Chemotherapeutic agents are antimicrobial chemicals (natural or synthetic) that can be used internally or may be absorbed. The purpose of antimicrobial drugs is either to inhibit virus replication, without harming host tissues or to interrupt the cell processes or structures of bacteria, fungi, and protozoa. This lab has brought great interest to me because this is the way physicians’ control/treat infectious disease within our bodies. In this lab, chemotherapeutic agents were evaluated by the disk- diffusion method.
Chemotherapeutic agents are placed on the surface of a Petri plate containing Mueller-Hint agar, which allows the agents to diffuse freely, and a growth medium is incubated over its’ surface. During incubation, the chemotherapeutic agents move from levels of high concentration, to low levels of concentration. To be effective, the agent must inhibit bacteria growth and measurements that were made by the zones of inhibition around the Petri disk.
Zone size is affected by diffusion rate of the antibiotic and growth rate of the organism. The Minimum Inhibitory Concentration (MIMIC) is represented by the incineration of chemotherapeutic that stands at the edge of the zone of inhibition. The MIMIC is determined by comparing the zone of inhibition with the *Table 1 MIMIC values. The cultures assigned were Staphylococcus erasures (gram positive bacteria), and Escherichia coli (gram negative bacteria). However, results that are shown are from Escherichia coli.
Antimicrobial Lab Report
The antibiotics used were Backtracking, Penicillin, Streptomycin, and Tetracycline. The antibacterial reaction as a whole relies upon the relationship between the cell wall and the antibiotic. The effectiveness of one antibiotic to another can be tested through a reoccurred called the Kirby-Bauer test. The test is administered to measure the degree of bacterial susceptibility to antibiotics using tablets of chemotherapeutic drugs and Mueller-Hint agar plates, which allows the antimicrobial agent to diffuse freely. *Table 1. : Interpretation of Inhibition Zones of Test Cultures- look on lab manual page 143 Materials and Methods: First Period materials: -Petri plate containing Mueller-Hint agar – Sterile cotton swabs – Dispenser and antimicrobial disks (Backtracking, Penicillin, Streptomycin, and Tetracycline) – Forceps – Alcohol Second Period materials: Ruler *The only culture used was the Escherichia coli broth Techniques required: – Inoculating loop technique Aseptic technique The procedure for this experiment was fairly simple. First make sure that proper sanitation and protection of the work area and experimenters have been done.
Then proceed to taking the aseptically swab to the assigned culture onto the appropriate plate. Swab in three different directions (Starting at the top of the agar, swab back and forth across the plate. Then rotate it to a 45-degree angle and streaked again and once more afterwards) to make sure that the plate has en completely covered. Let the assigned culture sit for 5 minutes then proceed to placing the antimicrobial disks onto the agar. Make sure to sterilize the loop between each disk placement. To do this, dip into alcohol and then hold it over the Bunsen burner flame for at least ten seconds.
To secure its place onto the agar, tap the disk lightly into the agar. The inverted plate is then incubated at 35 degrees Celsius for 48 hours. This was done three more times with the remaining broth cultures. The results are measured in diameters of the zones in millimeters. Record the zone size and using Table 1, indicate whether the organism is Susceptible, intermediate, or resistant. Results: Antimicrobial Agent Disk Code Escherichia coli Zone Size / S, l, or R Penicillin P-100 IR Backtracking B-100 IR Streptomycin S-OHIO / R Tetracycline T-II 18/ Blank –0 / R Table 2. : Results of Kirby-Bauer test R = resistant; I = intermediate; S = Susceptible Results for Escherichia coli: Penicillin (P-10) was measured at Mom in diameters. There was no susceptibility. Therefore, with the zone size as O, Escherichia coli was resistant to penicillin. Tetracycline (T-10) was only one measured at mm in diameter. This zone size falls in the category of Escherichia coli having an intermediate resistance (Table 1) to the antimicrobial agent. **The only one that had any effect!
Backtracking (B-1 0) was measured at Mom in diameters. There was no susceptibility. Therefore, with the zone size as O, Escherichia coli was resistant to backtracking Streptomycin (S-II) was measured at Mom in diameters. There was no susceptibility. Therefore, with the zone size as 0, Escherichia coli was resistant to streptomycin. Discussion: In this experiment we were able to conclude that Tetracycline was the only antimicrobial agent that the Escherichia coli was resistant to; it was only one measured at mm in diameter.
Tetracycline is used to treat bacterial infections, including pneumonia and other respiratory tract infections; acne; infections of skin, genital and urinary systems; and the infection that causes stomach ulcers (Helicopter pylori). It also may be used as an alternative to other medications for the treatment of Lime disease and for the treatment and prevention of anthrax (after inhalation exposure). Tetracycline is in a class of medications called tetracycline antibiotics. It works by preventing the growth and spread of bacteria.
Referring back to the results, I was lucky to still have been able to read my results within the error that I made. When I was sterilizing the loop, I accidental let a couple drops of ethanol fall onto my tetracycline disk. Another error was that the disk was pushed too far into the agar. Within these mistakes however, my results were still accurate in comparison to the class’ results. The experiment overall was easy to do, the only thing think could have been done ore accurately was the measurement of the zone size.