Trends in the susceptibility of US Acinetobacter baumannii-calcoaceticus species complex and Stenotrophomonas maltophilia isolates to minocycline, 2014-2021

Acinetobacter baumannii-calcoaceticus species complex (ACB) and Stenotrophomonas maltophilia (SM) are opportunistic, non-fermentative organisms that can cause serious hospital-acquired infections in immunocompromised patients. These pathogens are inherently resistant to several common drug classes and often acquire other resistance mechanisms, making them difficult to treat. In this study, we analyzed the susceptibility of 1,029 contemporary ACB and 1,522 SM isolates to minocycline (MIN) and levofloxacin (LEV) as well as meropenem (MER) for ACB and trimethoprim-sulfamethoxazole (TMP/SMX) for SM using the CLSI broth microdilution method. Isolates were collected as a part of the SENTRY Antimicrobial Surveillance Program from 2014 to 2021. Pneumonia in hospitalized patients was the most common infection from which ACB (57.0%) and SM (73.9%) were isolated. MIN had the highest in vitro activity for ACB (86.2%) and SM (99.5%). The activity of ACB and SM to all three agents varied over the period studied. MIN activity to ACB decreased in 2020 (80.6%) but rebounded in 2021 (86.2%). LEV and MER showed an overall trend of increasing susceptibility for ACB, with slightly lower activity in 2020-2021. MIN and TMP/SMX (>98.3% and >93.7%, respectively) activities were stable against SM isolates. LEV activity decreased from 84.3% (2015) to 69.2% (2018). The activity of MIN remained stable and higher than other agents tested for both ACB and SM, pathogens that have limited therapeutic alternatives. These in vitro data suggest that MIN is a useful treatment option for infections caused by ACB or SM.