Give me Five!
(Two 45 minute periods)
Purpose:
The purpose of this lab is to show students to the amount of bacteria that is collected on their hands in any given day and why the simple act of hand washing on a daily basis can prevent disease. Students will culture their hands after hand washing at the beginning of the day then at the end of the day (with no hand washing in between) Students will also ‘rinse’ their hands in water (no soap) at the end of the day and then culture the water after five, 10, 15 and 20 minutes of boiling.
Background:
Bacteria are everywhere and are spread easily through hand to hand contact. While most bacteria encountered each day tend to be saprophytic or innocuous, there is a group of bacteria that can and do cause disease in those who ingest these bacteria or allow the bacteria access to the eyes or nasal cavities. Our bodies also work hard to protect from disease; our skin is a natural barrier with a normal flora of bacteria there to play competition with the virulent ones, antibodies in our saliva and our tonsils are the first immune line of defense orally. Stomach acid and white blood cells also jump into the fight. While all these defenses work, they don’t work all the time. Bacteria with capsules, endospores or can handle stomach acid will infect and cause disease.
While antibiotics will (in most cases) help the body fight the virulent bacteria, it is better just to not let the bacteria take hold in the first place. Today we have public policies in place to protect our health and one of the most basic is hand washing. One of the questions we are pursuing today is “Just how useful is hand washing with soap through the day?” The other question we will investigate is “Does boiling water kill bacteria”?
Railroad workers in Duffy’s Cut ended up dying from Cholera. Would sanitary practices such as boiling water or washing hands helped stop the spread of disease in the Duffy’s Cut camp? Just to note; not ALL bacteria are killed by boiling water; bacteria that form endospores (Clostridium for example) would survive boiling at atmospheric pressure but for this lab we will just boil water.
Materials:
Petri dishes with nutrient agar (you can get a kit from Carolina Biologicals); assume six per group of students OR divide the dishes into halves or fourths to save money per group.
Sterile swabs and a beaker of sterile water
Beakers for boiling water
Hot plates
37 degree C Incubator (not necessary; most bacteria will grow at room temperature)
Disposable gloves
Methods:
Have students come into the room first thing in the morning and send them to wash their hands. (You can supply the same soap for all students to wash with for consistency). Have each student group take a sterile swab, wet it with the sterile water and then swab it across the palm. Students then will inoculate a petri dish, label the dish and place in the incubator.
Students are then told to NOT WASH THEIR HANDS ALL DAY. They are allowed to wear disposable gloves for lunch for hygiene reasons.
At the end of the day, students will come back to the classroom and the group will take a sterile swab, wet it with the sterile water and then swab it across the palm. Students then will inoculate a petri dish, label the dish and place in the incubator.
One student will ‘rinse’ his hands in sterile water (NO SOAP!) and a swab taken for culture from that water. The water is then heated to boiling and swabs are taken at five, 10, 15 and 20 minutes of boiling and petri dishes are inoculated accordingly, labeled and placed in an incubator.
After 48 hours, students will pull the plates (TAPED FOR SAFETY) and count the colonies on each plate and record this data in a lab notebook.
Assessment:
Students will then do a research paper (based on MLA format) about their findings and conclusion as to what they discovered. This will also include a reflection on their findings.
1