Question

Antibiotic	Spectrum	Mechanism of Action
Penicillin	Broad	Inhibits functioning of transpeptidase
Oxacillin	Narrow (Gram +)	Inhibits functioning of transpeptidase
Amoxicillin – clavulanic acid	Broad	Amoxicillin inhibits peptidoglycan formation; clavulanic acid inhibits beta-lactamases that destroy amoxicillin
Cefazolin	Broad	Inhibits peptidoglycan formation
Vancomycin	Narrow (Gram +)	Inhibits synthesis of peptidoglycan
Gentamicin	Narrow (Gram -)	Inhibits protein synthesis
Tetracyclins	Broad	Inhibits protein synthesis
Trimethoprim-sulfa-methoxazole	Broad	Inhibits synthesis of folic acid which is needed for bacteria to survive
Polymyxin B	Narrow (Gram -)	Disrupts cell membrane structure and therefore permeability
Streptomyocin	Broad	Inhibits protein synthesis

Objective of experiment : Determine which antibiotics/antibacterails that you test are effective at preventing growth B. subtilis (Gram +) and E. coli (Gram -) growth.

a. In a short paragraph, explain why the plates you set up with specific bacteria and disk combinations will best help you to answer the Experiment Objective.

b. In a short paragraph, describe your predicted results. For your antibiotics, use the table of common antibiotics and their properties (Table) to help you make your predictions. For your antibacterials, you can make more generalized predictions since you do not have a table of common antibacterials and their properties.

Answer 1

A) The objective of the experiment was to determine which antibiotics are effective at preventing growth of B. subtilis and E. coli. For this, different plates are setup with specific bacteria and antibiotic to test for the antibiotic sensitivity. This is known as antibiotic sensitive assay. The sensitive antibiotics are identified by greater zone of inhibition around the disc.

B) The broad prediction about antibiotics are that the penicillins and cephalosporins have a broad spectrum of action against both gram positive and negative bacteria. Vancomycin and oxacillin are effective only against gram positive while gentamicin and polymyxin B are effective only against gram negative bacteria.