How Do Microbiologists Use Antimicrobial Susceptibility Testing?

In order to determine which ones would be resistant, intermediate, and susceptible to our unknown strain of E. coli we had three antibiotics and one control per agar plate, and we replicated this twice. A lawn of the E. coli strand was spread evenly on each agar plate with a cotton swab. We then divided the agar plate into four halves and placed an antibiotic sample in each half with forceps. We incubated the dishes for forty-eight hours. Our independent variables are the different types of antibiotics with our known and unknown E. coli that we used to conduct the experiment and our dependent variables are the diameters of the zone of inhibition for each antibiotic.

Gold standard procedures should be implemented with the aim of providing timely and accurate results. (Schentag) The culture result should be accompanied by its clinical significance, selective reporting of susceptibility testing results in accordance with hospital antimicrobial therapy guidelines and suggested management. (Schentag) This encourages appropriate prescribing and minimises unnecessary use of antimicrobials. The clinical microbiology team should also provide reports to AMS regarding resistant organisms.

Modern-day advances have allowed scientists to develop methods to control pathogens. The more common methods include the use of antiseptics, antibiotics, and vaccines. By definition, antiseptics are chemicals used to kill pathogens. A few widespread antiseptics include soap, vinegar, and rubbing alcohol. Antiseptics are primarily used for the external destruction of pathogens, while antibiotics and vaccines target internal pathogens. Nevertheless, there are and can be difficulties concerning the use of antibiotics. “As antibiotic use has become more common, antibiotic-resistant bacteria have evolved.” This resistance due to evolution is called antibiotic resistance. It results in the antibiotics having no effect whatsoever on the bacteria, rendering the antibiotics useless. When antibiotic resistance occurs, scientists must resume their search to create a new medicine to can kill the mutant bacteria.

AIM – The aim of the experiment is to determine the relative effectiveness of several anti-microbial substances on developing pathogens. (E. coli)

This is important in the medical field because identification of unknown bacteria can help treat a patient by knowing the contributing source of a disease. Also knowledge of different bacteria helped others make antibiotics used today. This lab was completed by using the methods learned thus far in identification of bacteria.

The antibiotics will have different zones of inhibition on different bacteria. Also, a range of concentrations of the nutrients in the bacteria will change the bacterial growth.

The aim of this investigation was to find out which antiseptics were most effective at preventing the growth of bacteria.

E.coli outbreaks have steadily grown over the last few decades. An expansion in big farming has led to E. coli not only being found in meat, but vegetation as well, due to waste runoff. This has increased our need for adequate antibiotics that can fight bacteria, like E. coli. The best way to pinpoint which antibiotics work is by measuring their ability to create antimicrobial agents or zones of inhibition. When a paper disc that has been saturated in an antibiotic is inserted in a solution of E.coli and medium, the zone of inhibition will be noted as the clear ring that forms around the disk. The antibiotics efficacy is then determined by measuring each disk zone of inhibition, and comparing these measurements to the zone measurements of an untreated specimen. If an antibiotic is to be deemed sufficient for treating E. coli it should show a zone of inhibition that is at least double the size of the untreated specimen.

Penicillin (P-10) was measured at 0mm in diameters. There was no susceptibility. Therefore, with the zone size as 0, Escherichia coli was resistant to penicillin.

The Kirby- Bauer method is used to test antibiotics sensitivity to the microbe. Some antibiotics have broad-spectrum effect, which means they inhibit the growth of more than one microbe; while narrow spectrum only have an effective on one group of microbe. In order for this test to be effective a lawn of bacteria has to be made on Mueller- Hinton agar. This agar does two amazing things in the world of science. It contains a starch that makes it test plate transparent (easy to read results) and it control the rate of diffusion of the tested drug. Ampicillin, Gentamicin, Gentamicin, penicillin, and vancomycin are the fours types of antibiotics that were use to test the sensitivity of the microbe to them. The microbe was resistant to Ampicillin;

After 48 hours, the experimenter was able to obtain the Petri dish in order to observe what had taken place, within the nutrient agar plate, of the span of this period of time. The experimenter was able to establish that any clear areas surrounding the filter-paper disks were the zones of inhibition and they indicated that the antibiotic was able to inhibit the bacterial growth, and any cloudy areas of the agar demonstrated that bacterial growth was still able to take place within the given conditions. Thus, the larger the zone of inhibition, the more bacteria was inhibited within this specific environment. Quadrant 1 contained an Erythromycin filter-paper disk, which was able to inhibit the growth of Bacteria D. The Erythromycin filter-paper

The purpose of this study and experiment was to analyze and compare the relative antibiotic resistance of the gram-negative bacterial species Serratia marcescens to the antimicrobial species streptomycin and ampicillin. Preceding researches have shown that streptomycin has a stronger effect on the bacteria species than the ampicillin. In this experiment, the disc-diffusion method has been introduced and the zone of inhibition was measure in millimeters around the disc saturated with the same molar concentration of the two antibiotics- streptomycin and ampicillin. The hypothesis is that if the colonies of S. marcescens were treated separately with streptomycin and ampicillin with all other factors remaining the same and controlled, the S. marcescens would display a stronger resistance toward the ampicillin than to streptomycin. The results from the experiment supports the hypothesis that S. marcescens is more resistant to ampicillin than to streptomycin.

The Kirby-Bauer disc diffusion method was used to examine sensitivity of antimicrobial agents, it fast and simple way to find an antibiotic to use for a treatment of some type of infection. This method uses a plate that has been cover with the testing bacteria and small disc covered in the antibiotic to see if the bacteria is able to around the disc, it will make an even circle around the disc which is the zone of inhibition. This zone of inhibition diameter can be measured and compared to the interpretation chart to find the antibiotic sensitivity or resistance. When the zone of inhibition is very small or nonexistent this shows that bacteria is resistant to the antibiotic and will not work against this bacterial infection. If the zone is

Antibiotic resistance is a highly selectable phenotype and can be detected using growth inhibition assays performed in broth or by agar disc diffusion. In a dilution-based growth inhibition assay, the minimum inhibitory concentration (MIC) of an antibiotic can be calculated for each bacterial isolate and the organism is typically interpreted as being susceptible or resistant to the antibiotic [Schmieder, R]. Of course, there is a gradation of resistance and some classification schemes include one or more intermediate levels. For clinically important bacteria, diagnostic laboratories perform phenotypic-based analyses using standardized susceptibility testing methods, usually in accordance Research targeted towards antibiotics for treating infectious diseases and the risks to human health posed by antibiotic resistance have focused mainly on the clinical setting. To fully understand the development and dissemination of resistance, we need to address the study of

The main objective of this experiment is to investigate the effect of different types of antibiotics on bacteria Bacillus subtilis and Escherichia coli. Some of the main methods used in this experiment