Antibiotics and Bacteria petri dishes 20171218 20180111

Antibiotics and Bacteria   petri dishes   20171218   20180111


In this presentation, I’m going to talk to you about how we can view the effects of different antibiotics on bacterial growth. So to begin this procedure we need petri dishes and those petri dishes are filled with an agar, a jello like substance, which contains nutrients. The next step is to cover the petri dish with a sample of bacteria. So the way we would do that Is we would get a sample of our bacterium on a swab and we would swab over the agar And kind of try and cover that with bacteria. And if you have taken, or will take, microbiology There’s a particular way that you cover the petri dish with a colony of bacteria. So We kind of swab the petri dish or the agar go with that bacterial sample So the idea is to cover the area and allow that bacteria to grow and kind of fill in all of these spaces. So what the purpose of this experiment is to see how this bacterial growth is going to be affected by different antibiotics. So we have a single species of bacteria that we’ve covered the petri dish with and then the next step is to add some antibiotic discs. Basically the antibiotic discs pieces of paper that have been soaked in an antibiotic and so in this experiment what we did was add four antibiotic discs and they stick to the petri dish so each of these four circles represents a different antibiotic and then what we do is place this petri dish with those antibiotic discs in an incubator for 24 to 48 hours and allow that bacteria to grow. So what I’m going to show you next are the results of those petri dishes. So this first petri dish shows how Staphylococcus epidermidis grew in the presence of these four different antibiotic discs. So here you can see the bacterial growth, it’s this kind of tan-colored sweeping marks all over the agar and then each of these discs again is a different kind of antibiotic What we would do is, for example down here, you can see this CIP 5 That’s an abbreviation for ciprofloxacin which is a kind of antibiotic and what we would do we would measure the diameter of this dark area right here and this dark area around that antibiotic disk is referred to as the zone of inhibition. So basically we covered the petri dish with bacteria, the bacteria would normally grow all over the place however, if that particular bacterium is affected or inhibited by a particular antibiotic it’s not going to grow in that area where the antibiotic is present. So this is showing us that Staphylococcus epidermidis is susceptible to the antibiotic ciprofloxacin. You can see down here. We have another antibiotic that has a smaller zone of inhibition, but still shows growth inhibition of the Staph epidermidis. These two antibiotics have no zone of inhibition and therefore Staphylococcus epidermidis is unaffected by those two particular antibiotics. So let’s look at another example. This is showing you Bacillus subtilis. So the Bacillus subtilis was spread all over this agar to try and grow And then those same four antibiotic discs were added to the petri dish as the bacteria grew in the incubator. What you can see is that Bacillus subtilis susceptible to all four of these different kinds of antibiotics. So the zone of inhibition is relatively large for each of these four antibiotics that are shown. So here’s the last example, this is showing you E. coli grown in the presence of those same four antibiotics and it’s unaffected by two of these and you can kind of see a faint zone of inhibition with these two antibiotics. So again E. coli is affected by two and unaffected by two. What you’ll notice from these pictures is that different bacteria are affected by different antibiotics and that’s kind of important when we think about treating diseases with antibiotics and and knowing which kind of bacterium an individual has an infection with and therefore knowing which kind of antibiotic should be prescribed to treat that infection

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