8/13/2019 Whats On My Skin

1/14

8/13/2019 Whats On My Skin

2/14

According to Nathan Wolfe, microbiologist

at Stanford University, the microbes in your

body outnumber your own cells by ten toone and can weigh as much as or more

than your brainabout three pounds in an

average adult.

8/13/2019 Whats On My Skin

3/14

For the most part, the microbes inhabiting

our bodies are either beneficial ones or

unobtrusive freeloaders. They help us digest

our food, absorb nutrients, and manufacture

vitamins. They also train our immune

systems to combat infectious intruders.

Bacteria living on our skin secrete a natural

moisturizer, preventing cracks that could

allow pathogens to penetrate.

8/13/2019 Whats On My Skin

4/14

If the idea of microbes living on your skin

makes you want to go home and take a

shower, consider this advice from

researcher Julia Serge, "We should think

about proper sanitation with the skin, but

not sterilization. There are good bacteria

that really promote healthy skin."

8/13/2019 Whats On My Skin

5/14

Life On Our Skin

What lives on our skin? In this video segment

from Science Friday, Dr. Martin Blaser, the

chairman of the department of medicine at

New York University (NYU) School of Medicine,

is trying to find out. After swabbing the arms

of six people, Blaser and his lab found 182

different species of bacteria--thirty of whichhad never been seen before.

http://aptv.pbslearningmedia.org/resource/sf10.sci.lsci.living.lifeskin/life-on-our-skin/http://aptv.pbslearningmedia.org/resource/sf10.sci.lsci.living.lifeskin/life-on-our-skin/

8/13/2019 Whats On My Skin

6/14

Predictions

On which area of skin on your body do you

think you will find the most bacteria?

The least bacteria?

Why would one skin area have more bacteriathan another area?

8/13/2019 Whats On My Skin

7/14

Materials

Agar prepared Petri dishes

Agar: a gelatinous substance (usually

derived from seaweed extract) used as a

nutrient for growing microorganisms.

Cotton swabs

Latex gloves Distilled water

8/13/2019 Whats On My Skin

8/14

Vocabulary

Bacterial Culture: the growing of bacteria ina nutrient substance in specially controlledconditions for scientific, medical or

commercial purposes

Colonymillions of bacterial cells grouped

together that can be observed with thenaked eye

Under favorable conditions, bacteria can

multiply rapidly and form a colony.

8/13/2019 Whats On My Skin

9/14

Whats Happening?

Bacteria are single-celled microorganisms that canonly be seen through a microscope. There are many

different kinds of bacteria, and they are found

everywhere, in almost any type of environment,including extreme environments like hot springs.

8/13/2019 Whats On My Skin

10/14

Whats Happening?

Just like any other organism, bacteria neednutrients to survive. The agar in the Petri dish is

composed of nutrients usually derived fromseaweed extract and other possible components,

depending on the source. The nutrients areconverted into energy and used to help the

bacterium grow and reproduce. Under favorableconditions, a single cell can turn into millions of

cells within a few hours, and into a billion cellswithin a few days. The grouping of millions ofbacterial cells is called a colony. Often a colony can

be seen without a microscope.

8/13/2019 Whats On My Skin

11/14

Whats Happening: Phases of

Bacterial Growth

1. LAG PHASE: Bacteria are adapting to a new environment.The number of cells does not change during this time.

2. EXPONENTIAL PHASE of growth: Binary division occurs. The

number of cells doubles approximately every 20 minutes.

3. STATIONARY PHASE: The number of bacteria remains nearlyconstant, because the dividing rate = the rate of cell death.Cells begin to die due to the build up of waste and thedepletion of nutrients.

4. DEATH or DECLINE PHASE: The death rate is greater than thedividing rate, and the number of cells decreases.

8/13/2019 Whats On My Skin

12/14

Whats Happening: Phases of

Bacterial Growth

Stationary

Phase

Number Exponential Death Phase

of Cells Phase

Lag Phase

Time

8/13/2019 Whats On My Skin

13/14

Whats Happening?

Samples collected from human skin may contain

other types of microorganisms. Most bacteria

have one of three basic shapesrod, spherical,

or spiral. Colonies that exhibit fuzzy hair-like

growth are most likely fungus or mold.

8/13/2019 Whats On My Skin

14/14

Topics for Discussion

What variables could have caused different

types of bacteria to grow?

Why do you think that bacteria can become

resistant to antibiotics or antibacterial agents

such as household cleaners?

How do bacteria reproduce?

Why would scientists want to grow and study

bacteria?