Annals of Clinical Microbiology, The official Journal of the Korean Society of Clinical Microbiology


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Molecular and Phenotypic Characteristics of 16S rRNA Methylase-producing Gram-negative Bacilli

Original article

Annals of Clinical Microbiology (Ann Clin Microbiol) 2010 March, Volume 13, Issue 1, pages 19-26.

Molecular and Phenotypic Characteristics of 16S rRNA Methylase-producing Gram-negative Bacilli

Hyukmin Lee1, Eun-Mi Koh2, Chang Ki Kim3, Jong Hwa Yum4, Kyungwon Lee5, Yunsop Chong5
1Department of Laboratory Medicine, Kwandong University College of Medicine, Goyang, 2 Incheon Blood Center, Korean Red Cross, Incheon, 3Korean Institute of Tuberculosis, Seoul, 4Department of Clinical Laboratory Science, Dongeui University, Busan, 5Department of Laboratory Medicine and Research Institute of Bacterial Resistance, Yonsei University College of Medicine, Seoul, Korea


Background: Blood culture is essential for diagnosis of sepsis. However, usually the available blood volume is not sufficient to meet the guidelines. Thus, periodic monitoring and feedback are essential to iBackground: Recently a novel plasmid-mediated resistant mechanism that conferred high-level resistance to aminoglycoside via methylation of 16S rRNA was reported. The aims of this study were to determine the prevalence of the 16S rRNA methylase genes and to characterize the coresistance to other antibiotics in Gram-negative bacilli. 

Methods: Consecutive non-duplicate Gram-negative bacilli were isolated from clinical specimens at a Korean secondary- and tertiary-care hospital from July 2006 to June 2007. The antimicrobial susceptibility was tested by the CLSI agar dilution method,and PCR was performed to detect the 16S rRNA methylase genes in the arbekacin-resistant isolates. 

Results: In Gram-negative bacilli, the proportions of 16S rRNA methylase gene-positive isolates were 5% (75/1,471) in the secondary-carehospital and 4% (48/1,251) in the tertiary-care hospital, and the positive rates by species were 1% Escherichiae coli 16% (10/1,062), Klebsiella pneumoniae 16% (75/ 460), K. oxytoca 2% (1/44), Citrobacter spp. 9% (7/ 82), Enterobacter spp. 2% (4/181), Serratia marcescens 6% (6/100), Proteus miriabilis 4% (2/57), Achromobacter xylosoxidans 20% (1/5), Pseudomonas aeruginosa <1% (1/505), Acinetobacter spp. 10% (11/ 112), and Stenotrophomonas maltophilia 2% (1/66), respectively. Among 16S rRNA methylase-positive isolates from secondary- and tertiary-care hospitals,93% (70/75) and 90% (43/48), respectively, were armA positive, and others, except one rmtA positive isolate, were positive for the rmtB gene, according to PCR results. The rates of ESBL-positive and cefoxitin-resistant K. pneumoniae were 59% and 92%, respectively. In addition, 91% of 16S rRNA methylase-producing K. pneumoniae were positive for qnrB. There were no MBL producers among 16S rRNA methylase-producing Pseudomonas and Acinetobacter species. 

Conclusion: The novel aminoglycoside-resistant mechanisms involving16S rRNA methylase were prevalent and widely distributed among Gram-negative bacilli in Korea, and other resistance mechanisms were commonly associated with 16S rRNA methylase- mediated resistance in Korea. (Korean J Clin Microbiol 2010;13:19-26)


16S rRNA dimethylase, armA, qnrB, Aminoglycoside, Gram-negative bacilli