Characterization of conjugative plasmids mediating the disemination of 16S ribosomal RNA methylases responsible for panaminoglycoside resistance of clinical Enterobacteriaceae in a Bulgarian cancer hospital

During 2004-2005, high-level resistance to aminoglycosides due to 16S ribosomal RNA methylation was identified in 20 strains of the family Enterobacteriaceae, including Klebsiella pneumoniae, Escherichia coli, Citrobacter freundii, Enterobacter cloacae, Serratia marcescens and Klebsiella oxytoca, at the cancer center of Sofia. The ArmA methylase-mediated aminoglycoside resistance was transferable by conjugation and carried by IncLM plasmids ranging in size from ca. 80.6 to 99.3 kilobase pairs. In addition, all ArmA plasmids carried the following genes: bla_CTX-M-3 (extendedspectrum beta-lactam resistance), bla_TEM-1 (ampicillin resistance), ant3"9 (streptomycin-spectinomycin resistance), aac3-II (gentamicin-tobramycin-netilmicin-kanamycin resistance), dfrXII (trimethoprim resistance), sul1 (sulfonamide resistance) and intI1, an integrase associated with class 1 integrons. We conclude that ArmA-mediated panaminoglycoside resistance was disseminated across various species in the family Enterobacteriaceae by closely related, broad-host-range IncLM conjugative plasmids, which conferred similar multidrug resistance phenotypes.