Nosocomial spread of armA-mediated high-level aminoglycoside resistance in Enterobacteriaceae isolates producing CTX-M-3 beta-lactamase in a cancer hospital in Bulgaria.

1,310 Enterobacteriaceae, 242 Pseudomonas aeruginosa and 97 Acinetobacter baumannii clinical isolates collected at a cancer hospital in Bulgaria were screened for the presence of 16S rRNA methylases. The armA methylase gene was identified in 20 (1.5%) Enterobacteriaceae (7 Klebsiella pneumoniae, 3 Escherichia coli, 3 Serratia marcescens, 3 Citrobacter freundii , 3 Enterobacter cloacae and 1 Klebsiella oxytoca). ArmA-mediated aminoglycoside resistance was transferable by conjugation and carried by closely related IncL/M plasmids which also carried ant3"9, dfrXII, sul1, bla(TEM-1), and bla(CTX-M-3) genes encoding resistance to streptomycin-spectinomycin, trimethoprim, sulfonamides, and ss-lactams, respectively. Most of the isolates were genetically different according to PFGE but shared similar restriction patterns of the armA -encoding plasmids. Our findings highlight the strong association of armA and bla(CTX-M-3) extended-spectrum ss-lactamase genes across various species in the family Enterobacteriaceae . The spread of multiresistant isolates expressing 16S rRNA methylases and ESBLs is a worrisome development requiring continuous monitoring.