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Antibiotics lab report
General Microbiology (BIO SCI-356)
University of Wisconsin-Milwaukee
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Barbara Yurkiewicz
Bio Sci 383-
March 2, 202
Antibiotics, Antiseptics, and Disinfectants
I. Purpose The main purpose of this lab is to test and compare the effectiveness of antibiotics, antiseptics, and disinfectants against Gram-positive and Gram-negative bacteria. II. Procedure I did not personally perform this experiment. I am in an online lab section, so the procedure was conducted by the lab TA for lab section 908. From the recorded and uploaded videos of the procedure, as it was being performed, the two plate swabs of both E. coli and S. aureus cultures were performed according to the procedure outlined on page 32 in the lab supplement. The application of the antibiotics (steps 1-4 under antibiotics, page 32), antiseptics, and disinfectants (steps 1-4under antiseptics and disinfectants, pages 32-33) were also performed according to the procedure, via the Kirby-Bauer disc diffusion method. The plates were then incubated at 30o C for 48 hours. The antibiotics used were penicillin, erythromycin, tetracycline, and chloramphenicol. The antiseptics used in this experiment were Listerine and hand soap, while the disinfectants used were Pine-sol and yellow Lysol. The results used for the data, calculations, and lab questions were from results set 4.
III. Results and Calculations
Tetracycline Antibiotic Zone of Inhibition (mm) 23 Sensitivity/Resistance Sensitive ChloramphenicolErythromycin 2224 SensitiveSensitive Antiseptic/Disinfectant Penicillin Zone of Inhibition (mm) 37 Sensitive Hand soapListerine 140 Lysol yellowPine-sol 146 Table 1. Data obtained from cultured plates of S. aureus. All plaques appeared as clear zones with no visible bacterial growth Tetracycline Antibiotic Zone of Inhibition (mm) 23* Sensitivity/Resistance Sensitive* ChloramphenicolErythromycin 2716 IntermediateSensitive Antiseptic/Disinfectant Penicillin Zone of Inhibition (mm) 16* Intermediate* Hand soapListerine 140 Lysol yellowPine-sol 148 Table 2. growth still present. Therefore, sensitivity/resistaData obtained from cultured plates of E. coli nce interpretation, as indicated by the chart in the. * Zone of inhibition was not clear and direct, bu lab supplement, may not t cloudy with some accurately describe the effects of the antibiotic.
IV. Discussion Although the antibiotics proved useful against both S. aureus and E. coli , they were far more effective in inhibiting growth in S. aureus than in E. coli. This is due to E. coli being a Gram-negative bacteria and S. aureus being Gram-Positive. Gram-negative bacteria contain an additional outer cell wall that Gram-positive bacteria lack. This additional cell wall provides extra protection from those agents that interfere with the peptidoglycan layer. Thus, the plaques observed around the S. aureus growth were clear and contained little to no colonies, while the plaques surrounding E. coli growth were less distinct and appeared cloudy.
of amino acids to the peptidechains and blocking peptide Erythromycin Erythromycin Prevents protein synthesis bformation. 1 y bacterial cell membrane anddiffusion through the reversibly binding to the 50Ssubunit of the ribosome. 2 Lysol yellow Alkyl C12(67%), C14(25%),C16(7%), C8-C10-C18(1%), Dimethyl Benzyl AmmoniumChlorides(0%) membrane lipid bilayers ofDissociation of cellular compromised cellularbacteria, resulting in important cellular contents and leakage of Pine-sol Glycolic acid Disrupts bacterial cellwalls. Hand soap Triclosan thus disrupting bacterial fattyInhibition of ACP reductase, Listerine Menthol, Thymol, acid biosynthesis. 5 Eucalyptol, Methyl salicylate Involves bacterial cell wall inhibition, and extraction ofdestruction, enzymatic lipopolysaccharides. 1
V. Conclusion
Overall, I believe this experiment was successful. There are obvious differences in the zones of inhibition between the two bacteria. Since one is a Gram-positive species and the other a Gram-negative one, these differences in the effectiveness of the substances tested makes sense.
VI. Questions
- If any colonies were growing within the zone of inhibition, it would indicate resistance to the antibiotic, antiseptic, or disinfectant being tested. In the E. coli zones of inhibition, there were no single colonies present, but the zones were not as distinct as in the S.
aureus zones. This indicates that E. coli is more resistant to these substances than S. aureus. 2) Some factors other than antimicrobial activity that affect the size of inhibition zones include: The susceptibility of the pathogen, antibiotic diffusion effects, the depth of the agar, pH levels, the size of the organism, and the presence of contaminants. 3) No, not only does the effectiveness of the antibiotic depend upon whether bacteria are Gram-positive versus Gram-negative, but some antibiotics are narrow spectrum. This means that particular antibiotics are very specific in regards to which bacteria are going to be resilient of susceptible to them.
- pubmed.ncbi.lm.nih
- amrls.cvm.msu>antimicrobials
- scienceline.ucsb
- go.drugbank/lysol
- sciencedirect
- General Microbiology Laboratory supplement
Antibiotics lab report
Course: General Microbiology (BIO SCI-356)
University: University of Wisconsin-Milwaukee
