Retention of Minocycline Susceptibility When Gram-Positive Periprosthetic Joint Infection Isolates Are Non-Susceptible to Doxycycline

Background: The treatment of hardware infections often utilizes chronic oral suppression antibiotics to prevent infection recurrence. However, when methicillin-resistant Staphylococcus aureus and other bacteria are non-susceptible to doxycycline, limited oral antibiotic options can be available that do not cause significant side effects and drug–drug interactions. Consequently, the purpose of this study was to evaluate the ability of Gram-positive clinical prosthetic joint infection isolates that were non-susceptible to doxycycline and to retain susceptibility to minocycline. Methods: Twenty-six Gram-positive prosthetic joint infection isolates that were not susceptible to doxycycline were evaluated for retained minocycline susceptibility with the use of minocycline gradient diffusion test strips. Results: All five of the coagulase-negative staphylococcal isolates and eight of the eleven methicillin-resistant S. aureus isolates were susceptible to minocycline, despite being doxycycline non-susceptible. None of the five Enterococcus faecium PJI isolates retained susceptibility to minocycline and only two of the five E. faecalis isolates (n = 5) were susceptible to minocycline. Conclusions: The findings have direct clinical implications supporting minocycline susceptibility testing for patients with PJI and other hardware-associated infections, which have isolates that are doxycycline non-susceptible to thereby provide alternative suppression antibiotic options.