The impact of co-infections on fish: a review

International audienceAbstractCo-infections are very common in nature and occur when hosts are infected by two or more different pathogens either by simultaneous or secondary infections so that two or more infectious agents are active together in the same host. Co-infections have a fundamental effect and can alter the course and the severity of different fish diseases. However, co-infection effect has still received limited scrutiny in aquatic animals like fish and available data on this subject is still scarce. The susceptibility of fish to different pathogens could be changed during mixed infections causing the appearance of sudden fish outbreaks. In this review, we focus on the synergistic and antagonistic interactions occurring during co-infections by homologous or heterologous pathogens. We present a concise summary about the present knowledge regarding co-infections in fish. More research is needed to better understand the immune response of fish during mixed infections as these could have an important impact on the development of new strategies for disease control programs and vaccination in fish

Analysis of the distribution and evolution of the ATP-dependent DNA ligases of bacteria delineates a distinct phylogenetic group 'Lig E'

© 2016 John Wiley & Sons Ltd. Prior to the discovery of a minimal ATP-dependent DNA ligase in Haemophilus influenzae, bacteria were thought to only possess a NAD-dependent ligase, which was involved in sealing of Okazaki fragments. We now know that a diverse range of bacterial species possess up to six of these accessory bacterial ATP-dependent DNA ligases (b-ADLs), which vary in size and enzymatic domain associations. Here we compare the domain structure of different types of b-ADLs and investigate their distribution among the bacterial domain to describe possible evolutionary trajectories that gave rise to the sequence and structural diversity of these enzymes. Previous biochemical and genetic analyses have delineated three main classes of these enzymes: Lig B, Lig C and Lig D, which appear to have descended from a common ancestor within the bacterial domain. In the present study, we delineate a fourth group of b-ADLs, Lig E, which possesses a number of unique features at the primary and tertiary structural levels. The biochemical characteristics, domain structure and inferred extracellular location sets this group apart from the other b-ADLs. The results presented here indicate that the Lig E type ligases were horizontally transferred into bacteria in a separate event from other b-ADLs possibly from a bacteriophage. Some bacteria possess accessory ATP-dependent DNA ligases (ADLs) which vary in size and the composition of enzymatic domains and appear to have been horizontally acquired. Our analysis of the distribution and phylogeny of these bacterial ADLs suggests that types Lig B, Lig C and Lig D have descended from a common ancestor within the bacterial domain, while Lig E was transferred in a separate event, possibly from a bacteriophage

Whole-genome sequencing reveals clonal expansion of multiresistant Staphylococcus haemolyticus in European hospitals

© The Author 2014. Objectives: Staphylococcus haemolyticus is an emerging cause of nosocomial infections, primarily affecting immunocompromised patients. A comparative genomic analysis was performed on clinical S. haemolyticus isolates to investigate their genetic relationship and explore the coding sequences with respect to antimicrobial resistance determinants and putative hospital adaptation. Methods: Whole-genome sequencing was performed on 134 isolates of S. haemolyticus from geographically diverse origins (Belgium, 2; Germany, 10; Japan, 13; Norway, 54; Spain, 2; Switzerland, 43; UK, 9; USA, 1). Each genome was individually assembled. Protein coding sequences (CDSs) were predicted and homologous genes were categorized into three types: Type I, core genes, homologues present in all strains; Type II, unique core genes, homologues shared by only a subgroup of strains; and Type III, unique genes, strain-specific CDSs. The phylogenetic relationship between the isolates was built from variable sites in the form of single nucleotide polymorphisms (SNPs) in the core genome and used to construct a maximum likelihood phylogeny. Results: SNPs in the genome core regions divided the isolates into one major group of 126 isolates and one minor group of isolates with highly diverse genomes. The major group was further subdivided into seven clades (A-G), of which four (A-D) encompassed isolates only from Europe. Antimicrobial multiresistance was observed in 77.7% of the collection. High levels of homologous recombination were detected in genes involved in adherence, staphylococcal host adaptation and bacterial cell communication. Conclusions: The presence of several successful and highly resistant clones underlines the adaptive potential of this opportunistic pathogen

Supplementary Material for: Prediction, Microarray and Northern Blot Analyses Identify New Intergenic Small RNAs in <b><i>Aliivibrio salmonicida</i></b>

Bacterial small RNAs (sRNAs) are <i>trans</i>-encoded regulatory RNAs that typically bind mRNAs by short-sequence complementarities and change the expression of the corresponding proteins. Some of the well-characterized sRNAs serve critical steps in the regulation of important cellular processes, such as quorum sensing (Qrr), iron homeostasis (RyhB), oxidative stress (OxyS), and carbon metabolism (Spot 42). However, many sRNAs remain to be identified, and the functional roles of sRNAs are known for only a small fraction. For example, of the hundreds of candidate sRNAs from members of the bacterial family Vibrionaceae, the function is known for only 9. We have in this study significantly contributed to the discovery and verification of new sRNAs in a representative of Vibrionaceae, i.e. the <i>Aliivibrio salmonicida</i>, which causes severe disease in farmed Atlantic salmon and other fishes. A computational search for intergenic non-coding (nc) RNAs in the 4.6-Mb genome identified a total of 252 potential ncRNAs (including 233 putative sRNAs). Depending on the set threshold value for fluorescence signal in our microarray approach, we identified 50–80 putative ncRNAs, 12 of which were verified by Northern blot analysis. In total, we identified 9 new sRNAs

The alternative sigma factor RpoQ regulates colony morphology, biofilm formation and motility in the fish pathogen Aliivibrio salmonicida

Background: Quorum sensing (QS) is a cell-to cell communication system that bacteria use to synchronize activities as a group. LitR, the master regulator of QS in Aliivibrio salmonicida, was recently shown to regulate activities such as motility, rugosity and biofilm formation in a temperature dependent manner. LitR was also found to be a positive regulator of rpoQ. RpoQ is an alternative sigma factor belonging to the sigma −70 family. Alternative sigma factors direct gene transcription in response to environmental signals. In this work we have studied the role of RpoQ in biofilm formation, colony morphology and motility of A. salmonicida LFI1238. Results: The rpoQ gene in A. salmonicida LFI1238 was deleted using allelic exchange. We found that RpoQ is a strong repressor of rugose colony morphology and biofilm formation, and that it controls motility of the bacteria. We also show that overexpression of rpoQ in a ΔlitR mutant of A. salmonicida disrupts the biofilm produced by the ΔlitR mutant and decreases its motility, whereas rpoQ overexpression in the wild-type completely eliminates the motility. Conclusion: The present work demonstrates that the RpoQ sigma factor is a novel regulatory component involved in modulating motility, colony morphology and biofilm formation in the fish pathogen A. salmonicida. The findings also confirm that RpoQ functions downstream of the QS master regulator LitR. However further studies are needed to elucidate how LitR and RpoQ work together in controlling phenotypes related to QS in A. salmonicida