Comparison of direct and standard antimicrobial disk susceptibility testing for bacteria isolated from blood.


Journal Article

To determine the reliability of early antimicrobial susceptibility testing, we compared the results of direct and standard single-disk diffusion methods for 581 positive blood cultures processed routinely by the clinical microbiology laboratory. The direct procedure differed from the standard one only in that the 0.5 McFarland inoculum was prepared from 1 ml of turbid broth rather than five isolated colonies from a subculture plate. A major discrepancy in results was defined as a change from susceptible to resistant or vice versa according to interpretive standards for zone diameters, whereas a minor discrepancy was defined as a shift to or from the intermediate category when paired direct and standard tests were compared. The overall agreement between the two methods was 94.6% of 2,308 comparisons. There were 119 minor (5.2%) and 6 major (0.3%) discrepancies. The major discrepancies were seen with three strains of Staphylococcus epidermidis and one strain each of S. aureus, Escherichia coli, and Enterobacter sp. Direct susceptibility testing of positive blood cultures that were pure by gram-stained smear provided reliable results 24 to 36 h earlier than conventional procedures; therefore, we recommended this procedure to guide early antimicrobial therapy in patients with bacterial sepsis.

Full Text

Duke Authors

Cited Authors

  • Mirrett, S; Reller, LB

Published Date

  • October 1, 1979

Published In

Volume / Issue

  • 10 / 4

Start / End Page

  • 482 - 487

PubMed ID

  • 528681

Pubmed Central ID

  • 528681

International Standard Serial Number (ISSN)

  • 0095-1137

Digital Object Identifier (DOI)

  • 10.1128/JCM.10.4.482-487.1979


  • eng

Conference Location

  • United States