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Antimicrobial Agents and Chemotherapy, Jan 1997, 129-134, Vol 41, No. 1
EL Fasola, S Bajaksouzian, PC Appelbaum and MR Jacobs
Susceptibilities of 124 strains of Streptococcus pneumoniae to erythromycin
and clindamycin were determined by the National Committee for the Clinical
Laboratory Standards (NCCLS) broth microdilution method, with incubation
for 20 to 24 h in ambient air and with modifications of this method by
incubation for up to 48 h in air and CO2. Strains were also tested by agar
dilution, E-test, and disk diffusion; good correlation was obtained with
these methods, with clear separation into bimodal populations of
susceptible and resistant stains. The broth microdilution method, however,
using incubation in air for 24 h (NCCLS method), misclassified 4 of 92
erythromycin- resistant strains (1 as susceptible and 3 as intermediate)
and 25 of 58 clindamycin-resistant strains (all as susceptible). With the
exception of one strain with clindamycin, susceptible and resistant strains
were correctly classified by the microdilution method with incubation in
CO2 for 24 h or in ambient air for 48 h. Disk diffusion, agar dilution, and
E-test methods with incubation in 5% CO2 are therefore reliable methods for
susceptibility testing of pneumococci against these agents. However, the
NCCLS microdilution method, which specifies incubation for 20 to 24 h in
ambient air, produced significant very major errors (43%) clindamycin.
Modification of the microdilution method by incubation in 5% CO2 or by
extension of incubation time in ambient air to 48 h corrected these errors.
Disk diffusion, however, was shown to be a simple, convenient, and reliable
method for susceptibility testing of pneumococci to erythromycin and
clindamycin and is suggested as the method of choice for these agents.
Copyright © 1997 by the American Society for Microbiology. All rights reserved.
Variation in erythromycin and clindamycin susceptibilities of Streptococcus pneumoniae by four test methods
Department of Pathology, Case Western Reserve University, Cleveland, Ohio, USA.
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