Plasmid-borne 16S rRNA methylase ArmA in aminoglycoside-resistant Klebsiella pneumoniae in Poland.

We characterized 17 clinical isolates of Klebsiella pneumoniae producing 16S rRNA methylase ArmA. The isolates originated in Poland from 2002 to May 2010 and encompassed four XbaI-PFGE clusters. All the isolates were resistant to amikacin, gentamicin and kanamycin (MIC range: 256-1024 mg l(-1)) and carried the armA gene on a large plasmid of approximately 90 or 130 kb in 15 and 2 isolates, respectively. The armA gene was found in a ~10 kb ClaI restriction fragment of the large plasmid and was flanked by the same elements as in Tn1548. All the isolates carried the bla(CTX-M) gene for a CTX-M-type extended-spectrum β-lactamase. Our results show that ArmA has disseminated horizontally among K. pneumoniae isolates in Poland on the ~90 kb plasmid of the pCTX-M3 family.