Genomic characterization of Aeromonas spp. isolates from striped catfish with motile Aeromonas septicemia and human bloodstream infections in Vietnam.

Aeromonas spp. are commonly found in the aquatic environment and have been responsible for motile Aeromonas septicemia (MAS) in striped catfish, resulting in significant economic loss. These organisms also cause a range of opportunistic infections in humans with compromised immune systems. Here, we conducted a genomic investigation of 87 Aeromonas isolates derived from diseased catfish, healthy catfish and environmental water in catfish farms affected by MAS outbreaks in eight provinces in Mekong Delta (years: 2012-2022), together with 25 isolates from humans with bloodstream infections (years: 2010-2020). Genomics-based typing method precisely delineated Aeromonas species while traditional methods such as aerA PCR and MALDI-TOF were unable identify A. dhakensis. A. dhakensis was found to be more prevalent than A. hydrophila in both diseased catfish and human infections. A. dhakensis sequence type (ST) 656 followed by A. hydrophila ST251 were the predominant virulent species-lineages in diseased catfish (43.7 and 20.7 %, respectively), while diverse STs were found in humans with bloodstream infections. There was evidence of widespread transmission of ST656 and ST251 on striped catfish in the Mekong Delta region. ST656 and ST251 isolates carried a significantly higher number of acquired antimicrobial resistance (AMR) genes and virulence factors in comparison to other STs. They, however, exhibited several distinctions in key virulence factors (i.e. lack of type IV pili and enterotoxin ast in A. dhakensis), AMR genes (i.e. presence of imiH carbapenemase in A. dhakensis), and accessory gene content. To uncover potential conserved proteins of Aeromonas spp. for vaccine development, pangenome analysis has unveiled 2202 core genes between ST656 and ST251, of which 78 proteins were in either outer membrane or extracellular proteins. Our study represents one of the first genomic investigations of the species distribution, genetic landscape, and epidemiology of Aeromonas in diseased catfish and human infections in Vietnam. The emergence of antimicrobial resistant and virulent A. dhakensis strains underscores the needs of enhanced genomic surveillance and strengthening vaccine research and development in preventing Aeromonas diseases in catfish and humans, and the search for potential vaccine candidates could focus on Aeromonas core genes encoded for membrane and secreted proteins.

Effects of Glycogen on Ceramide Production in Cultured Human Keratinocytes via Acid Sphingomyelinase Activation.

Glycogen is a highly branched storage polysaccharide found mainly in the liver and the muscles. Glycogen is also present in the skin, but its functional role is poorly understood. Recently, it has been reported that glycogen plays an important role in intracellular signal transduction. In the epidermis of the skin, keratinocytes are the predominant cells that produce ceramide. Ceramides are lipids composed of sphingosine, and prevent water loss, as well as protecting the skin against environmental stressors. In this study, we investigated the effects of glycogen on ceramide production in cultured keratinocytes. Thin-layer chromatography revealed that incubation of keratinocytes with 2 % glycogen enhanced the cellular amount of ceramide NS (ceramide 2) by 3.4-fold compared to the control. We also found that glycogen regulated the mRNA expression levels of signaling molecules of the sphingomyelin-ceramide pathway by quantitative real-time PCR. The activity of sphingomyelinase was also significantly enhanced by 2.5-fold in cultures with 1 % glycogen compared to the control. Moreover, glycogen increased the ATP production by 1.5-fold compared to the control, while glucose did not affect the production. Western blotting showed that phosphorylation of Akt, a cellular signaling molecule, was inhibited in the presence of glycogen in cultured keratinocytes. This study shows that glycogen upregulates the ceramide production pathway from sphingomyelin in epidermal keratinocytes, and provides new insights into the role of glycogen in cellular signal transduction.