Penicillin Susceptibility Testing of Staphylococcus aureus in the Clinical Lab: Work in Progress

CLSI and EUCAST disk-based testing methods for penicillin susceptibility have high error rates.

The increase in penicillin-susceptible Staphylococcus aureus (PSSA) has muddied susceptibility testing and optimal therapy; despite penicillin's pharmacokinetic advantages for treating PSSA infections, susceptibility testing is not performed in many clinical laboratories because of concern about inaccuracies of beta-lactamase detection methods. Absence of blaZ penicillinase gene detection by PCR is considered the gold standard for PSSA identification.

Henderson et al. studied 9 PSSA isolates, 6 of which harbored blaZ. Five of these strains had disk diffusion zones smaller than the susceptible breakpoint. The sixth strain had a susceptible-sized zone, but the sharpness of the zone's edge, rather than its size, was deemed the basis of phenotyp…

Reviewing Author

George Sakoulas, MD

Disclosures

Consultant/Advisory BoardParatek Pharmaceuticals; Nestle Corp.; AbbVie; Shionogi

Speaker’s BureauAllergan/AbbVie; Paratek Pharmaceuticals; Nestle Corp.

RoyaltiesUpToDate

Editorial BoardsAntimicrobial Agents and Chemotherapy; Open Forum Infectious Diseases