NONTOXIGENIC CORYNEBACTERIUM-DIPHTHERIAE BIOVAR GRAVIS - EVIDENCE FORAN INVASIVE CLONE IN A SOUTH-EASTERN AUSTRALIAN COMMUNITY

Objective: To determine the prevalence and clonality of non-toxigenic Corynebacterium diphtheriae biovar gravis in a community with two case s of endocarditis caused by this organism. Setting: A Koorie (Aborigin al) community in Gippsland, eastern Victoria, in 1994. Methods: Nose a nd throat swabs were collected from 359 community contacts of the case s and cultured for C. diphtheriae. Strains isolated from the contacts were compared by pulsed-field gel electrophoresis (after digestion wit h Sma1, Not1 and Sfi1) with those from the invasive cases in the same community, another invasive case in Victoria, a cluster of invasive ca ses in New South Wales (NSW) (1990-1991), and other stored strains iso lated from skin ulcers and sore throats. Results: Non-toxigenic strain s of C. diphtheriae biovar gravis were isolated from throat swabs of f ive of the case contacts. Uniform DNA patterns were found for the two community cases, the other Victorian case, nine of ten isolates from N SW, and the five throat isolates from case contacts. Conclusion: An in vasive clone of C. diphtheriae biovar gravis appears to have been resp onsible for the three Victorian cases of endocarditis. It was also pre sent among case contacts and responsible for previous invasive cases i n NSW. Prophylactic treatment should be considered for clearly defined contacts in all instances where C. diphtheriae is isolated from a nor mally sterile site, regardless of the toxigenic nature of the strain.