New turbidimetric assay for quantitation of viable bacterial densities

R. C. Li, D. E. Nix, J. J. Schentag

Research output: Contribution to journalComment/debatepeer-review

35 Scopus citations


A turbidimetric assay was developed and validated against Escherichia coli for the quantitation of viable bacterial densities. The Abbott MS-2 research system was employed for continuous 5-min measurements of optical density. A linear standard curve was obtained by regressing the initial bacterial density (log CFU per milliliter) against the time required for bacterial growth causing a 5% decrease in optical transmittance. Slope and intercept values obtained from eight standard curves showed excellent assay reproducibility. Results obtained by the turbidimetric assay compared favorably to those obtained by the conventional pour plate assay. Prior to the application of the new assay, possible interferences of postantibiotic effect induced by the test antibiotics were excluded. The turbidimetric assay, which is presumably more efficient and less expensive, was implemented for the time-kill studies of three different β-lactams against E. coli.

Original languageEnglish (US)
Pages (from-to)371-374
Number of pages4
JournalAntimicrobial Agents and Chemotherapy
Issue number2
StatePublished - 1993

ASJC Scopus subject areas

  • Pharmacology
  • Pharmacology (medical)
  • Infectious Diseases


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