Simple inoculum standardizing system for antimicrobial disk susceptibility tests

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Abstract
A collaborative study was undertaken to evaluate a simple, convenient device which expedites inoculum standardization for antimicrobial disc susceptibility tests. The Inocupac system (Minnesota Mining and Manufacturing [3M] Co., St. Paul, Minnesota, USA) was used to perform disc tests in parallel with the standard Bauer-Kirby method. Five investigators tested 100 selected isolates, each in triplicate. Inter- and intralaboratory precision of both disc procedures was essentially comparable. The Inocupac system failed to consistently provide satisfactory growth with some streptococci, but when testing common gram-negative bacilli, staphylococci and most enterococci, the Inocupac system gave zones about the same size (.+-. 2 mm) as the Bauer-Kirby procedure. Interpretive agreement between the 2 test systems varied from 90-99% with different antimicrobial agents, and repeated tests with the Bauer-Kirby method demonstrated the same degree of interpretive agreement. The Inocupac system is a valid alternative method for inoculating disc susceptibility tests.