Identification of genes in a KG- phenotype of Lactococcus garvieae, a fish pathogenic bacterium, whose proteins react with antiKG- rabbit serum

Lactococcosis a Re-Emerging Disease in Aquaculture: Disease Significant and Phytotherapy

Lactococcosis, particularly that caused by Lactococcus garvieae, is a major re-emerging bacterial disease seriously affecting the sustainability of aquaculture industry. Medicinal herbs and plants do not have very much in vitro antagonism and in vivo disease resistance towards lactococcosis agents in aquaculture. Most in vitro studies with herbal extractives were performed against L. garvieae with no strong antibacterial activity, but essential oils, especially those that contain thymol or carvacrol, are more effective. The differences exhibited by the bacteriostatic and bactericidal functions for a specific extractive in different studies could be due to different bacterial strains or parts of chemotypes of the same plant. Despite essential oils being shown to have the best anti-L. garvieae activity in in vitro assays, the in vivo bioassays required further study. The extracts tested under in vivo conditions presented moderate efficacy, causing a decrease in mortality in infected animals, probably because they improved immune parameters before challenging tests. This review addressed the efficacy of medicinal herbs to lactococcosis and discussed the presented gaps.

Lactococcus garvieae: an emerging bacterial pathogen of fish

Lactococcus garvieae is the causative agent of lactococcosis, a hyperacute, haemorrhagic septicaemia of fish. This bacterium is also considered an emerging zoonotic pathogen, as reports of human infection are increasing. Significant economic loss in aquaculture is suffered as a result of lactococcosis, as numerous freshwater and marine species of commercial interest are affected. Development of antibiotic resistance in L. garvieae to several chemotherapeutic agents complicates and restricts treatment options. Effective, sustainable treatment and prevention options are thus needed, but progress is impeded by the lack of knowledge concerning several aspects of the disease and the pathogen. This review aims to present the latest research on L. garvieae, with specific focus on pathogenesis, virulence factors, risks associated with chemotherapeutic administration and possible control options.

Analysis of the genome content of Lactococcus garvieae by genomic interspecies microarray hybridization

Background

Lactococcus garvieae is a bacterial pathogen that affects different animal species in addition to humans. Despite the widespread distribution and emerging clinical significance of L. garvieae in both veterinary and human medicine, there is almost a complete lack of knowledge about the genetic content of this microorganism. In the present study, the genomic content of L. garvieae CECT 4531 was analysed using bioinformatics tools and microarray-based comparative genomic hybridization (CGH) experiments. Lactococcus lactis subsp. lactis IL1403 and Streptococcus pneumoniae TIGR4 were used as reference microorganisms.

Results

The combination and integration of in silico analyses and in vitro CGH experiments, performed in comparison with the reference microorganisms, allowed establishment of an inter-species hybridization framework with a detection threshold based on a sequence similarity of ≥ 70%. With this threshold value, 267 genes were identified as having an analogue in L. garvieae, most of which (n = 258) have been documented for the first time in this pathogen. Most of the genes are related to ribosomal, sugar metabolism or energy conversion systems. Some of the identified genes, such as als and mycA, could be involved in the pathogenesis of L. garvieae infections.

Conclusions

In this study, we identified 267 genes that were potentially present in L. garvieae CECT 4531. Some of the identified genes could be involved in the pathogenesis of L. garvieae infections. These results provide the first insight into the genome content of L. garvieae.

Immunoproteomic analysis of capsulate and non-capsulate strains of Lactococcus garvieae

A comparative immunoproteomic study was carried out to investigate the immunogenicity of capsulate (KG9408) and non-capsulate (NSS9310) strains of Lactococcus garvieae. Immunoblot assays, following two-dimensional gel electrophoresis (2-DE) for L. garvieae strains, revealed a significant difference between anti-capsulate and anti-non-capsulate rabbit sera with respect to the number and antigenicity of antigenic spots. Anti-capsulate and anti-non-capsulate rabbit sera reacted with an average of 72 and 127 antigenic spots, respectively. The strong reaction of anti-non-capsulate sera with elongation factor (EF)-G and -Tu, and GMP synthase, of the L. garvieae strains identifies these as specific major antigens. This study clearly demonstrates the differences in 2-DE immunoblot profiles between the capsulate and non-capsulate strains of L. garvieae. These differences may be the reason for variations in immunogenicity between capsulate and non-capsulate strains. Glyceraldehyde-3-phosphate dehydrogenase, phosphoglycerate kinase, arginine deaminase and ornithine carbamoyltransferase were identified from the 2-DE immunoblot profiles of both strains. Therefore, these common antigens are potential markers for the development of vaccines against L. garvieae, irrespective of strain. Immunoproteomics, a powerful tool for studying antigens at the proteomic level, allowed a comparative investigation of the immunogenicity of capsulate and non-capsulate strains of L. garvieae for vaccine development.

Conserved genes in a path from commensalism to pathogenicity: comparative phylogenetic profiles of Staphylococcus epidermidis RP62A and ATCC12228

Background

Staphylococcus epidermidis, long regarded as an innocuous commensal bacterium of the human skin, is the most frequent cause of nosocomial infections associated with implanted medical devices. This conditional pathogen provides a model of choice to study genome landmarks correlated with the transition between commensalism and pathogenicity. Traditional investigations stress differences in gene content. We focused on conserved genes that have accumulated small mutation differences during the transition.

Results

A comparison of strain ATCC12228, a non-biofilm forming, non-infection associated strain and strain RP62A, a methicillin-resistant biofilm clinical isolate, revealed consistent variation, mostly single-nucleotide polymorphisms (SNPs), in orthologous genes in addition to the previously investigated global changes in gene clusters. This polymorphism, scattered throughout the genome, may reveal genes that contribute to adaptation of the bacteria to different environmental stimuli, allowing them to shift from commensalism to pathogenicity. SNPs were detected in 931 pairs of orthologs with identical gene length, accounting for approximately 45% of the total pairs of orthologs. Assuming that non-synonymous mutations would mark recent evolution, and hence be associated to the onset of the pathogenic process, analysis of ratios of non-synonymous SNPs vs synonymous SNPs suggested hypotheses about possible pathogenicity determinants. The N/S ratios for virulence factors and surface proteins differed significantly from that of average SNPs. Of those gene pairs, 40 showed a disproportionate distribution of dN vs dS. Among those, the presence of the gene encoding methionine sulfoxide reductase suggested a possible involvement of reactive oxygen species. This led us to uncover that the infection associated strain was significantly more resistant to hydrogen peroxide and paraquat than the environmental strain. Some 16 genes of the list were of unknown function. We could suggest however that they were likely to belong to surface proteins or considered in priority as important for pathogenicity.

Conclusion

Our study proposed a novel approach to identify genes involved in pathogenic processes and provided some insight about the molecular mechanisms leading a commensal inhabitant to become an invasive pathogen.

Construction of transposition insertion libraries and specific gene inactivation in the pathogen Lactococcus garvieae

This paper reports the development of genetic tools in Lactococcus garvieae, an important Gram-positive bacterial pathogen affecting both fish and mammals. The vector pGKV210, a broad host range vector, was introduced by electroporation into L. garvieae UNIUD074. The maximal frequency obtained was 3.2 x 10(5) transformants/mug of DNA. Moreover, this effect is highly reproducible and appears to be constant, since all L. garvieae strains tested were transformed. Once the optimal transformation procedure was established, it was used to generate isogenic and transposition mutants. Insertional mutagenesis of the L. garvieae SA9H10L gene, similar to a Streptococcus pyogenes gene encoding the M protein (emm64), was carried out using the conditional replication plasmid pORI19. Transposition mutagenesis using the streptococcal temperature-sensitive suicide vector pTV408 to deliver Tn917 into the chromosome of L. garvieae was also achieved at a frequency of ca. 10(-4). Transposon flanking DNA sequences were obtained by plasmid rescue in Escherichia coli and their sequencing analysis demonstrated that the transposon was inserted at different chromosomal loci. Tn917 also made it possible to select a mutant in the operon involved in mannitol fermentation in this microorganism. The results obtained in the present study lay the foundation for future research on the virulence mechanisms of L. garvieae.