A flow cytometry method for safe detection of bacterial viability.

Flow cytometry is a relevant tool to meet the requirements of academic and industrial research projects aimed at estimating the features of a bacterial population (e.g., quantity, viability, activity). One of the remaining challenges is now the safe assessment of bacterial viability while minimizing the risks inherent to existing protocols. In our core facility at the Paris-Saclay University, we have addressed this issue with two objectives: measuring bacterial viability in biological samples and preventing bacterial contamination and chemical exposure of the staff and cytometers used on the platform. Here, we report the development of a protocol achieving these two objectives, including a viability labeling step before bacteria fixation, which removes the risk of biological exposure, and the decrease of the use of reagents such as propidium iodide (PI), which are dangerous for health (CMR: carcinogenic, mutagenic, and reprotoxic). For this purpose, we looked for a non-CMR viability dye that can irreversibly label dead bacteria before fixation procedures and maintain intense fluorescence after further staining. We decided to test on the bacteria, eFluor Fixable Viability dyes, which are usually used on eukaryotic cells. Since the bacteria had size and granularity characteristics very similar to those associated with flow cytometry background signals, a step of bacterial DNA labeling with SYTO or DRAQ5 was necessarily added to differentiate them from the background. Three marker combinations (viability-DNA) were tested on LSR Fortessa and validated on pure bacterial populations (Gram+ , Gram- ) and polybacterial cultures. Any of the three methods can be used and adapted to the needs of each project and allow users to adapt the combination according to the configuration of their cytometer. Having been tested on six bacterial populations, validated on two cytometers, and repeated at least two times in each evaluated condition, we consider this method reliable in the context of these conditions. The reliability of the results obtained in flow cytometry was successfully validated by applying this protocol to confocal microscopy, permeabilization, and also to follow cultures over time. This flow cytometry protocol for measuring bacterial viability under safer conditions also opens the prospect of its use for further bacterial characterization.

Intestinal microbiota contributes to individual susceptibility to alcoholic liver disease.

OBJECTIVE: There is substantial inter-individual diversity in the susceptibility of alcoholics to liver injury. Alterations of intestinal microbiota (IM) have been reported in alcoholic liver disease (ALD), but the extent to which they are merely a consequence or a cause is unknown. We aimed to demonstrate that a specific dysbiosis contributes to the development of alcoholic hepatitis (AH). DESIGN: We humanised germ-free and conventional mice using human IM transplant from alcoholic patients with or without AH. The consequences on alcohol-fed recipient mice were studied. RESULTS: A specific dysbiosis was associated with ALD severity in patients. Mice harbouring the IM from a patient with severe AH (sAH) developed more severe liver inflammation with an increased number of liver T lymphocyte subsets and Natural Killer T (NKT) lymphocytes, higher liver necrosis, greater intestinal permeability and higher translocation of bacteria than mice harbouring the IM from an alcoholic patient without AH (noAH). Similarly, CD45+ lymphocyte subsets were increased in visceral adipose tissue, and CD4(+)T and NKT lymphocytes in mesenteric lymph nodes. The IM associated with sAH and noAH could be distinguished by differences in bacterial abundance and composition. Key deleterious species were associated with sAH while the Faecalibacterium genus was associated with noAH. Ursodeoxycholic acid was more abundant in faeces from noAH mice. Additionally, in conventional mice humanised with the IM from an sAH patient, a second subsequent transfer of IM from an noAH patient improved alcohol-induced liver lesions. CONCLUSIONS: Individual susceptibility to ALD is substantially driven by IM. It may, therefore, be possible to prevent and manage ALD by IM manipulation.

Human uncoupling protein gene: structure, comparison with rat gene, and assignment to the long arm of chromosome 4.

The uncoupling protein (UCP) gene encodes a unique mammalian mitochondrial proton carrier that induces heat production in brown adipocytes. Human UCP gene was isolated and its organization analyzed. A comparison was made with rat UCP gene. Human UCP gene spans 13 Kb and contains a transcribed region that covers 9 Kb of the human genome. All of the exons were also sequenced except the extreme end of the 3' untranslated region. Two Kb DNA upstream the TATA box were also sequenced. This region contains several fragments that are highly homologous to the gene of rat UCP. Neither CCAAT sequence nor Sp 1 binding motif were detected. Human UCP gene is split into six exons. The complete amino acid sequence of the protein was determined. Human UCP has 305 amino acids and a molecular weight of 32,786. It has no N-terminal targeting sequence. It is 79% homologous to rat UCP both at nucleotidic and amino acid levels. The primary structure of UCP is significantly homologous to the primary structure of the human T1 ADP/ATP carrier, particularly in the C-terminal extremity, which is supposed to contain a nucleotide-binding site in both proteins. Human UCP gene is single type, as it is in rodents. Two genomic fragments were used to detect a 1.9 Kb mRNA in human perirenal brown adipose tissue. Using in situ hybridization, UCP gene was assigned in humans to chromosome 4 in q31. Interestingly, the T1 gene encoding the heart-skeletal muscle ADP/ATP carrier has recently been shown to be on the same chromosome (Li et al. Biol Chem 264:13998, 1989).

Detection of brown adipose tissue uncoupling protein mRNA in adult patients by a human genomic probe.

1. Studies on human brown adipose tissue require specific molecular probes. A human genomic library has been screened with a complementary DNA corresponding to the uncoupling protein (UCP) of rat brown adipose tissue mitochondria. 2. Two recombinant phages were isolated, carrying genomic sequences of human UCP. From them we have subcloned a 0.5 kilobase fragment. This fragment, H-Ucp-0.5, contained two intronic regions and two exonic regions. Exonic regions encoded a sequence of 84 amino acids which exhibited a strong homology with central domain at rat UCP. The organization of H-Ucp-0.5 was confirmed by SI mapping analysis. 3. A Southern analysis suggested that the gene is single type in the human, as it is in rodents. 4. In Northern analysis experiments, H-Ucp-0.5 detected a specific 1.8 kb mRNA in human brown adipose tissue obtained from six patients with phaeochromocytoma and from one patient with a hibernoma. This molecular probe is a new, sensitive and reliable tool with which to study human brown adipocytes.