Rank the following antibiotics for Staphylococcus epidermidis infection from most to least effective according to the described results: novobiocin, gentamicin, penicillin.

Rank the following antibiotics for Staphylococcus epidermidis infection from most to least effective according to the described results: novobiocin, gentamicin, penicillin.

• A. Novobiocin, then Gentamicin, then Penicillin
• B. Gentamicin, then Novobiocin, then Penicillin
• C. Penicillin, then Gentamicin, then Novobiocin
• D. Gentamicin, then Penicillin, then Novobiocin

Answer: (A)

Novobiocin is most effective against Staphylococcus epidermidis in this set because this species is typically susceptible to novobiocin, a trait often highlighted in labs to distinguish S. epidermidis from novobiocin-resistant S. saprophyticus. Gentamicin provides some activity against staphylococci, but its effectiveness can be variable due to resistance mechanisms and uptake limitations, so it doesn’t reach the same level of reliability as novobiocin in this context. Penicillin, on the other hand, is usually least effective because many S. epidermidis strains produce beta-lactamase, which inactivates penicillin. Put together, the results rank novobiocin highest, then gentamicin, then penicillin.

Novobiocin is most effective against Staphylococcus epidermidis in this set because this species is typically susceptible to novobiocin, a trait often highlighted in labs to distinguish S. epidermidis from novobiocin-resistant S. saprophyticus. Gentamicin provides some activity against staphylococci, but its effectiveness can be variable due to resistance mechanisms and uptake limitations, so it doesn’t reach the same level of reliability as novobiocin in this context. Penicillin, on the other hand, is usually least effective because many S. epidermidis strains produce beta-lactamase, which inactivates penicillin. Put together, the results rank novobiocin highest, then gentamicin, then penicillin.