AdeABC-mediated efflux and tigecycline MICs for epidemic clones of Acinetobacter baumannii.
OBJECTIVE
Tigecycline non-susceptibility in individual Acinetobacter baumannii isolates has been associated with up-regulation of the resistance-nodulation-division (RND)-type efflux system, AdeABC. We sought to relate variation in the expression of this system to differences in modal tigecycline MIC among prevalent A. baumannii clones. The role of AdeABC in the emergence of tigecycline resistance during therapy was also investigated for two representatives of the prevalent UK lineage, OXA-23 clone 1.


METHODS
Clonal type was defined by PFGE and expression of adeABC by real-time RT-PCR. Laboratory mutants were selected in vitro by exposing a susceptible clinical isolate to increasing tigecycline concentrations. The adeB gene was inactivated by the directed integration of a suicide plasmid containing an internal fragment of the target gene.


RESULTS
Higher modal tigecycline MICs for particular clones correlated with elevated expression of adeABC. Expression of this operon was also increased in the two post-therapy, tigecycline-resistant clinical isolates and in a laboratory mutant as compared with their pre-exposure, tigecycline-susceptible counterparts. Interruption of adeB in a tigecycline-resistant clinical isolate restored full susceptibility to tigecycline.


CONCLUSIONS
Differences in expression of adeABC contribute to both inter- and intra-clone variation in tigecycline MICs. Tigecycline resistance can arise during therapy, mediated by up-regulation of AdeABC.
Hornsey
Michael
M
Antibiotic Resistance Monitoring and Reference Laboratory, Health Protection Agency Centre for Infections, 61 Colindale Avenue, London NW9 5EQ, UK. m.hornsey@qmul.ac.uk
Ellington
Matthew J
MJ
Doumith
Michel
M
Thomas
Claire P
CP
Gordon
Nicola C
NC
Wareham
David W
DW
Quinn
John
J
Lolans
Karen
K
Livermore
David M
DM
Woodford
Neil
N
D040981:Acinetobacter baumannii / Q000145:classification / Q000187:drug effects* / Q000302:isolation & purification / Q000378:metabolism; D000900:Anti-Bacterial Agents / Q000378:metabolism / Q000494:pharmacology*; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D015373:Bacterial Typing Techniques; D001692:Biological Transport; D016172:DNA Fingerprinting; D024881:Drug Resistance, Bacterial; D016521:Electrophoresis, Gel, Pulsed-Field; D020869:Gene Expression Profiling; D055786:Gene Knockout Techniques; D006801:Humans; D026901:Membrane Transport Proteins / Q000235:genetics / Q000378:metabolism*; D008826:Microbial Sensitivity Tests; D008911:Minocycline / Q000031:analogs & derivatives* / Q000378:metabolism / Q000494:pharmacology; D020133:Reverse Transcriptase Polymerase Chain Reaction; D000078304:Tigecycline; D006113:United Kingdom
C492436:AdeA protein, Acinetobacter baumannii; C445684:AdeB protein, Acinetobacter baumannii; C492437:AdeC protein, Acinetobacter baumannii; D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; D026901:Membrane Transport Proteins; D000078304:Tigecycline; D008911:Minocycline