By: David Toelkes
June 12, 2012
Development of bacterial resistance to the antimicrobial drugs identified the need to determine a given bacterium’s susceptibility or resistance to a given drug which prompted W. M. M. Kirby and A. W. Bauer to develop a single disk method for susceptibility testing. This experiment used the Kirby-Bauer disk diffusion test to measure the degree to which Penicillin, Streptomycin, Ampicillin, and Chloramphenicol inhibited the growth of the bacterium, Proteus vulgaris. The measured zone of resistance for each antibiotic was compared against antibiotic performance standards maintained by the Clinical Laboratory Standards Institute to determine whether Proteus vulgaris was susceptible, intermediate, or resistant to the antibiotics used in the experiment. Proteus vulgaris demonstrated susceptibility to Ampicillin, Streptomycin, and Chloramphenicol but resistance to Penicillin. The average zone of inhibition for Ampicillin measured in this experiment was just 2 mm above the threshold diameter for Proteus vulgaris to be classified as susceptible. Testing on a much broader scope and over an extended period of time would have to be undertaken to determine if Proteus vulgaris is strengthening in resistance to the antibiotics which are currently effective in treating infections caused by Proteus vulgaris.
In 1928, bacteriologist Alexander Fleming made a chance discovery from an already discarded experiment that had become contaminated. The mold that had contaminated his experiment turned out to contain a powerful antibiotic, which Fleming called penicillin, and the age of modern antibiotics was launched. (Cowan, 2012) Even though Alexander Fleming discovered the antibiotic properties of penicillin in 1928, it was not until August 1941 that the first experiments in which penicillin was given to sick persons were published. Between 1941 and 1945, penicillin’s success in treating a broad range of infectious diseases confirmed that the discovery of penicillin was “of the greatest importance for medical science” (Liljestrand, 1945). Alexander Fleming, in his Nobel Prize acceptance speech, warned: Penicillin is to all intents and purposes non-poisonous so there is no need to worry about giving an overdose and poisoning the patient. There may be a danger, though, in underdosage. It is not difficult to make microbes resistant to penicillin in the laboratory by exposing them to concentrations not sufficient to kill them and the same thing has occasionally happened in the body. (Fleming, 1945)
The success of penicillin in treating infectious illnesses led to the discovery of more antimicrobial compounds. (Hudzicki, 2012) As more antibiotics were discovered, they were also indiscriminately prescribed to treat nearly every infection, even non-bacterial infections. (Alanis, 2005) In the 1940s, the widespread availability of penicillin and the subsequent discovery of streptomycin led to a dramatic reduction in illness and death from infectious diseases. However, bacteria have the ability to mutate and thereby develop resistance to antimicrobial drugs. (The Interagency Task Force on Antimicrobial Resistance, 2011) Fleming’s concern was soon realized with Staphylococcus aureus demonstrating resistance to penicillin within one year of widespread use of the drug. (Alanis, 2005).
Development of bacterial resistance to the antimicrobial drugs identified the need to determine a given bacterium’s susceptibility or resistance to a given drug. The original method of determining susceptibility to antimicrobials used time consuming broth dilution methods. This prompted the development of a simpler and quicker procedure to determine antibiotic resistance. In the mid-1950s, W. M. M. Kirby and his colleagues proposed a single disk method...