore formers
 What metabolic products do they produce?



What do they use for food?


Acids, alcohols, gases- and which ones?
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
progress!
