1186. Substitutions in LiaFSR and Enzymes Involved in Glycerophospholipid Metabolism Correlate with High-Level DAP-Resistance in vivo in E. faecium
Session: Poster Abstract Session: Resistance Mechanisms
Friday, October 9, 2015
Room: Poster Hall
Background: We previously reported a patient with persistent bacteremia due to a DAP-susceptible Efm (HOU668) harboring mutations in liaSR (DAP MIC 3 ug/ml) who failed DAP therapy. The Efm strain exhibited a progressive increase in DAP and linezolid MICs (up to > 256 and 64 ug/ml, respectively) during the course of hospitalization. Despite this marked increase in DAP MIC, the isolate had no other mutations previously associated with DAP-R. In order of gain insights into the mechanisms of resistance of this isolate, we performed WGS of all Efm isolates sequentially obtained from the patient. 

Methods: A total of 5 sequential Efm isolates (HOU668, HOU672, HOU673, HOU676, HOU678) with increasing DAP MICs (3, 16, 24, 96 and 256 mg/L, respectively) were subjected to WGS on an Illumina platform. Single nucleotide polymorphisms (SNPs) were detected using the first isolate, HOU668 (DAP-S, MIC 3 mg/L) as reference for genomic comparisons. 

Results: The changes in LiaRS (T120A and W73C in LiaS and LiaR, respectively) persisted in all isolates. No changes were found in other 39 putative proteins previously associated with DAP-R in enterococci or staphylococci. A total of 13 genes harbored non-synonimous SNPs when compared to HOU668. Interestingly, the last two isolates, which exhibited the highest DAP MICs (96 and 256 mg/L, respectively), harbored changes in a predicted diacylglycerol kinase involved in the synthesis of glycerolphospholipids, not previously associated with DAP-R. Further, SNPs were detected in the upstream region of a gene coding for a predicted phosphatidylglyceroltransferase (PgsA homolog) and for an undecaprenyl diphosphate synthase. Finally, development of linezolid resistance in HOU676 and HOU678 (24 and 64 mg/L, respectively) was correlated with the G2576T mutation affecting 3 out of the 6 copies of the 23S rRNA gene. No evidence of cfr-carriage or further mutations in rlpC and rplD to explain the progressive increase in MIC were found.

Conclusion: Substitutions in the LiaFRS coupled with changes in glycerophospholipid metabolism are likely sufficient to confer high levels of DAP-R in vivo in E. faecium

Jose Munita, MD1,2, Rafael Rios, MSc3, Jinnethe Reyes, PhD3, Truc Tran, PhamD1, Diana Panesso, PhD1,3, Dylan Smith, BS3, Sandra Rincon, MSc3, Lina Paola Carvajal, BSc3, Juan David Garavito, BSc3, Mateo Castellanos, BSc3, Javier Adachi, MD, FIDSA4, Cesar Arias, MD, PhD, FIDSA1,3 and Lorena Diaz, PhD3, (1)University of Texas Medical School at Houston, Houston, TX, (2)Clinica Alemana - Universidad Del Desarrollo School of Medicine, Santiago, Chile, (3)Universidad El Bosque, Bogota, Colombia, (4)Dept. of Infectious Diseases, Infection Control and Employee Health, The University of Texas - MD Anderson Cancer Center, Houston, TX

Disclosures:

J. Munita, None

R. Rios, None

J. Reyes, None

T. Tran, None

D. Panesso, None

D. Smith, None

S. Rincon, None

L. P. Carvajal, None

J. D. Garavito, None

M. Castellanos, None

J. Adachi, Cubist (Merck): Grant Investigator , Research grant

C. Arias, Pfizer: Grant Investigator and Speaker's Bureau , Grant recipient and Speaker honorarium
Merck Sharp and Dohme: Grant Investigator and Speaker's Bureau , Grant recipient and Speaker honorarium
Cubist: Grant Investigator and Speaker's Bureau , Grant recipient and Speaker honorarium
Theravance: Grant Investigator and Speaker's Bureau , Grant recipient and Speaker honorarium
Bayer: Consultant , Consulting fee

L. Diaz, None

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