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Bell S.C.,James Cook University | Alford R.A.,James Cook University | Garland S.,James Cook University | Padilla G.,University of Sao Paulo | Thomas A.D.,Tropical and Aquatic Animal Health Laboratory
Diseases of Aquatic Organisms

Certain bacteria present on frog skin can prevent infection by the pathogenic fungus Batrachochytrium dendrobatidis (Bd), conferring disease resistance. Previous studies have used agar-based in vitro challenge assays to screen bacteria for Bd-inhibitory activity and to identify candidates for bacterial supplementation trials. However, agar-based assays can be difficult to set up and to replicate reliably. To overcome these difficulties, we developed a semi-quantitative spectrophotometric challenge assay technique. Cell-free supernatants were prepared from filtered bacterial cultures and added to 96-well plates in replicated wells containing Bd zoospores suspended in tryptone-gelatin hydrolysate-lactose (TGhL) broth medium. Plates were then read daily on a spectrophotometer until positive controls reached maximum growth in order to determine growth curves for Bd. We tested the technique by screening skin bacteria from the Australian green-eyed tree frog Litoria serrata. Of bacteria tested, 31% showed some degree of Bd inhibition, while some may have promoted Bd growth, a previously unknown effect. Our cell-free supernatant challenge assay technique is an effective in vitro method for screening bacterial isolates for strong Bd-inhibitory activity. It contributes to the expanding field of bioaugmentation research, which could play a significant role in mitigating the effects of chytridiomycosis on amphibians around the world. © Inter-Research 2013. Source

Rusaini,Tadulako University | Rusaini,James Cook University | La Fauce K.A.,James Cook University | Elliman J.,James Cook University | And 2 more authors.

Nine endogenous Brevidensovirus-like elements (EBreVE) were identified in redclaw freshwater crayfish Cherax quadricarinatus from different sources suggesting that these elements are widespread in redclaw in northern Queensland, Australia. These endogenous virus-like elements shared nucleotide identities (70-100%) and amino acid similarities (34-100%) with infectious hypodermal and haematopoietic necrosis virus (IHHNV) scientifically classified as Penaeus stylirostris densovirus (PstDNV). They may not have originated from IHHNV genomes, but could be derived from another uncharacterised member of the genus Brevidensovirus that share nucleotide similarities with IHHNV. The most striking feature of EBreVEs was that in each case, the segment (portion) of viral sequences inserted into the host genomes was from the same region of the viral genome and most likely derived from non-structural protein regions of ancestral virus, but they cannot be assembled into one consensus sequence. The EBreVEs may be inserted into the redclaw genomes following chronic or persistent infection by a corresponding virus that may have occurred as multiple independent integration events years ago leading to the accumulation of several integrated elements in their genomes. Histological examination and polymerase chain reaction (PCR) suggested that these insertions may have a protective function to their host. © 2013 Elsevier B.V. Source

Bowater R.O.,Tropical and Aquatic Animal Health Laboratory | Forbes-Faulkner J.,Tropical and Aquatic Animal Health Laboratory | Anderson I.G.,Tropical and Aquatic Animal Health Laboratory | Condon K.,Tropical and Aquatic Animal Health Laboratory | And 7 more authors.
Journal of Fish Diseases

Ninety-three giant Queensland grouper, Epinephelus lanceolatus (Bloch), were found dead in Queensland, Australia, from 2007 to 2011. Most dead fish occurred in northern Queensland, with a peak of mortalities in Cairns in June 2008. In 2009, sick wild fish including giant sea catfish, Arius thalassinus (Rüppell), and javelin grunter, Pomadasys kaakan (Cuvier), also occurred in Cairns. In 2009 and 2010, two disease epizootics involving wild stingrays occurred at Sea World marine aquarium. Necropsy, histopathology, bacteriology and PCR determined that the cause of deaths of 12 giant Queensland grouper, three wild fish, six estuary rays, Dasyatis fluviorum (Ogilby), one mangrove whipray, Himantura granulata (Macleay), and one eastern shovelnose ray, Aptychotrema rostrata (Shaw), was Streptococcus agalactiae septicaemia. Biochemical testing of 34 S. agalactiae isolates from giant Queensland grouper, wild fish and stingrays showed all had identical biochemical profiles. The 16S rRNA gene sequences of isolates confirmed all isolates were S. agalactiae; genotyping of selected S. agalactiae isolates showed the isolates from giant Queensland grouper were serotype Ib, whereas isolates from wild fish and stingrays closely resembled serotype II. This is the first report of S. agalactiae from wild giant Queensland grouper and other wild tropical fish and stingray species in Queensland, Australia. © 2012 Blackwell Publishing Ltd and State of Queensland. Source

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