Since the start of the pandemic we've heard a lot about cleaning our hands, but
which works best? Soap or hand sanitizer? Both are helpful, right? But there's more to it than just
applying a chemical. Sure the detergent helps to remove grease and bacterial matter from your skin,
and sanitizer - it's designed to kill microbes. But the physical force of rubbing your hands
together helps loosen dirt too. So it's when you combine all of these - the chemical and the physical -
that you get the best results. In today's lab, we're going to see how disinfectants and detergents can
be used together to eliminate microbes. Always make sure to wear your PPE - lab coat, gloves, and safety
glasses. We've lined this workbench with four laminated squares and labeled them A through D.
We've coated each square with a harmless strain of E. coli. That means that each square has living
bacteria on it right now. You'll need one TSA plate for each square. Label the first plate 'baseline.' The
second 'disinfectant only.' The third 'detergent only,' and the fourth plate 'detergent and disinfectant.'
Square A is our baseline so we're not going to use anything to clean it. Square B is disinfectant only.
Spray the surface with 70 isopropyl alcohol and wait for a few minutes for it to dry. Square C is
detergent only. Use a low shedding wiper to cover the square with a 2% detergent solution.
Wait for two minutes, and then wipe it dry. On Square D, we're going to use both a detergent
and a disinfectant. First, wipe the surface with the 2% detergent solution.
Wait two minutes, and then wipe it dry. Now spray the 70% isopropyl alcohol and wait for
it to dry. Next, we need to collect samples from each square to see if any microbes are present /
Dip a swab into a vial of sterile water and squeeze the excess water by pressing the swab
against the inside of the vial. Start at the top left corner of square and rub the swab across the
square to the bottom right corner - turning the swab as you go and avoid touching the tape.
Open the TSA plate labeled baseline and rub the swab evenly across the entire surface.
Then close the plate and discard the swab in the biohazard trash container.
Take a new swab, and just like we did before, start at the top left corner and work your way down to
the bottom right of the other squares. Inoculate the corresponding plates - always discarding the
swabs in a biohazard container after each use. Stack the plates together and wrap them with tape.
Incubate the samples for at least 36 hours at 32 to 37 degrees celsius. Let's take a look at the
results. Plate A, our baseline, is completely covered in bacteria of course since we didn't do anything
to treat it. Plate B - the one we used disinfectant on - looks pretty clear. That's a vast improvement.
On Plate C, we used just detergent. Well it didn't do so hot. It doesn't look much better
than our baseline. But take a look at Plate D - the combination of detergent and disinfectant was
most effective at killing the E. coli. Our plate is completely clear of bacteria. We can conclude that
the disinfectant is more effective at killing E. coli than the detergent alone, but using both is
still the best option. I want us to try this experiment again, but this time we'll use a
tougher microbe - one that's much harder to kill and harder to say...bacillus theringensis spores.
They're nasty little buggers. They're so nasty that we'll need to fight them with
some tougher chemicals. We've lined this workbench with four new laminated squares
and labeled them E through H. Each square has been treated with the BT
spores, and just like before we need one TSA plate for each square. Label the first plate
baseline, the second disinfectant, label the third hydrogen peroxide, and the fourth plate bleach.
Which do you think will be most effective at killing the spores? Disinfectant, peroxide or bleach?
Let's find out. Use a swab to take a sample of Square E and inoculate the baseline plate. Lightly
spray Square F with 70% isopropyl alcohol. Use a low shedding wiper to evenly spread the alcohol.
Set a timer for four minutes. Spray Square F again with the alcohol and wait four more minutes.
Use a swab to collect a sample and transfer it to the plate labeled disinfectant.
Lightly spray Square G with hydrogen peroxide, and wipe the square down to apply it evenly.
Wait four minutes for it to dry. Apply more peroxide, and wait four more minutes. Use a
swab to transfer a sample from Square G to the plate labeled hydrogen peroxide only.
Lightly spray Square H with five percent bleach. Wait four minutes. Apply more bleach,
and wait four more minutes. Use a swab to transfer sample of Square J to the plate you labeled bleach.
Stack and tape the plates together and incubate them for at least 36 hours at 32 to 37 degrees
celsius. Take a look at these results. The isopropyl alcohol disinfectant, which worked wonders against
the E. coli earlier, did absolutely nothing to stop the spores. The hydrogen peroxide did the trick. It
completely annihilated the spores. And the bleach did pretty well too, but we do have one colony
growing. There isn't a one size one-size-fits-all when it comes to decontaminating microbes. You have
to know the right combination of disinfectants, detergents and physical force to get the job done
right. So how do you know which products to use? Follow the standard operating procedures or SOPs.
Each piece of equipment and manufacturing process has a specific cleaning procedure,
and it's up to you to keep our products free from contamination. Thanks for watching.