Usual transaminase values: should they be reviewed and adjusted? / Valeurs usuelles des transaminases : faut-il les réexaminer et les adapter ?

Alanine (ALT) and aspartate aminotransferases (AST) are intracellular enzymes involved in the metabolism of amino acids. The measurements of their activities are two of the most ordered tests in clinical laboratories, used to screen, diagnose and follow diseases affecting the liver. Recent works highlighted that reference values for ALT and AST vary according to the analytical method and the individual's characteristics, like with many other biomarkers. Reference values for ALT show clinically significant differences according to the analytical method (higher when supplementing samples with phosphate pyridoxal), gender (higher in males than in females), body mass index (positive correlation), and age (higher in infants and the elderly), but not according to ethnicity or employed analyzer. According to the analytical method and age, reported reference values for AST show clinically significant differences, similar to ALT. These observations prove clinical laboratories' interest in updating their reference values according to sex, body mass index, age (especially when providing testing to pediatric or elderly populations), and the analytical method employed. If possible, a standardized method should be used, including sample supplementation with pyridoxal phosphate, to ensure the comparability of results between laboratories.

L'aspartate aminotransférase (ASAT) et l'alanine aminotransférase (ALAT) sont des enzymes intracellulaires impliquées dans le métabolisme des acides aminés. La mesure de leurs activités fait partie des examens biochimiques les plus couramment réalisés en pratique clinique, en particulier pour le dépistage, le diagnostic et le suivi des pathologies hépatiques. Les valeurs de référence de l'ALAT et de l'ASAT varient en fonction des caractéristiques individuelles et de la méthode d'analyse. Dans cet article, nous proposons une brève revue de ces sources de variations pour répondre à la question suivante : faut-il réexaminer et adapter les valeurs usuelles des transaminases ? Les valeurs usuelles rapportées pour l'ALAT montrent des différences cliniquement significatives selon la méthode analytique (plus élevées lors de l'emploi de phosphate pyridoxal), le sexe (plus élevées chez l'homme que chez la femme), l'indice de masse corporelle (corrélation positive) et l'âge (plus élevées chez les nourrissons et les personnes âgées). Ces études ne montrent pas de différences en fonction de l'origine ethnique ou de l'analyseur employé. Concernant l'ASAT, les valeurs usuelles rapportées montrent des différences cliniquement significatives selon la méthode analytique et l'âge, similaires à celles observées pour l'ALAT. Une méthode standardisée doit être utilisée de préférence, intégrant notamment l'emploi de phosphate de pyridoxal, pour assurer la comparabilité des résultats entre les laboratoires. Ces observations prouvent la nécessité pour les laboratoires cliniques d'actualiser leurs valeurs usuelles en fonction du sexe, de l'indice de masse corporelle, de l'âge (notamment pour les âges extrêmes : populations pédiatriques ou âgées) et de la méthode analytique employée.

Biofilm Structures in a Mono-Associated Mouse Model of Clostridium difficile Infection.

Clostridium difficile infection (CDI) is a major healthcare-associated disease with high recurrence rates. Host colonization is critical for the infectious process, both in first episodes and in recurrent disease, with biofilm formation playing a key role. The ability of C. difficile to form a biofilm on abiotic surfaces is established, but has not yet been confirmed in the intestinal tract. Here, four different isolates of C. difficile, which are in vitro biofilm producers, were studied for their ability to colonize germ-free mice. The level of colonization achieved was similar for all isolates in the different parts of the murine gastrointestinal tract, but pathogen burden was higher in the cecum and colon. Confocal laser scanning microscopy revealed that C. difficile bacteria were distributed heterogeneously over the intestinal tissue, without contact with epithelial cells. The R20291 strain, which belongs to the Ribotype 027 lineage, displayed a unique behavior compared to the other strains by forming numerous aggregates. By immunochemistry analyses, we showed that bacteria were localized inside and outside the mucus layer, irrespective of the strains tested. Most bacteria were entrapped in 3-D structures overlaying the mucus layer. For the R20291 strain, the cell-wall associated polysaccharide PS-II was detected in large amounts in the 3-D structure. As this component has been detected in the extrapolymeric matrix of in vitro C. difficile biofilms, our data suggest strongly that at least the R20291 strain is organized in the mono-associated mouse model in glycan-rich biofilm architecture, which sustainably maintains bacteria outside the mucus layer.

The Clostridium difficile Protease Cwp84 Modulates both Biofilm Formation and Cell-Surface Properties.

Clostridium difficile is responsible for 15-20% of antibiotic-associated diarrheas, and nearly all cases of pseudomembranous colitis. Among the cell wall proteins involved in the colonization process, Cwp84 is a protease that cleaves the S-layer protein SlpA into two subunits. A cwp84 mutant was previously shown to be affected for in vitro growth but not in its virulence in a hamster model. In this study, the cwp84 mutant elaborated biofilms with increased biomass compared with the parental strain, allowing the mutant to grow more robustly in the biofilm state. Proteomic analyses of the 630Δerm bacteria growing within the biofilm revealed the distribution of abundant proteins either in cell surface, matrix or supernatant fractions. Of note, the toxin TcdA was found in the biofilm matrix. Although the overall proteome differences between the cwp84 mutant and the parental strains were modest, there was still a significant impact on bacterial surface properties such as altered hydrophobicity. In vitro and in vivo competition assays revealed that the mutant was significantly impaired for growth only in the planktonic state, but not in biofilms or in vivo. Taken together, our results suggest that the phenotypes in the cwp84 mutant come from either the accumulation of uncleaved SlpA, or the ability of Cwp84 to cleave as yet undetermined proteins.

Biofilms of Clostridium species.

The biofilm is a microbial community embedded in a synthesized matrix and is the main bacterial way of life. A biofilm adheres on surfaces or is found on interfaces. It protects bacteria from the environment, toxic molecules and may have a role in virulence. Clostridium species are spread throughout both environments and hosts, but their biofilms have not been extensively described in comparison with other bacterial species. In this review we describe all biofilms formed by Clostridium species during both industrial processes and in mammals where biofilms may be formed either during infections or associated to microbiota in the gut. We have specifically focussed on Clostridium difficile and Clostridium perfringens biofilms, which have been studied in vitro. Regulatory processes including sporulation and germination highlight how these Clostridium species live in biofilms. Furthermore, biofilms may have a role in the survival and spreading of Clostridium species.