For microbiologic and epidemiologic surveillance, it is crucial that the laboratory receive the following information for each specimen from suspected cases, contacts, and carriers: name, age, and sex of patient; hospital to which the patient was admitted; name of physician caring for the patient; laboratory details (source of specimen, date collected); clinical details (symptoms, onset date, treatment regime); epidemiologic information (case, contact, or carrier); and immunization and travel histories.
Screening tests for presumptive identification
Unless a clinical diagnosis of diphtheria is suspected, laboratory diagnosis may be difficult because C. diphtheriae is not easily identified on blood agar. In addition, swabs with specimens from asymptomatic carriers or contacts may contain only small numbers of organisms, which may be obscured by the overgrowth of normal throat flora. To obtain the better results all the swabs are investigated using the tellurite medium.
Clinical specimens should ideally be cultured onto blood agar and selective tellurite media; Hoyle's tellurite medium is recommended . Tellurite medium enhances the growth of the diphtheria bacteria and reduces the growth of normal flora.
Significance of biotyping:
Pathogenic strains can be easily identified by the use of simple tests such as API CORYNE and Rosco diagnostics tests are readily available. They shows pyrazinamidase negative, and cystinase positive. They will also ferment glucose, maltose, and starch. They also shows catalase and nitrate positive, urease negative.
Elk Gel Precipitation test:
A strip of filter paper is impregnated with diphtherial antitoxin is buried just beneath the surface of the special agar plate before the agar hardens. Strains should be tested are streaked with known positive and known negative toxigenic strains on the agar’s surface in a line across the plate and at right angles to the antitoxin paper strip. After incubation for 24 hours at 37 degree Celsius plates are examined with transmitted light for the presence of fine precipitin lines at a 45 degree angle to the streaks.
Polymerase chain reaction:
This uses the amplification of the DNA of the bacteria which is in investigation.