JAC Advance Access published online on January 12, 2008
Journal of Antimicrobial Chemotherapy, doi:10.1093/jac/dkm498
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Reduction of disinfectant bactericidal activities in clinically isolated Acinetobacter species in the presence of organic material
1 Department of Medical Technology, Nagoya University Graduate School of Health Science, 1-1-20 Daiko Minami, Higashi-ku, Nagoya 461-8673, Japan 2 Department of Bacterial Pathogenesis and Infection Control, National Institute of Infectious Diseases, 4-7-1 Gakuen, Musashi-Murayama, Tokyo 208-0011, Japan
Received 30 July 2007; returned 15 October 2007; revised 27 November 2007; accepted 28 November 2007
* Corresponding author. Tel: +81-42-561-0771; Fax: +81-42-561-7173; E-mail: yarakawa{at}nih.go.jp
Objectives: In clinical Acinetobacter species, the reduction effects of organic material on bactericidal activities of four major disinfectants were investigated: chlorhexidine gluconate (CHX), benzethonium chloride (BZT), benzalkonium chloride (BZK) and alkyl diaminoethyl glycine hydrochloride (ADH).
Methods: The bactericidal activities of the four disinfectants against 283 strains of Acinetobacter species recovered from 97 Japanese hospitals in March 2002 were investigated by four different tests: MIC measurements, MBC measurements, time-killing assays and adaptation assays. Moreover, disinfectant efficacy was examined in the presence of BSA in two tests: MBC measurements and time-killing assays.
Results: No clinical isolates were able to withstand the in-use concentrations of the four disinfectants, although the MIC90 of ADH reached 100 mg/L. Strains for which MICs of at least two disinfectants were higher than MIC90 measured by the broth microdilution method were defined as isolates with ‘disinfectant reduced susceptibility (DRS)’. In the presence of 3.0% BSA, the MBCs of BZK, BZT and ADH for DRS isolates rose to 512 and 1024 mg/L, which were about half their in-use concentrations. Moreover, the times for bacterial complete killing were remarkably prolonged in DRS isolates even after a 10 min of exposure to 1000 mg/L of ADH, a half of its in-use concentration. The MICs of CHX for DRS isolates rose to 640 mg/L after repetitive passages in subinhibitory concentrations of CHX.
Conclusions: Given that the bactericidal effects of the four major disinfectants were considerably reduced in the presence of organic material (BSA) and DRS isolates tended to adapt to CHX, continuous surveys of the profiles of susceptibility to disinfectants among clinically isolated Acinetobacter species are very necessary from the standpoint of nosocomial infection control.
Key Words: susceptibility profiles , bovine serum albumin , adaptation