Abstract
Streptococcus iniae is a bacterial pathogen that causes lesions and neurological damage in fish, and as a result, this pathogen is a
concern to fisheries. Isolates of streptococcus recovered from fish were examined and characterized using standard biochemical assays. Streptococcus iniae,
a β-hemolytic, non-Lancefield typeable streptococcus, is often misidentified due to an inadequate database. Moreover, biochemical tests typically used to
identify Streptococcus spp. are inappropriate for diagnosis of Streptococcus iniae strains. The atypical delayed hemolysis reaction on blood agar,
which many times cannot be detected until after 48 to 72 hours, can often be the first step in an inaccurate S. iniae diagnosis. This bacterium is
attracting attention due to recent human cases of cellulitis resulting from puncture wounds that occurred during the cleaning of fresh, whole fish.1,2
The human infection was treatable with β-lactam antibiotics. When the patients were surveyed, tilapia, a cultured food fish, was the most common species
associated with the cases. These human infections may not reflect the true prevalence, since identification of the bacteria is difficult. The hypothesis of this
study is the isolates from human cases are genetically similar to the Streptococcus iniae isolated from fish. The specific aim of this study was to
molecularly characterize both the human and fish isolates by Random Amplified Polymorphic DNA (RAPD) analysis and by polymerase chain reaction (PCR). Previously,
Weinstein typed isolates by pulsed-field gel electrophoresis(PFGE) and found that all of the human strains shared one PFGE pattern also observed in some of the
fish isolates.3 These particular fish isolates were given the designation as invasive clones that are capable of causing human infection. The RAPD and
PCR analyses conducted in this study showed evidence of genetic similarity between the fish and the human cases of S. iniae. The results from this study
suggest that the isolates of Streptococcus iniae from fish and human cases are genetically related.
References
1. 1996. Invasive Infection with Streptococcus iniae--Ontario, 1995-1996. Morbidity and Mortality Weekly Report.
45:650-653.
2. Weinstein M, D Low, A McGreer, et al. 1996. Invasive infection due to Streptococcus iniae: a new or previously
unrecognized disease--Ontario, 1995-1996. Canada Communicable Disease Report 22:129-132.
3. Weinstein M, M Litt, D Kertesz, et al. 1997. Invasive infections due to a fish pathogen, Streptococcus iniae.
New England Journal of Medicine 9:589-594.