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Imipenem heteroresistance induced by imipenem in multidrug-resistant Acinetobacter baumannii: mechanism and clinical implications.

Abstract：

:Acinetobacter baumannii has emerged as a major pathogen causing nosocomial infections, particularly in critical patients admitted to the Intensive Care Unit. Increasing resistance to carbapenems in A. baumannii has been observed worldwide. Here we report the clinical impact and mechanism of imipenem heteroresistance (imipenem minimum inhibitory concentration of 6-32 μg/mL with the presence of resistant cells inside the inhibition zone of Etest strips or disks) in multidrug-resistant A. baumannii (MDR-AB). To identify risk factors associated with the emergence of imipenem heteroresistance, a retrospective case-control study was undertaken involving cases with subsequent clinical isolates of the same genotype showing loss of imipenem susceptibility and matched controls with isolates belonging to imipenem-susceptible MDR-AB. The molecular mechanism of heteroresistance was examined. From April 2006 to March 2007, 126 consecutive isolates of MDR-AB were identified from 29 patients. Switch from imipenem susceptibility to heteroresistance was more likely to occur in successive MDR-AB derived from patients who had been exposed to imipenem (length of use 10.9 ± 6.5 days for cases vs. 5.3 ± 4.8 days for controls; P=0.02). An insertion sequence (ISAba1) was found in the promoter region of a class C β-lactamase gene (bla(ADC-29)) in most imipenem-heteroresistant MDR-AB isolates. In vitro experiments indicated that imipenem heteroresistance, which was associated with overexpression of bla(ADC-29), could be induced by imipenem. Carbapenem use was the only risk factor identified for the emergence of carbapenem-heteroresistant MDR-AB. Physicians should weigh the benefits and risks of each carbapenem-based treatment in managing carbapenem-susceptible MDR-AB infection.

journal_name

Int J Antimicrob Agents

journal_title

International journal of antimicrobial agents

authors

Lee HY,Chen CL,Wang SB,Su LH,Chen SH,Liu SY,Wu TL,Lin TY,Chiu CH

doi

10.1016/j.ijantimicag.2010.12.015

subject

Has Abstract

pub_date

2011-04-01 00:00:00

pages

302-8

issue

eissn

0924-8579

issn

1872-7913

pii

S0924-8579(11)00036-7

journal_volume

pub_type

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Imipenem heteroresistance induced by imipenem in multidrug-resistant Acinetobacter baumannii: mechanism and clinical implications.