Development and characterization of a bacteriophage cocktail with high lytic efficacy against field-isolated Salmonella enterica

Salmonella spp. is a prevalent pathogen that causes great public health concern worldwide. Bacteriophage-based cocktails have arisen as an alternative to antibiotics to inhibit the growth of Salmonella. However, the bactericidal effect of bacteriophage cocktails in vivo largely differs from their observed effect in vitro. This is partly because in vitro developments of cocktails do not always consider the bacterial diversity nor the environmental conditions where bacteriophages will have to replicate. Here, we isolated and sequenced 47 bacteriophages that showed variable degrees of lytic activity against 258 Salmonella isolates from a commercial broiler company in Brazil. Three of these bacteriophages were characterized and selected to assemble a cocktail. In vitro quantitative assays determined the cocktail to be highly effective against multiple serovars of Salmonella, including Minnesota and Heidelberg. Remarkably, the in vitro lytic activity of the cocktail was retained or improved in conditions that more closely resembled the chicken gut, such as anaerobiosis, 42°C, and Salmonella mono-strain biofilms. Analysis of bacterial cross-resistance between the 3 bacteriophages composing the cocktail revealed limited or no generation of cross-resistance. Our results highlight the relevance of an optimized flux of work to develop bacteriophage cocktails against Salmonella with high lytic efficacy and strong potential to be applied in vivo in commercial broiler farms.

Crystal structure of the 6-phosphogluconate dehydrogenase from Gluconobacter oxydans reveals tetrameric 6PGDHs as the crucial intermediate in the evolution of structure and cofactor preference in the 6PGDH family

Background: The enzyme 6-phosphogluconate dehydrogenase (6PGDH) is the central enzyme of the oxidative pentose phosphate pathway. Members of the 6PGDH family belong to different classes: either homodimeric enzymes assembled from long-chain subunits or homotetrameric ones assembled from short-chain subunits. Dimeric 6PGDHs bear an internal duplication absent in tetrameric 6PGDHs and distant homologues of the β-hydroxyacid dehydrogenase (βHADH) superfamily. Methods: We use X-ray crystallography to determine the structure of the apo form of the 6PGDH from Gluconobacter oxydans (Go6PGDH). We carried out a structural and phylogenetic analysis of short and long-chain 6PGDHs. We put forward an evolutionary hypothesis explaining the differences seen in oligomeric state vs. dinucleotide preference of the 6PGDH family. We determined the cofactor preference of Go6PGDH at different 6-phosphogluconate concentrations, characterizing the wild-type enzyme and three-point mutants of residues in the cofactor binding site of Go6PGDH. Results: The structural comparison suggests that the 6PG binding site initially evolved by exchanging C-terminal α-helices between subunits. An internal duplication event changed the quaternary structure of the enzyme from a tetrameric to a dimeric arrangement. The phylogenetic analysis suggests that 6PGDHs have spread from Bacteria to Archaea and Eukarya on multiple occasions by lateral gene transfer. Sequence motifs consistent with NAD+- and NADP+-specificity are found in the β2-α2 loop of dimeric and tetrameric 6PGDHs. Site-directed mutagenesis of Go6PGDH inspired by this analysis fully reverses dinucleotide preference. One of the mutants we engineered has the highest efficiency and specificity for NAD+ so far described for a 6PGDH. Conclusions: The family 6PGDH comprises dimeric and tetrameric members whose active sites are conformed by a C-terminal α-helix contributed from adjacent subunits. Dimeric 6PGDHs have evolved from the duplication-fusion of the tetrameric C-terminal domain before independent transitions of cofactor specificity. Changes in the conserved β2-α2 loop are crucial to modulate the cofactor specificity in Go6PGDH.

Inflammatory profiles in Chilean Mapuche and non-Mapuche women with gallstones at risk of developing gallbladder cancer

Chile has high incidence rates of gallbladder cancer globally, particularly among Amerindian women, who also have a high prevalence of gallstones. We examined differences in inflammatory biomarkers between Mapuche and non-Mapuche women from the Chile Biliary Longitudinal Study, a cohort of women with ultrasound-detected gallstones. We randomly selected 200 Mapuche women frequency matched to non-Mapuche women on age and statin use Inflammatory biomarkers were analyzed using a multiplex assay and linear regression to assess associations of a priori markers (CCL20, CXCL10, IL-6, and IL-8) with ethnicity. Novel biomarkers were analyzed using exploratory factor analysis (EFA) and sufficient dimension reduction (SDR) to identify correlated marker groups, followed by linear regression to examine their association with ethnicity. The mean values of IL-8 were higher in Mapuche than non-Mapuche women (P = 0.04), while CCL20, CXCL10, and IL-6 did not differ significantly by ethnicity. EFA revealed two marker groups associated with ethnicity (P = 0.03 and P < 0.001). SDR analysis confirmed correlation between the biomarkers and ethnicity. We found higher IL-8 levels among Mapuche than non-Mapuche women. Novel inflammatory biomarkers were correlated with ethnicity and should be studied further for their role in gallbladder disease. These findings may elucidate underlying ethnic disparities in gallstones and carcinogenesis among Amerindians.