Omadacycline In Vitro Activity Against a Molecularly Characterized Collection of Clinical Isolates with Known Tetracycline Resistance Mechanisms

This study evaluated the in vitro activity of omadacycline against a broad collection of clinical isolates with molecularly characterized tetracycline resistance mechanisms. A total of 167 Gram-positive and Gram-negative clinical isolates from the worldwide SENTRY Antimicrobial Surveillance Program, the vast majority (79%) from the 2016 sampling year, were included in this study.

Against tetracycline-resistant Gram-positive isolates, omadacycline (MIC50/90, 0.12/0.25 µg/mL) and tigecycline (MIC50/90, 0.06/0.25 µg/mL) showed similar results tested against Staphylococcus aureus carrying tet(K). Omadacycline (MIC90, 0.25-2 µg/mL) and tigecycline (MIC90, 0.12-1 µg/mL) showed potent MIC results against Gram-positive isolates carrying tet(L) and/or tet(M). Tetracycline and doxycycline had MIC90 values of ≥8 µg/mL against isolates carrying tet genes, except for doxycycline (MIC50/90, 0.5/0.5 µg/mL) that was active against those carrying tet(K) genes. Against tetracycline-resistant Gram-negative isolates, omadacycline (MIC50/90, 1/4 µg/mL) and tigecycline (MIC50/90, 0.25/0.5 µg/mL) had the lowest MIC results against Gram-negative Enterobacteriaceae isolates carrying tet(B). Omadacycline showed MIC50 results of 2, 4, and 4 µg/mL, respectively, against isolates carrying tet(D), tet(A), and tet(A)+tet(D). Among tetracyclines, omadacycline (MIC50/90, 2/8 µg/mL) and tigecycline (MIC50/90, 0.5/2 µg/mL) demonstrated the lowest MIC results when tested against Gram-negative isolates harboring a combination of other tet genes. Tetracycline and doxycycline were not active (62.5-100.0% resistance) in vitro against Gram-negative Enterobacteriaceae isolates carrying tet genes. These results indicate that omadacycline is not adversely affected against molecularly characterized Gram-positive clinical isolates carrying commonly acquired tet genes.

Source: Mendes RE, et al. IDWeek 2018. Abstract 1377.

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