Determination of trimethoprim-sulfamethoxazole resistance in Streptococcus pneumoniae by using the E test with Mueller-Hinton agar supplemented with sheep or horse blood may be unreliable. The Pneumococcal Study Group.
An international, multicenter study compared trimethoprim-sulfamethoxazole MICs for 743 Streptococcus pneumoniae isolates (107 to 244 isolates per country) by E test, using Mueller-Hinton agar supplemented with 5% defibrinated horse blood or 5% defibrinated sheep blood, with MICs determined by the National Committee for Clinical Laboratory Standards broth microdilution reference method. Agreement within 1 log2 dilution and minor error rates were 69.3 and 15.5%, respectively, on sheep blood-supplemented agar and 76.9 and 13.6%, respectively, with horse blood as the supplement. Significant interlaboratory variability was observed. E test may not be a reliable method for determining the resistance of pneumococci to trimethoprim-sulfamethoxazole.
Lovgren
M
M
National Centre for Streptococcus, Edmonton, Canada. ml@bugs.uah.ualberta.ca
Dell'Acqua
L
L
Palacio
R
R
Echániz-Aviles
G
G
Soto-Noguerón
A
A
Castañeda
E
E
Agudelo
C I
CI
Heitmann
I
I
Brandileone
M C
MC
Zanella
R C
RC
Rossi
A
A
Pace
J
J
Talbot
J A
JA
D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D001769:Blood; D003470:Culture Media; D018432:Drug Resistance, Multiple / Q000235:genetics; D005069:Evaluation Studies as Topic; D006736:Horses; D006801:Humans; D008826:Microbial Sensitivity Tests; D012756:Sheep; D013296:Streptococcus pneumoniae / Q000187:drug effects* / Q000302:isolation & purification; D013420:Sulfamethoxazole / Q000494:pharmacology; D014295:Trimethoprim / Q000494:pharmacology; D014296:Trimethoprim Resistance / Q000235:genetics
D000900:Anti-Bacterial Agents; D003470:Culture Media; D014295:Trimethoprim; D013420:Sulfamethoxazole