Global transcriptome analysis of Lactococcus garvieae strains in response to temperature

Lactococcus garvieae is an important fish and an opportunistic human pathogen. The genomic sequences of several L. garvieae strains have been recently published, opening the possibility of global studies on the biology of this pathogen. In this study, a whole genome DNA microarray of two strains of L. garvieae was designed and validated. This DNA microarray was used to investigate the effects of growth temperature (18°C and 37°C) on the transcriptome of two clinical strains of L. garvieae that were isolated from fish (Lg8831) and from a human case of septicemia (Lg21881). The transcriptome profiles evidenced a strain-specific response to temperature, which was more evident at 18°C. Among the most significant findings, Lg8831 was found to up-regulate at 18°C several genes encoding different cold-shock and cold-induced proteins involved in an efficient adaptive response of this strain to low-temperature conditions. Another relevant result was the description, for the first time, of respiratory metabolism in L. garvieae, whose gene expression regulation was temperature-dependent in Lg21881. This study provides new insights about how environmental factors such as temperature can affect L. garvieae gene expression. These data could improve our understanding of the regulatory networks and adaptive biology of this important pathogen.

Garvicin A, a novel class IId bacteriocin from Lactococcus garvieae that inhibits septum formation in L. garvieae strains

Lactococcus garvieae 21881, isolated in a human clinical case, produces a novel class IId bacteriocin, garvicin A (GarA), which is specifically active against other L. garvieae strains, including fish- and bovine-pathogenic isolates. Purification from active supernatants, sequence analyses, and plasmid-curing experiments identified pGL5, one of the five plasmids found in L. garvieae [M. Aguado-Urda et al., PLoS One 7(6):e40119, 2012], as the coding plasmid for the structural gene of GarA (lgnA), its putative immunity protein (lgnI), and the ABC transporter and its accessory protein (lgnC and lgnD). Interestingly, pGL5-cured strains were still resistant to GarA. Other putative bacteriocins encoded by the remaining plasmids were not detected during purification, pointing to GarA as the main inhibitor secreted by L. garvieae 21881. Mode-of-action studies revealed a potent bactericidal activity of GarA. Moreover, transmission microscopy showed that GarA seems to act by inhibiting septum formation in L. garvieae cells. This potent and species-specific inhibition by GarA holds promise for applications in the prevention or treatment of infections caused by pathogenic strains of L. garvieae in both veterinary and clinical settings.

Characterization of some bacterial strains isolated from animal clinical materials and identified as Corynebacterium xerosis by molecular biological techniques

Eighteen Corynebacterium xerosis strains isolated from different animal clinical specimens were subjected to phenotypic and molecular genetic studies. On the basis of the results of the biochemical characterization, the strains were tentatively identified as C. xerosis. Phylogenetic analysis based on comparative analysis of the sequences of 16S rRNA and rpoB genes revealed that the 18 strains were highly related to C. xerosis, C. amycolatum, C. freneyi, and C. hansenii. There was a good concordance between 16S rRNA and partial rpoB gene sequencing results, although partial rpoB gene sequencing allowed better differentiation of C. xerosis. Alternatively, C. xerosis was also differentiated from C. freneyi and C. amycolatum by restriction fragment length polymorphism analysis of the 16S-23S rRNA gene intergenic spacer region. Phenotypic characterization indicated that besides acid production from D-turanose and 5-ketogluconate, 90% of the strains were able to reduce nitrate. The absence of the fatty acids C(14:0), C(15:0), C(16:1)omega 7c, and C(17:1)omega 8c can also facilitate the differentiation of C. xerosis from closely related species. The results of the present investigation demonstrated that for reliable identification of C. xerosis strains from clinical samples, a combination of phenotypic and molecular-biology-based identification techniques is necessary.