Antimicrobial susceptibility and genetic mechanisms of resistance of <i>Ureaplasma</i> isolates in North America between 2012 and 2023

We analyzed antimicrobial susceptibilities of 415 <i>Ureaplasma</i> isolates from various sample types derived from different regions of the United States and Canada from 2012 to 2023 and investigated the genetic mechanisms of antimicrobial resistance. Minimum inhibitory concentration (MIC) ranges for erythromycin, tetracycline, and levofloxacin were 0.063-256, 0.016-64, and 0.063-32 µg/mL, respectively. MIC₅₀ values for erythromycin, tetracycline, and levofloxacin were 2, 0.25, and 1 µg/mL, and MIC₉₀ values were 4, 1, and 2 µg/mL, respectively. According to Clinical and Laboratory Standards Institute breakpoints, there were 61 (14.7%) isolates resistant to one or more drugs, and resistance rates for erythromycin, tetracycline, and levofloxacin were 2.4% (10/415), 6.5% (27/413), and 6.7% (28/415), respectively. Four isolates (1.0%) were resistant to two drugs. Mutations in domain V of 23S rRNA, mainly A2058G (<i>Escherichia coli</i> numbering), and/or in the <i>rpl</i>D gene encoding ribosomal protein L4 were identified in most erythromycin-resistant isolates. <i>Tet</i>(M) was detected in all isolates with tetracycline MIC ≥4 µg/mL but absent in 64.7% (11/17) of isolates with MIC of 2 µg/mL. For fluoroquinolone-resistant isolates, C248T (S83L) and G259A (E87K) mutations in <i>parC</i> were identified in most cases (23/26). In summary, erythromycin, tetracycline, and levofloxacin are still effective <i>in vitro</i> against most <i>Ureaplasma</i> isolates in North America.