[How I explore autism spectrum disorder in a child]. / Comment j'explore un trouble du spectre de l'autisme chez l'enfant.

Autism Spectrum Disorder (ASD) is a complex neurodevelopmental trouble characterized by deficits in communication and social interactions associated with restricted and repetitive behaviour, interests and activities. Given the heterogeneity of the disorder and the absence of biomarker, its diagnostic approach must be comprehensive and multidisciplinary, according to international classifications. The aetiology of ASDs remains mostly unknown and results from a multifactorial model. This document offers guidelines to standardize practices and optimize the exploration of children with autism.

Le trouble du spectre de l'autisme (TSA) est une pathologie neurodéveloppementale complexe, caractérisée par des déficits de la communication et des interactions sociales associés à un caractère restreint et répétitif des comportements, des intérêts et des activités. Etant donné le caractère très hétérogène du trouble et l'absence de biomarqueur, son approche diagnostique doit être globale, multidisciplinaire, et répondre aux critères des classifications internationales. Par ailleurs, les TSA résultent d'un modèle multifactoriel dont l'étiologie demeure inconnue dans la majorité des cas. Afin d'optimiser le rendement exploratoire et d'homogénéiser les pratiques, ce document propose un cadre pour la mise au point des TSA en pédiatrie.

The pentose moiety of adenosine and inosine is an important energy source for the fermented-meat starter culture Lactobacillus sakei CTC 494.

The genome sequence of Lactobacillus sakei 23K has revealed that the species L. sakei harbors several genes involved in the catabolism of energy sources other than glucose in meat, such as glycerol, arginine, and nucleosides. In this study, a screening of 15 L. sakei strains revealed that arginine, inosine, and adenosine could be used as energy sources by all strains. However, no glycerol catabolism occurred in any of the L. sakei strains tested. A detailed kinetic analysis of inosine and adenosine catabolism in the presence of arginine by L. sakei CTC 494, a fermented-meat starter culture, was performed. It showed that nucleoside catabolism occurred as a mixed-acid fermentation in a pH range (pH 5.0 to 6.5) relevant for sausage fermentation. This resulted in the production of a mixture of acetic acid, formic acid, and ethanol from ribose, while the nucleobase (hypoxanthine and adenine in the case of fermentations with inosine and adenosine, respectively) was excreted into the medium stoichiometrically. This indicates that adenosine deaminase activity did not take place. The ratios of the different fermentation end products did not vary with environmental pH, except for the fermentation with inosine at pH 5.0, where lactic acid was produced too. In all cases, no other carbon-containing metabolites were found; carbon dioxide was derived only from arginine catabolism. Arginine was cometabolized in all cases and resulted in the production of both citrulline and ornithine. Based on these results, a pathway for inosine and adenosine catabolism in L. sakei CTC 494 was presented, whereby both nucleosides are directly converted into their nucleobase and ribose, the latter entering the heterolactate pathway. The present study revealed that the pentose moiety (ribose) of the nucleosides inosine and adenosine is an effective fermentable substrate for L. sakei. Thus, the ability to use these energy sources offers a competitive advantage for this species in a meat environment.

The kinetics of the arginine deiminase pathway in the meat starter culture Lactobacillus sakei CTC 494 are pH-dependent.

Lactobacillus sakei is frequently present as the dominant lactic acid bacterium in spontaneously fermented meat products, demonstrating its competitiveness in and adaptation to the meat environment. Since meat is generally low in carbohydrate content, the ability to utilize other energy sources to generate ATP, such as arginine via the arginine deiminase (ADI) pathway, represents a competitive benefit. In this study, the kinetics of growth and arginine conversion capabilities of Lb. sakei CTC 494 were analyzed, and a model was set up to describe the influence of pH on growth and arginine conversion. A series of in vitro batch fermentations using reconstituted MRS medium at different constant pH values (pH 4.50-pH 7.75) was performed. Arginine conversion through the ADI pathway, which was activated from the stationary growth phase on, resulted in the production of both citrulline and ornithine for all pH conditions tested. However, the pattern and the ratio of the end-products of the ADI pathway were influenced by pH. For certain pH values (between pH 5.0 and 6.5), a further conversion of citrulline into ornithine was found when all arginine was depleted. Characterization of responses of the ADI pathway in Lb. sakei CTC 494 to environmental conditions will allow a better understanding and control of this important starter culture in meat fermentations.

Biodiversity, ecological determinants, and metabolic exploitation of sourdough microbiota.

Sourdough is a microbial ecosystem of lactic acid bacteria (LAB) and yeasts in a matrix of mainly cereal flour and water. Culture-dependent and culture-independent microbiological analysis together with metabolite target analyses of different sourdoughs enabled to understand this complex fermentation process. It is difficult to link the species diversity of the sourdough microbiota with the (geographical) type of sourdough and the flour used, although the type and quality of the latter is the main source of autochthonous LAB in spontaneous sourdough fermentations and plays a key role in establishing stable microbial consortia within a short time. Carbohydrate fermentation targeted towards maltose catabolism, the use of external alternative electron acceptors, amino acid transamination reactions, and/or the arginine deiminase pathway are metabolic activities that favour energy production, cofactor (re)cycling, and/or tolerance towards acid stress, and hence contribute to the competitiveness and dominance of certain species of LAB found in sourdoughs. Also, microbial interactions play an important role. The availability of genome sequences for several LAB species that are of importance in sourdough as well as technological advances in the fields of functional genomics, transcriptomics, and proteomics enable new approaches to study sourdough fermentations beyond the single species level and will allow an integral analysis of the metabolic activities and interactions taking place in sourdough. Finally, the implementation of selected starter cultures in sourdough technology is of pivotal importance for the industrial production of sourdoughs to be used as flavour carrier, texture-improving, or health-promoting dough ingredient.

The arginine deiminase pathway of Lactobacillus fermentum IMDO 130101 responds to growth under stress conditions of both temperature and salt.

The arginine deiminase (ADI) pathway is a means by which certain sourdough lactic acid bacteria (LAB) convert arginine into ornithine via citrulline while producing ammonia and ATP, thereby coping with acid stress and gaining an energetic advantage. Lactobacillus fermentum IMDO 130101, an isolate from a spontaneous laboratory rye sourdough, possesses an ADI pathway which is modulated by environmental pH. In the present study, a broader view of the activity of the ADI pathway in response to growth under two other commonly encountered stress factors, temperature and added salt, was obtained. In both cases, an increase in ornithine production was observed as a response to growth under both temperature and salt stress conditions. Biokinetic parameters were obtained to describe the kinetics of the ADI pathway as a function of temperature and added salt. The arginine conversion rate increased as a function of added NaCl concentrations but was hardly affected by temperature. In addition, arginine-into-citrulline conversion rate was not affected by temperature but increased with increasing NaCl concentrations. Citrulline-into-ornithine conversion rate increased with increasing temperature, while it dropped to zero with added salt. These findings suggest a more pronounced adaptation of the strain through the ADI pathway to added salt, as compared with different constant temperatures. Furthermore, these results suggest that the ADI pathway in L. fermentum IMDO 130101 is active in adapting to non-optimal growth conditions.

Kinetic analysis of growth and sugar consumption by Lactobacillus fermentum IMDO 130101 reveals adaptation to the acidic sourdough ecosystem.

The effect of pH on growth and carbohydrate metabolism of L. fermentum IMDO 130101 was investigated. Pronounced acid tolerance occurred together with marked responses in sugar metabolism due to acid stress. In accordance with the environment from which this strain was isolated, glucose and fructose metabolism remained active at low pH. Fructose was quantitatively converted into mannitol under all conditions tested, yielding an energetic advantage to the strain. Modelling of growth, sugar consumption, lactic and acetic acid production, and mannitol production of L. fermentum IMDO 130101 allowed the estimation of its basic biokinetic parameters when growing under simulated sourdough conditions. The obtained kinetic data underline the competitiveness of the strain in an acidic environment.

Environmental pH determines citrulline and ornithine release through the arginine deiminase pathway in Lactobacillus fermentum IMDO 130101.

Sourdough lactic acid bacteria (LAB) need to be adapted to a highly acidic and, therefore, challenging environment. Different mechanisms are employed to enhance competitiveness, among which conversion of arginine into ornithine through the arginine deiminase (ADI) pathway is an important one. A combined molecular and kinetic approach of the ADI pathway in Lactobacillus fermentum IMDO 130101, a highly competitive sourdough LAB strain, identified mechanisms with advantageous technological effects and quantified the impact of these effects. First, molecular analysis of the arcBCAD operon of 4.8 kb revealed the genes encoding the enzymes ornithine transcarbamoylase, carbamate kinase, arginine deiminase, and an arginine/ornithine (A/O) antiporter, respectively, with an additional A/O antiporter 702.5 kb downstream of the ADI operon. The latter could play a role in citrulline transport. Second, pH-controlled batch fermentations were carried out, generating data for the development of a mathematical model to describe the temporal evolution of the three amino acids involved in the ADI pathway (arginine, citrulline, and ornithine) as a result of the activity of these enzymes and transporter(s). Free arginine in the medium was converted completely into a mixture of citrulline and ornithine under all conditions tested. However, the ratio between these end-products and the pattern of their formation showed variation as a function of environmental pH. Under optimal pH conditions for growth, citrulline release and some further conversion into ornithine was observed. When growing under sub-optimal pH conditions, ornithine was the main product of the ADI pathway. These kinetic data suggest a role in adaptation of L. fermentum IMDO 130101 to growth under sub-optimal conditions.

Kinetics of growth and 3-methyl-1-butanol production by meat-borne, coagulase-negative staphylococci in view of sausage fermentation.

Five species of meat-borne, coagulase-negative staphylococci were screened for their in vitro production of 3-methyl-1-butanol. The highest production level was encountered for Staphylococcus sciuri alphaSG2, despite its poor growth. With respect to Staphylococcus species that are generally applied in sausage starter cultures, production of 3-methyl-1-butanol was higher with Staphylococcus xylosus 3PA6 than with Staphylococcus carnosus 833. Mathematical modelling was used to link the kinetics of 3-methyl-1-butanol production by S. xylosus 3PA6 and S. carnosus 833 in meat simulation medium to bacterial growth and environmental factors, in casu temperature and pH. The specific production rate of 3-methyl-1-butanol was about ten times higher for S. xylosus 3PA6 than for S. carnosus 833, indicating a higher production rate per amount of biomass. This explains the higher concentrations of 3-methyl-1-butanol in the medium with S. xylosus 3PA6, despite its poorer growth.