JAC Advance Access published online on October 29, 2003
Journal of Antimicrobial Chemotherapy, doi:10.1093/jac/dkg462
© 2003 by The British Society for Antimicrobial Chemotherapy
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Original article
1 GR Micro Ltd, 7-9
William Road, London NW1 3ER, UK
* Corresponding author. E-mail: rosy.reynolds{at}btinternet.com.
Received 1 July 2003
; revised 26 August 2003
; accepted 28 August 2003
Objective: The aim of this study was
to establish the degree of comparability between the NCCLS broth microdilution
and BSAC agar dilution MIC methods of antimicrobial susceptibility
testing. Methods: Six hundred and sixty-one clinical
isolates of Streptococcus pneumoniae, 936 Haemophilus influenzae and
421 Moraxella catarrhalis, collected in the winter
of 1999-2000 by 20 laboratories in the UK and Eire from
patients with presumed community-acquired lower respiratory infections,
were tested by the two methods. MIC agreement was defined as excellent
(good) if results were within ±1 doubling
dilution for Results: MIC agreement was good or excellent
in 27 of 36 organism-agent combinations. Agreement was less
for M. catarrhalis than for other species, and
lower in all three species for cefaclor and trimethoprim than for
other antimicrobials. Discrepancies in categorization occurred only
occasionally, and were generally explained by differences in breakpoints
rather than in measured MICs. One exception was S. pneumoniae with
penicillin. Despite excellent MIC agreement and identical breakpoints,
9% of these had minor discrepancies, mainly because 7% of
isolates were found intermediate by the BSAC method but resistant
by the NCCLS method. Conclusion: There is generally very good agreement
between the MICs obtained by the BSAC agar dilution and NCCLS broth
microdilution methods in this population of isolates, comparable
to the level of agreement achieved between different laboratories
using a single method. Breakpoint differences contribute to most
of the discrepancies in susceptibility categorization.
Keywords: methodology, antimicrobial susceptibility, respiratory
pathogens
Comparison of BSAC agar dilution and NCCLS broth
microdilution MIC methods for in vitro susceptibility
testing of Streptococcus pneumoniae, Haemophilus
influenzae and Moraxella catarrhalis: the BSAC
Respiratory Resistance Surveillance Programme
2 Department of Medical
Microbiology, North bristol NHS Trust, Southmead Hospital, Bristol
BS10 5NB;
90% (80%)
of isolates and within ±2 doubling dilutions
for 95%. Isolates were categorized
as susceptible, intermediate or resistant using the breakpoints
appropriate to the testing method.
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