DNase test as a novel approach for the routine screening of Corynebacterium diphtheriae (original) (raw)
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Screening for Corynebacterium diphtheriae
Journal of clinical …, 1992
A throat swab from a 9 year old girl with pharyngitis yielded a non-toxigenic strain of Corynebacterium diphtheriae var mitis and Streptococcus group G. C pseudodiphtheriticum was isolated from the throats oftwo ofher four brothers. In each case the isolate was sent to the reference laboratory before fill identification. The growth was found to be mixed for one brother; the other isolate being a toxin producing C diphtheriae var gravis. The child was asymptomatic and the case proves that all colonial types on the Hoyles plate should be identified.
Screening tests for pathogenic corynebacteria
Journal of Clinical Pathology, 1992
Aim: To provide simple tests that would help in the identification of corynebacteria that produce diphtheria toxin. Methods: A collection of 99 freshly isolated corynebacteria was assembled and the cultures identified by conventional tests confirmed by an identification kit. Modifications were made to procedures for preparation of the culture medium for the Elek test and to the test for detection of pyrazinamidase (pyrazine carboxylamidase) activity. These two together with an indicator medium for cystinase activity were applied to the collection of organisms. Results: Cystinase was detected in all 61 members of the toxigenic species and none produced pyrazinamidase. In contrast, all but two of the 38 representatives of non-toxigenic species yielded pyrazinamidase and none formed cystinase. Of the 61 cystinase producing cultures (which were also pyrazinamidase negative), 21 gave a positive Elek test with the modified culture medium. A total of 30 of these 61 were tested for toxigenicity in guinea pigs and the results of the animal and plate tests concorded. At least seven cultures could have been reported as nontoxigenic If Elek tests based on media prepared in the conventional way had Diphtheria Reference been the only test available. Laboratory, Division Conclusion: The three procedures desof Hospital Infection, cribed go some way towards meeting the Central Pubc Health needs of diagnostic laboratories for NW9 SHTfr efficient procedures for distinguishing G Colran pathogenic corynebacteria.
Journal of Clinical Pathology, 1994
Aims-To assess the performance of the polymerase chain reaction (PCR) when used to screen rapidly large numbers of corynebacteria for toxin production; and to determine the incidence of false positive PCR results with non-toxigenic Corynebacterium diphtheriae isolates. Methods-Eighty seven recent British isolates of corynebacteria were assayed by PCR. All isolates were assayed from both blood and telilurite agar within a five day period. Thirty three non-toxigenic isolates of C diphtheriae from six countries were also tested by PCR and by the Elek immunodiffusion assay. Results-There was complete concordance between the results of PCR and traditional methods on the recent British isolates, with one exception: an Elek positive "C ulcerans" isolate, which was PCR positive from tellurite but not from blood agar. One of the thirty three (3%) nontoxigenic isolates of C diphtheriae was PCR positive. Conclusions-These results suggest that PCR compares favourably with traditional methods for the detection of toxigenic corynebacteria and that it represents a powerful new tool in the diagnosis of an old disease.
Journal of Clinical Microbiology, 2003
One hundred two Corynebacterium diphtheriae strains (93 of the gravis biotype and nine of the mitis biotype) isolated from clinical cases during the Belarus diphtheria epidemic were characterized by biotyping, toxigenicity testing by the Elek test and an indirect hemagglutination assay, phage typing, and ribotyping. The gravis biotype strains were characterized as high and medium toxin producers, and strains of biotype mitis were characterized as low and medium toxin producers. Most strains (82 of 102) were distributed among five phage types. Seventy-two strains (64 of the gravis biotype and 8 of the mitis biotype) belonged to phage type VI ls5,34add. Hybridization of genomic DNA digested with BstEII and PvuII revealed five ribotype patterns, namely, D1, D4, D6, D7, and D13. The majority of gravis biotype strains belonged to ribotypes D1 (49 of 93) and D4 (33 of 93) and included one clonal group of C. diphtheriae. This clone predominated in all regions in Belarus. There was a statistical association between ribotypes and phage types but not between ribotypes and levels of toxin production.
Aerobic, Gram positive, catalase positive and non-spore forming bacilli, which are morphologically similar to Corynebacterium diphtheriae are described as either diphtheroids or coryneform bacteria, resembling C diphtheriae. Corynebacteria are a group of bacteria placed under the family corynebacteriaceae, which come under the phylum, Actinobacteria. Among the members of genus Corynebacterium, only C diphtheriae is considered as a pathogen but other species are present either as normal flora in human or as saprophytes in the environment and have rarely been associated with human infections. Of late, there have been increased reports of both new species of genus Corynebacterium and their occurrence in various human infections. It is now imperative that clinical microbiologists and clinicians understand the potential role of NDC in human infections. Only few studies globally have characterized the human clinical isolates of NDC and their antimicrobial susceptibility patterns. This review tries toexamine? the potential pathogenic nature of NDC, which warrants their identification and prompt reporting when isolated from human clinical specimens.
Journal of clinical microbiology, 1998
We have compared molecular, immunochemical, and cytotoxic assays for the detection of diphtheria toxin from 55 isolates of Corynebacterium diphtheriae and Corynebacterium ulcerans originally isolated in five different countries. The suitabilities and accuracies of these assays for the laboratory diagnosis of diphtheria were compared and evaluated against the "gold standard" in vivo methods. The in vivo and Vero cell cytotoxicity assays were accurate in their abilities to detect diphtheria toxin but were time-consuming; however, the cytotoxicity assay is a suitable in vitro alternative to the in vivo virulence test. There was complete concordance between all the phenotypic methods. Genotypic tests based upon PCR were rapid; however, PCR must be used with caution because some isolates of C. diphtheriae possessed toxin genes but failed to express a biologically active toxin. Therefore, phenotypic confirmation of toxigenicity for the microbiological diagnosis of diphtheria is ...
Molecular and Cellular Probes, 2008
The significant rise in the percentage of adults susceptible to diphtheria and the emergence of non-toxigenic Corynebacterium diphtheriae strains as the causative agent of endocarditis and other systemic infections emphasize the need for alternative laboratory diagnostic procedures. In this study, for the first time, the value of a species-specific PCR assay that targets the dtxR gene is documented as a procedure for differentiating C. diphtheriae from Corynebacterium-like colonies. The results of the PCR-dtxR were all positive for 91 C. diphtheriae (54 non-toxigenic and 37 toxigenic) strains. PCR-dtxR completely correlated with the standard biochemical and commercial identification for all C. diphtheriae strains tested. Conversely, the PCR-dtxR results were negative in 100% of the 111 non-diphtherial Gram-positive rod strains obtained during identification procedures in a hospital laboratory. Thus, the PCR-dtxR assay emerged as viable, cost-effective screening method for C. diphtheriae laboratory identification.