Abstract

The emergence of 16S rRNA methyltransferase (16S-RMTases) poses a major therapeutic challenge, as they confer high-level resistance to all clinically relevant aminoglycosides. In Chile, data on these enzymes remain scarce. This study investigated the epidemiological distribution and genetic relatedness of Klebsiella pneumoniae strains carrying 16S-RMTase genes. Antibiotic susceptibility was assessed using the Kirby-Bauer method and complementary techniques. Gene detection was performed via conventional PCR, and genotyping via ERIC-PCR. Among 1,200 K. pneumoniae clinical strains collected between 1997 and 2023; 233 (19.4%) exhibited high-level resistance to both amikacin and gentamicin, suggesting 16S-RMTase gene carriage. All presumptive strains carried 16S-RMTase genes, with rmtG being the most prevalent (n = 174), followed by armA (n = 30), rmtC (n = 24), and rmtD (n = 5). Genotyping revealed 19 distinct clusters. The rmtG gene was widely distributed, whereas rmtC displayed regional clustering, particularly in Concepci & oacute;n, and was associated with broader resistance profiles, including resistance to carbapenems. In contrast, rmtG-positive strains retained partial susceptibility to these agents. Fisher's exact test revealed associations (p < 0.05) between specific 16S-RMTase genes and non-susceptibility antibiotic profiles. The spread of 16S-RMTase genes since 2007, from Iquique to Puerto Montt, highlights their growing clinical relevance. The recent rise of armA and rmtC suggests a shift in dominant resistance mechanisms.