Comparative in vitro activity of plazomicin and older aminoglyosides against Enterobacterales isolates; prevalence of aminoglycoside modifying enzymes and 16S rRNA methyltransferases.

Comparative in vitro activity of plazomicin and 4 older aminoglycosides was evaluated with broth microdilution in 714 blood isolates from 14 hospitals in Turkey. Isolates included Escherichia coli (n=320), Klebsiella spp. (n=294), Enterobacter spp. (n=69), Serratia marcescens (n=20), and Citrobacter spp. (n=11). Isolates resistant to older aminoglycosides (n=240) were screened for aminoglycoside modifying enzyme genes: aac(6')-Ib, aac(3)-Ia, aac(3)-IIa, ant(2″)-Ia. Isolates with high MICs for plazomicin (n=41) were screened for 16S rRNA methyltransferase genes (armA, rmtA, rmtB, rmtC, rmtD, rmtE, rmtF, rmtG, rmtH, npmA) and 2 carbapenemase genes (blaOXA-48, blaNDM-1). Overall, resistance to plazomicin, amikacin, netilmicin, gentamicin, and tobramycin was 7.7%, 7.4%, 31.5%, 32.9%, and 34.7%, respectively. aac(6')-Ib and aac(3)-IIa were the most common AME genes. Co-occurrence of blaNDM-1 with armA and rmtC and blaOXA-48 with armA was striking. Enterobacter cloacae carrying rmtC+blaNDM-1, S. marcescens with armA+blaOXA-48, and rmtF+ blaOXA-48 in K. pneumoniae were reported for the first time.