Activity of Minocycline Against Multidrug-Resistant Isolates-Evaluation of Clinical Breakpoints and Review of Literature.

Therapeutic options for the treatment of infections by multidrug-resistant strains are often limited. Minocycline (MIN) is an old antibiotic, with excellent activity against isolates, which can be administered orally. Currently, there is no single criterion regarding the breakpoints for MIN and The activity of MIN was examined against a collection of isolates recovered from 15 hospitals of 6 countries of South America. A review of the literature was also performed. In our series and most of the studies, the percentages of MIN susceptible isolates exceeded 50%, regardless of the breakpoints utilized (4-2 or 1 μg/mL). However, a greater number of isolates not harboring Tet B were considered resistant with the breakpoints of 1 or 2 μg/mL, whereas isolates with (B) genes were still detected with minimum inhibitory concentration below all breakpoints considered. Tetracycline susceptibility may be used as a screening to discriminate the populations with and without acquired resistance mechanisms to MIN. In this study, MIN-resistant subpopulations were found in isolates harboring Tet B, with MIC ≤1 μg/mL, and their frequency increased after incubation with MIN. These subpopulations were not detected in isolates not harboring Tet B. The clinical correlation of these subpopulations should be evaluated in future studies.