Detection of toxin production by Corynebacterium diphtheriae: results of a trial organised as part of the United Kingdom National External Microbiological Quality Assessment Scheme.

Abstract

SUMMARY Four strains of Corynebacterium diphtheriae were sent to UK participants in the UK National External Microbiological Quality Assessment Scheme, who were asked to examine the strains for toxin production by in vitro methods. Laboratories achieved 162/176 (92%) and 160/175 (91 %) correct results with two rapid toxin producers and 145/175 (82%) with a slow toxin producer. With a non-toxigenic strain 26/175 (15%) laboratories reported toxin production. Of the 173 laboratories reporting on all four strains, only 120 (69%) achieved the correct result for all. There was no significant association between the use of various methods and results, with the exception that laboratories using a full set of positive, weak positive, and negative controls made fewer errors than those not using controls. A number of unsatisfactory practices were revealed by the trial, however, and recommendations on preparation of inoculum, media, peptones, animal sera, and use of controls are made.The United Kingdom National External Microbiological Quality Assessment Scheme has been described previously.' As part of the bacteriology portion of this scheme simulated specimens containing various pathogens are distributed to participants. Although most of these pathogens occur commonly in the UK, rarer but important pathogens are occasionally distributed for educational purposes. C diphtheriae has been distributed on a number of occasions with an average success rate in isolation and identification of 85%. No systematic information had been sought on toxigenicity testing of these strains, and in view of the continued occurrence of this species in the UK2 the Public Health Laboratory Service thought it would be useful to investigate the ability of laboratories to demonstrate toxin production in the event of another outbreak.

A modified Elek test for detection of toxigenic corynebacteria in the diagnostic laboratory

“…Discs were dried at 37ЊC for 1 h and used to determine the effect of antitoxin concentration on the detection of toxigenicity. Plates were inoculated at various distances (3,6,9,12, and 15 mm) from the edge of the antitoxin disc (10 IU/disc) with a light, medium, or heavy inoculum to determine the effects of density and distance of inocula on detection of toxigenicity.…”

Reversed passive latex agglutination assay for detection of toxigenic Corynebacterium diphtheriae

“…Even if the technique is standardized, the test is technically demanding and needs to be rigidly quality controlled. Furthermore, a microbiological quality assessment trial for examining toxin production by in vitro methods showed that only 69% of the laboratories achieved the correct result (23). The large amount of effort needed to ensure satisfactory results with the Elek test suggests the necessity of a simple and reliable in vitro method for DT detection.…”

The Use of Lodging Ratios in Tourism. Juanita C. Liu and Turgut Var. Annals of Tourism Research, vol. 7, no. 3, 1980, pp. 406-427. Department of Habitational Resources, University of Wisconsin-Stout, Menomonie, Wisconsin 54751. $7.50

“…Currently, the only in vitro method readily available to the majority of diagnostic laboratories is the Elek immunoprecipitation test, first described in 1949, which is both technically demanding and prone to misinterpretation (2). Difficulties with the application of the Elek test have been reported (12): in a United Kingdom national external quality assessment scheme conducted in 1984, only 69% (120 of 173) of participating laboratories obtained the correct result for all four strains of C. diphtheriae distributed. Although the clarity and accuracy of the test have been improved following the modification of the Elek medium (1), the misinterpretation of nonspecific precipitin lines remains common, particularly in laboratories where the test is performed infrequently.…”

“…Discs were dried at 37ЊC for 1 h and used to determine the effect of antitoxin concentration on the detection of toxigenicity. Plates were inoculated at various distances (3,6,9,12, and 15 mm) from the edge of the antitoxin disc (10 IU/disc) with a light, medium, or heavy inoculum to determine the effects of density and distance of inocula on detection of toxigenicity.…”