Recovery of Streptococcus iniae from Diseased Fish Previously Vaccinated with a Streptococcus Vaccine

Abstract

Streptococcus iniae was recovered from diseased rainbow trout (Oncorhynchus mykiss, Walbaum) previously vaccinated against streptococcosis. PCR and serological methods indicate the presence of a new serotype in the diseased fish.The fish pathogen Streptococcus iniae (11) is endemic in various parts of the world, including Israel (6) and North America (10). S. iniae infection of rainbow trout (Oncorhynchus mykiss) produces a disease which substantially affects the brain, with only minor pathological changes in other organs (4). Recently, S. iniae has been isolated from diseased humans suffering from cellulitis, meningitis, and bacteremias, indicating a threat to public health (16).A specific S. iniae vaccine became available in 1995. From 1995 to 1997, all Israeli trout farms in the Upper Galilee, (which share water reservoirs) routinely vaccinated their entire stocks (roughly 3 million fish/year), reducing S. iniae-related mortalities from 50% annually to less than 5% (5). However, massive new outbreaks of the disease were recorded in 1997. Unlike the previous pathological manifestations, diseased fish exhibited multisystem organ involvement and diffuse internal hemorrhages. Brains samples were collected from diseased fish and streaked on Columbia agar base (Difco) supplemented with 5% (vol/vol) defibrinated sheep blood. Beta-hemolytic gram-positive cocci were detected following an incubation of 24 to 48 h at 24°C. Conventional identification schemes (API 20 STREP; BioMerieux SA, Marcy l'Etoie, France) suggested that all isolates (of 100 collected over 24 months) were S. iniae. The new isolates, unlike the previous isolates, were shown to be arginine dehydrolase (ADH) negative. Definitive identification was accomplished by PCR, using S. iniae 16S rDNAspecific primers (Zlotkin et al. [17]), which revealed the 300-bp S. iniae-specific PCR product in all isolates.Six (11)). The rDNA sequence analyses confirmed that the six isolates were S. iniae. All had an identical sequence (GenBank accession no. AF335573) and differed from that of S. iniae ATCC 29178 (GenBank accession no. AF335572) in six bases (99.6% homology). EcoRI and HindIII digests of DNAs extracted from early and recent isolates resulted in identical restriction fragment length polymorphism ribotype patterns (data not shown), indicating that all isolates cluster in the Israeli S. iniae rank (6). The use of additional endonucleases (PvuII or KpnI) did not provide strain-to-strain differentiation (data not shown).The random amplified polymorphic DNA (RAPD) technique ( Fig. 1) was used to distinguish early from recent isolates. Primer p14 (5ЈGATCAAGTCC), previously proven useful for discrimination among group A streptococcol strains, was used (Neeman et al. [8]). All early (1991 to 1995) isolates produced a band with an estimated length of 750 bp. No such band was found in the PCR product of the recent isolates (Fig. 1).Hyperimmune sera for serological differentiation were obtained by three monthly immunizations of rainbow trout with formalin-fixed S. inia...

Yersinia ruckeri biotype 2 isolates from mainland Europe and the UK likely represent different clonal groups

“…Strain replacement in response to continuous immunisation selective pressure has been reported for other fish pathogens (Bachrach et al 2001) and medically important bacteria (e.g. Urwin et al 1996, Spratt & Greenwood 2000, Hallander et al 2005).…”

Serological Characterization of Streptococcus iniae Strains Isolated from Cultured Fish in Japan

“…There are several reports concerning the diversity of S. iniae strains in biochemical characteristics (Pier et al, 1978;Sakai et al, 1993;Stoffregen et al, 1996;Dodson et al, 1999), genomic structure (Eldar et al, 1997;Fuller et al, 2001) and serological properties (Pier et al, 1978;Klesius et al, 2000;Bachrach et al, 2001;Barnes et al, 2003). In the present study, though genomics were not investigated, the two serological types were indistinguishable by any biochemical tests performed.…”

“…However, for S. iniae this has scarcely been conducted so far, except that Pier et al (1978) demonstrated group and strain-specific antigens in cellextracts and that Eldar et al (1997) investigated the antigen recognition by sera of vaccinated fish. Recently Bachrach et al (2001) and Barnes et al (2003) reported the second serotype of S. iniae derived from diseased fish in Israel and USA.…”

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

“…There are 2 serotypes of Streptococcus iniae. A previous study has shown that infection with serotype I S. iniae tends mainly to cause neural lesions, while infection with serotype II S. iniae predominately induces systemic inflammation, affecting multiple organs with diffuse internal haemorrhages (Bachrach et al 2001). We found that the S. iniae-infected channel catfish displayed systemic inflammation, which suggests that the pathogen is likely to be serotype II of S. iniae.…”