Reduction of disinfectant bactericidal activities in clinically isolated Acinetobacter species in the presence of organic material

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, disin-fectant 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 ‘disinfec-tant 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 isolate