Aims: This study describes a novel species within the genus Edwardsiella based on phenotypic and genetic characterization of fish pathogenic Edwardsiella isolates previously identified as E. tarda. Methods and Results: Phenotypic characterization, DNA-DNA hybridization and phylogenetic analysis of representative Edwardsiella isolates from fish previously identified as E. tarda were conducted and compared with E. tarda type strain (ATCC 15947 T ). Phenotypically, strains from fish grow with pinpoint colonies producing slight b-haemolysis under the colony. In contrast to the E. tarda type strain, fish strains did not grow at 42°C or degrade b-methyl-D-glucoside (with the exception of NCIMB 2034), citric acid and L-proline. With the exception of strain ETK01, all fish strains were highly pathogenic to zebra fish, while ATCC 15947 T and NCIMB 2034 were nonpathogenic. DNA-DNA hybridization (DDH) levels between representative fish isolates and the E. tarda type strain ranged from 15 to 43Á6%, while NCIMB 2034 hybridised with the type strain at the level of 63Á2%. DDH values between the various fish isolates ranged from 68Á2 to 93Á9% defining a new and separate DNA hybridization group differing from the E. tarda type strain consistent with the findings of phylogenetic analysis, in which the fish isolates comprised a separate clade. Conclusions: Phenotypical and genetic characterizations demonstrated that Edwardsiella isolates from fish described in this study do not belong to the species E. tarda or any of the previously established taxa within the genus Edwardsiella. The fish related strains studied here (excluding NCIMB 2034) represent, therefore, a novel species within the genus Edwardsiella for which we propose the name Edwardsiella piscicida sp. nov, with strain ET883 T (NCIMB 14824 T = CCUG 62929) as the type strain. Significance and Impact of the study: The current finding will improve the diagnosis, understanding of the epidemiology and in establishment of effective control measures against this serious fish pathogen.

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BackgroundMannheimia haemolytica has been recognized as the principal cause of pneumonic pasteurellosis in sheep and goats. It is one of the important diseases of small ruminants in Ethiopia. While annual vaccination using a monovalent vaccine (inactivated Pasteurella multocida biotype A) is common, respiratory diseases are still reported in various parts of Ethiopia. This suggests the need for further investigation into the species and strains responsible for the disease, which is vital information for development of a multivalent vaccine. The objective of the current study was to isolate M. heamolytica associated with pneumonic cases of sheep in selected areas of Central Ethiopia, determine its role and the strains/genotypes of the bacterium circulating in the study area.ResultsBacteriological analysis of nasal swab samples collected from a total of 76 pneumonic cases of sheep showed that M. haemolytica was isolated from 26 of them while B.trehalosi from two cases. Further molecular analyses of the isolates using M. haemolytica species-specific and M.haemolytica serotype-1 antigen specific PCR assays revealed, 26 of the isolates were identified as M. haemolytica of which 21 of them were M. haemolytica serotype-1. Both M. haemolytica and B.trehalosi isolates were not detected in a PCR assay targeting capsular biosynthesis gene (capA) of P.multocida despite the non-specific products observed in M. haemolytica isolates. Phylogenetic analysis of M. haemolytica isolates included in this study in comparison with the reference strains with respect to PHSSA and Rpt2 genes revealed that the Ethiopian M. haemolytica isolates constituted three distinct genotypes consistent with site of origin.ConclusionThe study indicated that M.haemolytica is commonly associated with cases of pneumonia in sheep in the study areas of central Ethiopia although the remaining other pathogens responsible for majority of the cases are yet to be determined. Molecular characterization revealed the existence of three genotypes of M. haemolytica circulating in the study areas consistent to the site of isolation. The findings suggest further extensive work to determine all pathogens associated with sheep pneumonia and the strain distribution of M. heamolytica to understand its molecular epidemiology at national level and design cost effective prevention and control methods.