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Canadian Journal of Infectious Diseases
Volume 3 (1992), Issue 4, Pages 193-201

Subinhibitory Antimicrobial Concentrations: A Review of In Vitro and In Vivo Data

George G Zhanel,1,2 Daryl J Hoban,1 and Godfrey KM Harding1,2

1Department of Medical Microbiology, Faculty of Medicine and Faculty of Pharmacy, University of Manitoba, Winnipeg, Manitoba, Canada
2Health Sciences Centre, St Boniface General Hospital and St Boniface General Hospital Research Centre, Winnipeg, Manitoba, Canada

Received 27 July 1990; Accepted 23 March 1991

Copyright © 1992 Hindawi Publishing Corporation. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


Antimicrobial activity is not an ‘all or none’ effect. An increase in the rate and extent of antimicrobial action is usually observed over a wide range of antimicrobial concentrations. Subinhibitory antimicrobial concentrations are well known to produce significant antibacterial effects, and various antimicrobials at subinhibitory concentrations have been reported to inhibit the rate of bacterial growth. Bacterial virulence may be increased or decreased by subinhibitory antimicrobial concentrations by changes in the ability of bacteria to adhere to epithelial cells or by alterations in bacterial susceptibility to host immune defences. Animal studies performed in rats, hamsters and rabbits demonstrate decreased bacterial adherence, reduced infectivity and increased survival of animals treated with subinhibitory antimicrobial concentrations compared to untreated controls. The major future role of investigation of subinhibitory antimicrobial concentrations will be to define more fully, at a molecular level, how antimicrobials exert their antibacterial effects.