Rapid Virulence Test in Diagnosis of Diphtheria

Abstract

Summary The mixed growth from 266 original Loeffler slants submitted for diagnosis of suspected diphtheria was streaked directly onto tellurite-agar plates prepared for the in vitro toxigenicity test (I.V.T.T.). Of 196 such diagnostic specimens later shown, by pure culture isolations and animal tests, to contain virulent C. diphtheriae, 130 (66.3%) yielded positive results; 63 (48%) in 24 hours, 53 (40%) in 48 hours and 14 (11%) in 72 hours. Nine of the original 266 cultures were later shown by pure culture isolations and animal tests to contain non-toxigenic C. diphtheriae. These yielded negative I.V.T.T. Preliminary tests with prepared swabs indicate that positive I.V.T.T. frequently may be obtained directly from them in 24 hours. The I.V.T.T. plate, with K Te, offers a rapid and simple method of detecting virulent C. diphtheriae in a useful percentage of original diagnostic specimens.