Is it already the end of week 3??
This week I got to work on my Kirby-Baucer plates. Before the advent of miniaturization and computerization of microbial techniques, one of the most common methods used to rapidly determine bacterial sensitivity was resistance to specific antimicrobial drugs was to use small paper disks, each saturated with a specific concentration of these different drugs. In my experiment, these ‘drugs’ were my leachates from nanosilver products and the bacteria was E.coli K12. These Kirby-Baucer plates can be interpreted by its size of the zone of inhibition. The zones are measured in millimeters and the size describes an organism as being susceptible, sensitive, or resistant to a drug.
Right:Kirby-Baucer Plate 
MY EXCITING EXPERIMENT!
STEP 1: Prepare leachates
I had a total of 21 samples. 1mg or 1ml was extracted from each sample and was inserted into a bottle of 100ml of nanopure water which underwent around 24 hours of mixing on the stirring table.
STEP 2: Prepare the E.coli.
The E.coli needs to be at its log phase, which is when it multiplies exponentially, doubly in number every few minutes. From doing O.D measurements and making an exponential graph with excel last week, I learned that the E.coli is in its log phase about 2 hours after being inoculated. The ‘bug’ needs to be used before it reaches stationary phase, which is when the bacteria’s booming growth stops and the number of bacteria stabilizes.
Left: This is about what the exponential growth of E.Coli K12 looks like.
STEP 3: Prepare agar plates /Streak with E.coli/Dip filter paper disk into leachate solution and place it into plate
In this experiment, I used LB agar which I plated previously. So I had 21 samples which to ensure the data, I made triplicates. This is a total of 93 plates! Working under the biological hood, I streaked all the agar plates with E.coli, which was inoculated 2 hours before, and then placed filter paper disks into the center, three disks for each sample.
STEP 4: Para film and store in incubator
So in total, I used:
93 plates
93 swabs
93 sprays of ethanol to clean the forceps which I use to place the filter paper disks
93 filter paper disks
93 strips of parafilm
MANY kimwipes to dry my forceps
Brook, my lab partner, did the same procedures, just with Bacillus, a different bacteria. So that’s even more materials used! While I was doing all this, I just noted to myself how much resources were used due to scientific experiments and research…. All the plates I used cannot even be reused due to sterility issues…Maybe someone should invent an efficient way to conduct experiments!!!
RESULTS
So after 24 hours, I looked at my 93 plates. No big changes could be found from the previous day, other than that the E.Coli had grown into thick colonies. E.coli was resistant to all the ‘drugs’ except for 1mg/L of Silver Nitrate. Christina said that maybe these nanosilver products are scams, but we need to give the plates more time if we want to make a more accurate assumption. So both Brook and my plates were placed into the walk in freezer. It will be in there for a week before we check up on them… until then… :D
PHOTOGALLERY
Christina, Brook, and I examining our plates.
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Kirby-Baucer Plates
Brook, Christina, and I in the cold walk-in-freezer!
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