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Related Experiment Videos

Screening tests for pathogenic corynebacteria.

G Colman1, E Weaver, A Efstratiou

  • 1Diphtheria Reference Laboratory, Division of Hospital Infection, Colindale.

Journal of Clinical Pathology
|January 1, 1992
PubMed
Summary

Simple diagnostic tests can now efficiently identify toxigenic corynebacteria. Modified Elek tests and cystinase/pyrazinamidase assays accurately distinguish diphtheria toxin producers from non-producers.

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Area of Science:

  • Microbiology
  • Bacteriology
  • Diagnostic Microbiology

Background:

  • Diphtheria toxin-producing corynebacteria pose a significant public health risk.
  • Accurate and rapid identification of these pathogens is crucial for effective treatment and control.
  • Conventional diagnostic methods can be time-consuming and may lack sensitivity.

Purpose of the Study:

  • To develop and validate simple, efficient diagnostic tests for identifying diphtheria toxin-producing corynebacteria.
  • To improve upon existing methods for distinguishing pathogenic from non-pathogenic corynebacterial species.

Main Methods:

  • Conventional identification tests and an identification kit were used to characterize 99 corynebacterial isolates.
  • Modified procedures for the Elek test culture medium and pyrazinamidase activity detection were developed.
  • Cystinase activity, pyrazinamidase activity, and Elek test results were assessed on the bacterial collection.

Main Results:

  • Cystinase activity was exclusively detected in toxigenic species (61/61), while pyrazinamidase activity was found in non-toxigenic species (36/38).
  • Modified Elek tests showed positive results in 21/61 cystinase-positive, pyrazinamidase-negative cultures.
  • Guinea pig toxigenicity tests confirmed the accuracy of the plate tests, with modified Elek tests improving detection rates.

Conclusions:

  • The combination of cystinase, pyrazinamidase, and modified Elek tests provides an efficient method for distinguishing pathogenic corynebacteria.
  • These improved diagnostic procedures can aid clinical laboratories in accurately identifying diphtheria toxin producers.
  • The study highlights the limitations of conventional Elek tests and the benefit of optimized culture media.

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