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Journal of Clinical Microbiology, May 2007, p. 1640-1643, Vol. 45, No. 5
0095-1137/07/$08.00+0     doi:10.1128/JCM.00143-07
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

Reevaluation of Clinical and Laboratory Standards Institute Disk Diffusion Breakpoints for Tetracyclines for Testing Enterobacteriaceae

JMI Laboratories, North Liberty, Iowa,¹ Massachusetts General Hospital, Boston, Massachusetts,² Duke University, Durham, North Carolina,³ Loyola University Chicago, Chicago, Illinois,⁴ CDC, Atlanta, Georgia⁵

Received 19 January 2007/ Returned for modification 11 February 2007/ Accepted 2 March 2007

We reevaluated Enterobacteriaceae disk diffusion breakpoints for the tetracyclines published in the Clinical and Laboratory Standards Institute (CLSI) document M100-S16, which were (susceptible/resistant) 19 mm/14 mm for tetracycline, 16 mm/12 mm for doxycycline, and 19 mm/14 mm for minocycline. A collection of 504 recent clinical isolates of Enterobacteriaceae were tested against these tetracycline compounds by disk diffusion and broth microdilution methods according to CLSI guidelines. Regression line and scattergram plot analyses determined intermethod accuracy for current disk diffusion breakpoints and showed excellent r values of 0.91 to 0.95. However, error rates (minor/major [false-resistant]/very major [false-susceptible]) were 14.9/0.8/0.0% for tetracycline, 11.5/0.4/0.0% for doxycycline, and 30.6/0.7/0.0% for minocycline and only 4.4/0.0/0.0% for tetracycline, 5.6/0.0/0.2% for doxycycline, and 8.3/0.0/0.3% for minocycline when proposed breakpoints were modified to (susceptible/resistant) 15 mm/11 mm for tetracycline, 14 mm/10 mm for doxycycline, and 16 mm/12 mm for minocycline. Listed modifications were recently approved by the CLSI (M100-S17).

Published ahead of print on 14 March 2007.