Food Microbiology:

Delicious or…Boehm 2010

…Dangerous?

Presentation by: Ms. Boehm, Wellesley High School, MA

Boehm 2010

Introduction to Food Microbiology

Objectives:•Provide a general introduction to microbiology•Introduce the concept that microbes are found

in the food that we eat every day•The microbes can be helpful in producing

some types of delicious food•The microbes can also be harmful, as in the example of the E. coli spinach contamination

•Explain methods of food sterilization to preventcontamination in the future.

Boehm 2010

General Introduction to Bacteria

Fun Facts about Bacteria

Necessary to make many everyday foods includingyogurt, cheese, sauerkraut, soy sauce, vinegar

Used to clean up various forms of pollution including oil spills, pesticides, sewage

Produce antibiotics that we can use to the fight bacteria that make us sick

Produce Botox so we can all have wrinkle-free foreheads

Fun Fact: Bacteria comprise about 1/20th of your total body weight!

•Bacteria are the most abundant organisms on earth.

•Of the three major domains of classification, bacteria take up two.

Classification of Bacteria

•The domain Bacteria is often referred to as eubacteria•The most common type of bacteria found on earth•Examples: Streptococcus, Escherichia coli, Clostridium botulinum, Salmonella

•The domain Archaea is often referred to as archaebacteria•Archaea are thought to resemble the very first cells on earth•They are more rare and live in extreme conditions

Identification of Bacteria

•Bacteria have three basic shapes.•These images are magnified by more than 10,000 times!

•They are all surrounded by some type of cell wall

Sphere shaped:coccus

Rod shaped:bacillus

Spiral shaped:spirochete

Bacterial Shapes

Staining BacteriaGram-positiveGram-positiveGram-negative:Gram-negative:

Thick peptidoglycan layerThick peptidoglycan layer holds purple dyeholds purple dye

Double membrane doesn’t Double membrane doesn’t hold purple dyehold purple dye

Peptidoglycan

Plasma Membrane

Gram-Negative Gram-Positive

Plasma MembranePeptidoglycan

OuterMembrane

Holds Purple DyeWill Not Hold Purple Dye

DNA

Cell Wall Structure

The Genetics of Bacteria

•The main DNA is a long circular loop, one single chromosome, not contained within a nucleus•Many bacteria also contain plasmids, a smaller loop of DNA•It is the plasmid that allows these asexual organisms to have variation, and can also make the bacteria pathogenic!

Bacteria Are Prokaryotic

Bacterial Conjugation

Often it is the plasmid that contains genes that are pathogenic to humans!

Bacterial Growth and Division

Bacterial Growth and Division

• Most bacteria divide every 20 minutes• They will form bacterial colonies

•Bacteria divide by a process called prokaryotic fission•The product from one bacterium dividing would be two genetically identical daughter cells

Good vs. Bad Bacteria• There are many different kinds of bacteria, most of

which will not make you sick and may actually help you:– Staphylococcus epidermidis lives harmlessly on your skin

– Escherichia play a nutritional role in the intestinal tract by synthesizing vitamins, especially vitamin K.

– Neisseria subflava lives harmlessly in most people’s mouths

• Fun Fact: The human body contains 20 times more microbes than it does cells!

• But, there are also some that can make you sick…

•Strep Throat - Streptococcus pyogenes

•Ear Infections - Streptococcus pneumonia, Haemophilus influenzae, Moraxella catarrhalis

•Meningitis – Neisseria meningitidis, Haemophilus influenzae

•Tuberculosis – Mycobacterium avium, M. tuberculosis

•Gonorrhea – Neisseria gonorrhoeae

•Syphilis – Treponema pallidum

Bacteria Can Cause Many Different Illnesses

Food Microbiology

Delicious or Dangerous?

Food Microbiology• Microorganisms are a part of the food we eat every

day, specifically bacteria

• Most of these bacteria are harmless, non-pathogenic

• BUT some of these bacteria are harmful to us, pathogenic

• Is the food “delicious or dangerous????”

Delicious Food Microbiology

• Yogurt has bacteria added to it that give it a slightly sour taste– “active yogurt cultures”– Lactobacillus bulgaricus and Bifidobacteria

• Cheeses can be fermented with various bacteria– Swiss cheese -Propionibacterium – Blue cheese -Penicillium roqueforti and Lactobacillus

• Finally, many pickled vegetables get their flavor from bacteria– Sauerkraut – Leuconostoc and Lactobacillus– Pickles – Lactic acid bacteria

Dangerous Food MicrobiologyContaminated Food Can Make You Sick

Escherichia coli O157:H7*Source: spinach, ground beef, frozen pizza **Symptoms: vomiting, diarrhea (often bloody)

Clostridium botulinum -botulism*Source: soil, water, non-acid canned foods*Symptoms: flaccid paralysis and possible death (or a smooth face)

Salmonella typhimurium – salmonella*Source: eggs, chicken meat, dairy products*Symptoms: headache, chills, vomiting, diarrhea

Facts about Foodborne Illness

• “The CDC estimates that 76 million people get sick, more than 300,000 are hospitalized, and 5,000 Americans die each year from foodborne illness.”

• Uncooked foods are the largest source of foodborne illness in the US (raw meat, uncooked eggs, raw vegetables, etc.)

Case StudyOutbreak of E. coli in

Spinach, 2006

What happened?• There are rare cases of E. coli 0157:H7 contamination each year

• In late August of 2006, the CDC noticed a dramatic spike in cases

• The hypothesis was that this was a foodborne illness, but the source was unknown

Who was affected?• E. coli O157:H7 outbreak resulted in 205 confirmed illnesses and three deaths

• The contaminated spinach was found in 26 states.

Source traced to spinach

• The CDC narrowed the source down to fresh spinach coming from an isolated farm in southern California– Normally fresh vegetables do not harbor pathogenic bacteria

• The CDC, in September 2006, reported an apparent outbreak of E. coli O157:H7 linked to the consumption of bagged spinach

How did the spinach get contaminated?

• Environmental risk factors for E. coli O157:H7 contamination at or near the spinach field:– the presence of wild pigs in the proximity of irrigation wells used to grow produce for ready-to-eat packaging

– surface waterways exposed to feces from cattle and wildlife

• The strain of E. coli is normally found in the intestinal tract of cows, pigs and deer.

How did the CDC identify E. coli 0157:H7?

•The CDC cultured the bacteria from the spinach and placed it on a food source E. coli likes to eat, such as EMB (eosin methylene blue) agar

•E. coli grows pink colonies on EMB agar•No other bacteria will grow pink on this media.

•The CDC was able to distinguish the E. coli 0157:H7 strain from other E. coli strains by doing gel electrophoresis of the DNA.

•The genetic fingerprint will be different- do you know why?

How could our class identify E. coli?

• 3 methods of potential identification methods:1. Look at shape under the

microscope2. Gram staining3. EMB agar

1. 2. 3.

Symptoms of E. coli 0157:H7 infection

• Type of enterohemorrhagic Escherichia coli (EHEC)

– Hemorrhagic (bloody) diarrhea

– Abdominal pain

– Kidney failure

How does E. coli 0157:H7 make you sick?

• E. coli 0157:H7 produces a toxin, verotoxin, similar to a shiga toxin

• Verotoxin invades the cells of the intestine and inhibits protein synthesis

– Inhibition of protein synthesis = cell death

How can we avoid getting sick?

• Cook the food

– E. coli 0157:H7 (on spinach) can be killed by cooking at 160° F for 15 seconds

– Cook meat until grey/brown in color and juices run clear to kill bacteria

How can food contamination be prevented pre-consumer?• Irradiation is one possible solution– Process of irradiating foods with ionizing radiation (gamma rays or high energy electrons) to destroy microorganisms contaminating the food

– According to CDC, irradiation does NOT change nutritional value, composition of the food, or make the food dangerous

• Cool fact: astronauts eat irradiated food in space!

Summary• Bacteria are the most abundant organisms on earth

• Some bacteria never cause us harm and can be helpful to us (non-pathogenic)

• Some bacteria are harmful to us (pathogenic)– Toxins produced by bacteria can damage our cells– Outbreak of E. coli 0157:H7 in spinach

• Contamination and infection can be prevented by a variety of methods– Cooking – you can do at home– Irradiation – can be done by producers