Identification and virulence of Aeromonas dhakensis, Pseudomonas mosselii and Microbacterium paraoxydans isolated from Nile tilapia, Oreochromis niloticus, cultivated in Mexico.

AIMS: To identify bacterial pathogens of diseased NiIe tilapia Oreochromis niloticus and determine their virulence. METHODS AND RESULTS: Sixteen bacterial isolates were recovered from diseased Nile tilapias (O. niloticus) reared in floating cages in Adolfo Lopez Mateos (ALM), Sanalona and Dique IV dams in Sinaloa, Mexico, from February to May 2009. The bacterial isolates were identified by phenotypic and molecular (rep-PCR and 16S rRNA sequencing) methods and were mostly isolated from the kidneys and the brain of tilapias. Bacterial cells and extracellular products (ECPs) of strains were characterized and used in experimental infections with sole Solea vulgaris and Mozambican tilapia Oreochromis mossambicus. The fish challenged with Aeromonas dhakensis sp. nov. comb nov, Pseudomonas mosselii and Microbacterium paraoxydans (3·1 × 10(6)  CFU g(-) 1) exhibited mortality between 40 and 100% starting at 6 h postinoculation. The ECPs displayed gelatinase, haemolytic and cytotoxic activity, causing the total destruction of the HeLa cell lines. CONCLUSIONS: Aeromonas dhakensis and Ps. mosselii were virulent to O. mossambicus, whereas Mic. paraoxydans displayed virulence to S. vulgaris. SIGNIFICANCE AND IMPACT OF THE STUDY: This the first time that Aeromonas dhakensis and Ps. mosselii are reported as pathogens to tilapia and Mic. paraoxydans was isolated from fish; then, these fish pathogens could be a threat to farmed Nile tilapia in Mexico.

Serological and molecular heterogeneity among Yersinia ruckeri strains isolated from farmed Atlantic salmon Salmo salar in Chile.

We investigated 11 strains of Yersinia ruckeri, the causative agent of enteric redmouth disease (ERM), that had been isolated from Atlantic salmon Salmo salar L. farmed in Chile and previously vaccinated against ERM. Phylogenetic analysis of the 16S rRNA gene sequences confirmed the identification of the salmon isolates as Y. ruckeri. A comparative analysis of the biochemical characteristics was made by means of traditional and commercial miniaturised methods. All studied isolates were motile and Tween 80 positive, and were identified as biotype 1. In addition, drug susceptibility tests determined high sensitivity to sulphamethoxazole/trimethroprim, oxytetracycline, ampicillin and enrofloxacin in all isolates. Serological assays showed the presence of O1a, O1b and O2b serotypes, with a predominance of the O1b serotype in 9 strains. Analysis of the lipopolysaccharide profiles and the correspondent immunoblot confirmed these results. Sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE) of the outer membrane proteins revealed that all Chilean strains had profiles with a molecular weight range between 34 and 55 kDa, with 3 distinct groups based on differences in the major bands. Genotyping analyses by enterobacterial repetitive intergenic consensus (ERIC-) and repetitive extragenic palindromic (REP-)PCR techniques clearly indicated intraspecific genetic diversity among Chilean Y. ruckeri strains.

Genetic characterization of Streptococcus phocae strains isolated from Atlantic salmon, Salmo salar L., in Chile.

Streptococcus phocae is a beta-haemolytic bacterium frequently involved in disease outbreaks in seals causing pneumonia or respiratory infection. Since 1999, this pathogen has been isolated from diseased Atlantic salmon, Salmo salar, causing serious economic losses in the salmon industry in Chile. In this study, we used different molecular typing methods, such as pulsed-field gel electrophoresis (PFGE), randomly amplified polymorphic DNA (RAPD), enterobacterial repetitive intergenic consensus sequence PCR (ERIC-PCR), repetitive extragenic palindromic PCR (REP-PCR) and restriction of 16S-23S rDNA intergenic spacer regions to evaluate the genetic diversity in S. phocae. Thirty-four strains isolated in different years were analysed. The S. phocae type strain ATCC 51973(T) was included for comparative purposes. The results demonstrated genetic homogeneity within the S. phocae strains isolated in Chile over several years, suggesting the existence of clonal relationships among S. phocae isolated from Atlantic salmon. The type strain ATCC 51973(T) presented a different genetic pattern with the PFGE, RAPD, ERIC-PCR and REP-PCR methods. However, the fingerprint patterns of two seal isolates were distinct from those of the type strain.

Global market: shellfish imports as a source of reemerging food-borne hepatitis A virus infections in Spain.

A total of 16 mollusk imports from South America to Spain, including clam and scallop species, were analyzed for hepatitis A virus (HAV), due to the great concern about this type of food after an important hepatitis A outbreak in eastern Spain in September 1999. In addition, clams from the stock that had caused the outbreak were also tested. Of the 17 stocks, four were positive for the presence of HAV RNA as demonstrated by RT-PCR and Southern hybridization. Contradictory analyses confirmed the results of the primary tests in all cases. The findings obtained in this work strongly support the role of mollusk imports from endemic areas of HAV as an important vehicle of hepatitis A, and demonstrate the imperative need for sanitary control measures to prevent future outbreaks of this disease.