Prevalence and Molecular Characteristics of 16S rRNA Methylase Genes in Clinical Isolates of Carbapenem-Resistant Enterobacterales.

Objective: To analyze the prevalence and molecular characteristics of 16S rRNA methylase genes in clinical isolates of carbapenem-resistant Enterobacterales, for clinical doctors provide a reference basis for the rational use of drugs.

Methods: The Enterobacterales isolated from our hospital from 2020 to 2022 were selected and identified by VITEK 2 Compact automatic bacterial identification instrument. Resistance genes were detected by polymerase chain reaction.

Results: A total of 180 carbapenem-resistant Enterobacterales were isolated, of which 158 (87.8%) were resistant to at least one aminoglycoside. The resistance rates to gentamicin, tobramycin and amikacin were 85.0%,82.8% and 54.4%, respectively. Compared with 16S rRNA methyltransferase negative isolates, the positive isolates were more sensitive to trimethoprim-sulfamethoxazole, tetracycline and minocycline, but had higher resistance rates to aztreonam, tobramycin, gentamicin, amikacin and ciprofloxacin. The resistance rates of 16S rRNA methyltransferase gene positive strains to most commonly used antibiotics were more than 80%. But the rates for colistin and tigecycline were less than 10%. There were 114 strains (63.3%) positive for 16S rRNA methyltransferase genes, mainly rmtB, accounting for 70.2%. The positive rates of other armA, rmtA and armA+rmtB genes were 22.8%, 4.4% and 2.6%, respectively. No rmtC, rmtD, rmtE and npmA genes were detected. In addition, 175 of the 180 carbapenem-resistant Enterobacterales carried at least one carbapenemase genes. The bla_KPC was the main one (115, 65.7%). There were 111 (61.7%) strains carried both carbapenemase and 16S rRNA methyltransferase genes, simultaneously. Compared with 16S rRNA methyltransferase negative strains, the positive strains carried more bla_KPC genes and less bla_NDM genes, with P values of 0.034 and 0.003, respectively.

Conclusion: bla_KPC and rmtB genes are the main resistance mechanisms of Enterobacterales to carbapenems and aminoglycosides in our hospital. It is necessary to strengthen the detection of multi-drug resistant strains to provide scientific basis for clinical rational drug use.