How can you test antimicrobial agents?

the first antibiotic penicillin was discovered by Alexander Fleming in 1928 since then over 100 antibiotic compounds have been discovered and used to save and extend campus lives however inappropriate use coupled with a shortage of newly developed antibiotics means that bacteria have adapted and evolved to find ways to survive the effects of many essential antibiotics this antibiotic resistance is currently considered to be one of the greatest threats to patient safety in the developed world here at the University of Birmingham a number of scientists are conducting research into how antibiotic resistance develops in an effort to tackle this looming global crisis but could any of the experiments that we get shown in our school classrooms play a role in this fight against resistance one experiment we might be familiar with in the classroom is assessing the effects of different plant extracts on the rate of bacterial growth on an agar plate well this same theory could be and still is used by world leading researchers to test how effective certain antibiotics are against different strains of harmful bacteria as a test how effective our antibiotics are we’re going to use a disc assay where we soak small discs of sterile filter paper in different concentrations of antibiotics and then see what effect these discs have on the rate of bacterial growth on an agar plate that’s been seeded with a thin layer of e.coli to prevent other microorganisms or bacteria from colonizing my agar plate I’m going to adopt an aseptic technique so for this my lab bench is spotlessly clean and I’ve got a Bunsen burner to draw air currents upwards and away from my sterile petri dish we’re going to be testing the susceptibility of our bacteria to different concentrations of the antibiotic ampicillin I’ve made serial dilutions to give solutions at five milligrams per mil and 0.5 milligrams per mil to make the 0.5 milligrams per mil solution all I need to do is take one volume of the five milligram per mil solution and add it to nine volumes of water I’m going to add a small volume of each antibiotic solution to a small sterile disc of filter paper I need to ensure that I add the same volume of each solution to reduce variability I’m also going to include a control disk to which I’m just going to add water once the antibiotic has been absorbed and dried onto the disks of filter paper I can then add them to the sterile plate once our disks have been added we can incubate our plate overnight at 37 degrees C and see if there’s been an effect on bacterial growth and so here we have our agar plate that’s been incubated overnight and we can see around our antibiotic discs that we have clear zones of inhibition where bacterial growth has been inhibited by the action of the antibiotic the disc with the highest concentration of antibiotic has the biggest zone of inhibition and the disc with the second highest concentration has a smaller zone of inhibition our control disc has no zone of inhibition now if I compare this plate to a plate that’s been streaked with a strain of bacteria that is resistant to ampicillin we can clearly see that there are no zones of inhibition around any of the antibiotic discs with the increasing prevalence of antibiotic resistant bacteria like these it’s imperative that researchers find out how these bacteria develop this resistance so that we can develop new treatments against bacterial infections and stay one step ahead of resistance you

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