Invasive Streptococcus iniae Infections Outside North America

Abstract

Streptococcus iniae, a fish pathogen causing infections in aquaculture farms worldwide, has only been reported to cause human infections in North America. In this article, we report the first two cases of invasive S. iniae infections in two Chinese patients outside North America. While the first patient presented with bacteremic cellulitis, which is the most common presentation in previous cases, the second patient represents the first recognized case of S. iniae osteomyelitis. Both S. iniae strains isolated from the two patients were either misidentified or unidentified by three commercial systems and were only identified by 16S rRNA gene sequencing. Since no currently available commercial system for bacterial identification includes S. iniae in its database, 16S rRNA gene sequencing is the most practical and reliable method to identify the bacterium at the moment. In contrast to the distinct genetic profile described previously in clinical isolates from Canada, the present two isolates and a clinical isolate from a Canadian patient were found to be genetically unrelated, as demonstrated by pulsed-field gel electrophoresis. Morphologically, colonies of both isolates were also larger, more beta-hemolytic and mucoid, which differ from the usual morphotype described for S. iniae. Owing to their habit of cooking and eating fresh fish, the Asian population is strongly associated with S. iniae infections. As a result of the difficulty in making microbiological diagnosis in patients with cellulitis and the problem of identification in most clinical microbiology laboratories, the prevalence of S. iniae infections, especially in the Asian population, may have been under-estimated.

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“…In rainbow trout, streptococcosis is characterized by a subacute to acute course, with specific lesions of panophthalmitis and meningitis beside minor pathological changes in other organs (Eldar and Ghittino, 1999). Moreover, S. iniae has recently emerged as a threat to public health due to its zoonotic importance, being isolated from humans infected due to accidental injuries during handling of fresh infected fish (Weinstein et al, 1997;Lau et al, 2003;Koh et al, 2004;Facklam et al, 2005;Lau et al, 2006 andSun et al, 2007). Candida albicans (C. albicans) is an opportunistic fungal pathogen that normally inhabits the digestive tract and mucosal regions of mammals and birds.…”

The novel polysaccharide deacetylase homologue Pdi contributes to virulence of the aquatic pathogen Streptococcus iniae

“…In addition, S. iniae has established itself as a zoonotic risk, especially in areas of the world that preferentially prepare and consume raw fish (Lau et al, 2003). To date, at least 25 human cases of invasive streptococcal infection attributed to S. iniae have been confirmed in the USA, Canada, China and Taiwan, many of which were in immunocompromised patients (Agnew & Barnes, 2007;Sun et al, 2007;Weinstein et al, 1997); since there is currently no prospective epidemiological surveillance for human S. iniae infections, the true number may be much higher (Facklam et al, 2005;Lau et al, 2006).…”

Pathological changes in cultured channel catfish Ictalurus punctatus spontaneously infected with Streptococcus iniae

“…In barramundi Lates calcarifer, S. iniae infection induces systemic and necrotizing inflammation (Creeper & Buller 2006) and, in tilapia, meningoencephalitis and pa noph thalmitis (Eldar et al 1995). Interestingly, a few studies have shown that S. iniae infection causes bacteremic cellulitis in humans (Lau et al 2003, Facklam et al 2005. The range of different diseases caused by S. iniae infection can be attributed to the variety of host species and to environmental factors.…”