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Antimicrob Agents Chemother. 2017 Jul 25;61(8). pii: e00391-17. doi: 10.1128/AAC.00391-17. Print 2017 Aug.

Roles of ramR and tet(A) Mutations in Conferring Tigecycline Resistance in Carbapenem-Resistant Klebsiella pneumoniae Clinical Isolates.

Author information

1
Division of Infectious Diseases and Tropical Medicine, Department of Internal Medicine, Tri-Service General Hospital, National Defense Medical Center, Taipei, Taiwan, Republic of China.
2
Graduate Institute of Medical Sciences, National Defense Medical Center, Taipei, Taiwan, Republic of China.
3
Institute of Infectious Diseases and Vaccinology, National Health Research Institutes, Miaoli, Taiwan, Republic of China.
4
Graduate Institute of Microbiology and Immunology, National Defense Medical Center, Taipei, Taiwan, Republic of China.
5
Graduate Institute of Basic Medical Science, China Medical University, Taichung, Taiwan, Republic of China.
6
Division of Infectious Diseases and Tropical Medicine, Department of Internal Medicine, Tri-Service General Hospital, National Defense Medical Center, Taipei, Taiwan, Republic of China kmyeh@ndmctsgh.edu.tw.

Abstract

Tigecycline is regarded as a last-resort treatment for carbapenem-resistant Klebsiella pneumoniae (CRKP) infections, but increasing numbers of tigecycline-resistant K. pneumoniae isolates have been reported. The tigecycline resistance mechanisms in CRKP are undetermined. This study aimed to elucidate the mechanisms underlying tigecycline resistance in 16 tigecycline- and carbapenem-resistant K. pneumoniae (TCRKP) isolates. Mutations in tigecycline resistance determinant genes [ramR, acrR, oqxR, tet(A), tet(L), tet(X), tet(M), rpsJ] were assessed by PCR amplicon sequencing, and mutations in ramR and tet(A) exhibited high prevalences individually (81%) and in combination (63%). Eight functional ramR mutation profiles reducing tigecycline sensitivity were verified by plasmid complementation of wild-type and mutant ramR Using a site-specific mutant, the most frequent RamR mutation, A19V (60%), had no significant effect on tigecycline susceptibility or the upregulation of ramA and acrA Two tet(A) variants with double frameshift mutations, type 1 and type 2, were identified; type 2 tet(A) is novel. A parent strain transformed with a plasmid carrying type 1 or type 2 tet(A) increased the tigecycline MIC by 8-fold or 4-fold, respectively. Synergistic effects were observed in strains harboring no ramR gene and a mutated tet(A), with an 8-fold increase in the tigecycline MIC compared with that in strains harboring only mutated tet(A) being seen. Overall, mutations in the ramR and tet(A) efflux genes constituted the major tigecycline resistance mechanisms among the studied TCRKP isolates. The identification of strains exhibiting the combination of a ramR deficiency and widespread mutated tet(A) is concerning due to the possible dissemination of increased tigecycline resistance in K. pneumoniae.

KEYWORDS:

Klebsiella pneumoniae; ramR; tet(A); tigecycline resistance

PMID:
28533243
PMCID:
PMC5527587
DOI:
10.1128/AAC.00391-17
[Indexed for MEDLINE]
Free PMC Article

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