Question

multiple choice question
using the table below, determine which antibiotic would be a poor choice to treat an infection caused by staphylococcus aureus.
table with columns: drug, zone size (mm) required for susceptibility, zone size (mm) required for resistance, example results (mm) for staphylococcus aureus. rows:
bacitracin: >13, <8, 15
chloramphenicol: >18, <12, 20
erythromycin: >18, <13, 15
gentamycin: >13, <12, 16
kanamycin: >18, <13, 20
neomycin: >17, <12, 12
penicillin g: >29, <20, 10
polymyxin b: >12, <8, 10
streptomycin: >15, <11, 11
vancomycin: >12, <9, 15
tetracycline: >19, <14, 25

Explanation:

Step1: Analyze Penicillin G

For Penicillin G, the required zone size for susceptibility is \(>29\) mm, and the example result is \(10\) mm. Since \(10 < 29\), it is resistant.

Step2: Check Other Drugs (e.g., Bacitracin)

For Bacitracin, required susceptibility zone \(>13\) mm, result \(15\) mm (\(15>13\)) – susceptible. Chloramphenicol: required \(>18\), result \(20\) (\(20>18\)) – susceptible. Erythromycin: required \(>18\), result \(15\) (\(15<18\))? Wait, no, re - check. Wait, Penicillin G: resistance zone is \(<20\), result \(10<20\) (resistant), and susceptibility zone \(>29\), \(10<29\). So Penicillin G has a zone size (10 mm) that is less than the susceptibility requirement (>29 mm) and meets the resistance requirement (<20 mm), making it a poor choice.

Answer:

Penicillin G (since its example result of 10 mm is less than the susceptibility requirement (>29 mm) and meets the resistance requirement (<20 mm), indicating resistance and thus a poor choice for treating Staphylococcus aureus infection)