From the Microbiome to the Electrome: Implications for the Microbiota-Gut-Brain Axis.

The gut microbiome plays a fundamental role in metabolism, as well as the immune and nervous systems. Microbial imbalance (dysbiosis) can contribute to subsequent physical and mental pathologies. As such, interest has been growing in the microbiota-gut-brain brain axis and the bioelectrical communication that could exist between bacterial and nervous cells. The aim of this study was to investigate the bioelectrical profile (electrome) of two bacterial species characteristic of the gut microbiome: a Proteobacteria Gram-negative bacillus Escherichia coli (E. coli), and a Firmicutes Gram-positive coccus Enterococcus faecalis (E. faecalis). We analyzed both bacterial strains to (i) validate the fluorescent probe bis-(1,3-dibutylbarbituric acid) trimethine oxonol, DiBAC4(3), as a reliable reporter of the changes in membrane potential (Vmem) for both bacteria; (ii) assess the evolution of the bioelectric profile throughout the growth of both strains; (iii) investigate the effects of two neural-type stimuli on Vmem changes: the excitatory neurotransmitter glutamate (Glu) and the inhibitory neurotransmitter γ-aminobutyric acid (GABA); (iv) examine the impact of the bioelectrical changes induced by neurotransmitters on bacterial growth, viability, and cultivability using absorbance, live/dead fluorescent probes, and viable counts, respectively. Our findings reveal distinct bioelectrical profiles characteristic of each bacterial species and growth phase. Importantly, neural-type stimuli induce Vmem changes without affecting bacterial growth, viability, or cultivability, suggesting a specific bioelectrical response in bacterial cells to neurotransmitter cues. These results contribute to understanding the bacterial response to external stimuli, with potential implications for modulating bacterial bioelectricity as a novel therapeutic target.

Bioelectrical State of Bacteria Is Linked to Growth Dynamics and Response to Neurotransmitters: Perspectives for the Investigation of the Microbiota-Brain Axis.

Inter-cellular communication is mediated by a sum of biochemical, biophysical, and bioelectrical signals. This might occur not only between cells belonging to the same tissue and/or animal species but also between cells that are, from an evolutionary point of view, far away. The possibility that bioelectrical communication takes place between bacteria and nerve cells has opened exciting perspectives in the study of the gut microbiota-brain axis. The aim of this paper is (i) to establish a reliable method for the assessment of the bioelectrical state of two bacterial strains: Bacillus subtilis (B. subtilis) and Limosilactobacillus reuteri (L. reuteri); (ii) to monitor the bacterial bioelectrical profile throughout its growth dynamics; and (iii) to evaluate the effects of two neurotransmitters (glutamate and γ-aminobutyric acid-GABA) on the bioelectrical signature of bacteria. Our results show that membrane potential (Vmem) and the proliferative capacity of the population are functionally linked in B. subtilis in each phase of the cell cycle. Remarkably, we demonstrate that bacteria respond to neural signals by changing Vmem properties. Finally, we show that Vmem changes in response to neural stimuli are present also in a microbiota-related strain L. reuteri. Our proof-of-principle data reveal a new methodological approach for the better understanding of the relation between bacteria and the brain, with a special focus on gut microbiota. Likewise, this approach will open exciting perspectives in the study of the inter-cellular mechanisms which regulate the bi-directional communication between bacteria and neurons and, ultimately, for designing gut microbiota-brain axis-targeted treatments for neuropsychiatric diseases.

Influence of malnutrition upon all-cause mortality among children in Swaziland.

OBJECTIVE: To analyze the effect of the type of malnutrition, sex, age and the presence of edema upon all-cause mortality in children under 5 years of age. MATERIAL AND METHODS: A cross-sectional study was conducted during 2010 and 2011 in Swaziland. Sex, age, weight and height were taken to classify nutritional status according to the 2006 WHO growth standards: stunting (low height for age), wasting (low weight for height or low body mass index for age) and underweight (low weight for age). The sample (309 boys and 244 girls under 5 years of age) was analyzed by sex and age groups (under and equal/over 12 months). The association between variables was evaluated using the χ2 test. Cox regression analysis (HR, 95% CI) was used to assess the likelihood of mortality. RESULTS: The mortality risk in malnourished children under one year of age was lower among females and increased in the presence of severe edema. Wasting combined with underweight increased the mortality risk in children under 12 months of age 5-fold, versus 11-fold in older children. The combination of stunting, wasting and underweight was closely associated to mortality. Stunting alone (not combined with wasting) did not significantly increase the mortality risk. CONCLUSIONS: Sex, severe edema and wasting are predictors of mortality in malnourished children. Regardless of these factors, children with deficiencies referred to weight for height and weight for age present a greater mortality risk in comparison with children who present stunting only.