Introduction to food microbiology

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Feb 20, 2013 (4 years and 6 months ago)

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Introduction to food
microbiology

A brief history

Topics in food microbiology

Survey of microbes

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


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
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content/blogs.dir/460/files/2012/04/i
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Kochs_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 19
th

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

emc.maricopa.edu

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 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)

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 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!