Volume 24-22
15 November 1998

[Table of Contents]

Strain Characteristics of Streptococcus iniae Isolated from Tilapia Species in Vancouver, British Columbia

Following the 1995-1996 Toronto epidemic of human infection with Streptococcus iniae in patients handling fresh whole fish^(1,2), an epidemiologic and microbiologic study was initiated to determine the possibility of S. iniae carriage on Vancouver's fresh fish. Eleven tilapia fish and six other species sharing circulated tank water and purchased live from five fish markets in the Greater Vancouver Regional District, British Columbia, were swabbed and cultured for S. iniae on sheep blood agar and colistin-nalidixic acid medium. Seven out of 11 tilapia and four out of six other fish (rock cod, trout, sculpin) were culture positive by standard microbiologic methods. Pulsed-field gel electrophoresis (PFGE) using restriction endo- nucleases SmaI and ApaI revealed that Vancouver's S. iniae strain was identical to the epidemic strain of human isolates and some, but not all, of the fish isolates from Toronto. In 1997, a Vancouver surveillance identified two cases of human cellulitis and bacteremia caused by S. iniae in patients who sustained inoculation injuries while preparing tilapia. In both cases, the S. iniae strain was identical to the Toronto outbreak strain identified by PFGE. Whereas fish farms supplying Toronto markets were located in Tennessee, Arkansas, North Dakota, Delaware, and Illinois, the Vancouver tilapia were traced to a fish farm in North Dakota which does not supply Toronto. Our results suggest that a single clone of S. iniae has caused disease in geographically remote regions which may or may not be related to a common source, and that this strain may contain a virulence factor which is important for pathogenicity in humans and fish.

References

1. 1. Weinstein MR, Low DE, Litt M et al. Invasive infections due to a fish pathogen, Streptococcus iniae. N Engl J Med 1997;337:589-94.

2. 2. Weinstein MR, Low DE, McGeer A et al. Invasive infection due to Streptococcus iniae: a new or previously unrecognized disease - Ontario, 1995-1996. CCDR 1996;22:129-32.

Source: N Press, MD, E Bryce, MD, G Stiver, MD, Division of Infectious Diseases and Department of Medical Microbiology, University of British Columbia, Vancouver BC.

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