Monod's bacterial growth model revisited.

An attempt to justify Monod's bacterial growth model is presented. The justification is based on a mechanistic approach to growth which leads to a differential equation with delay and then to Monod's model. An unexpected increase of parameter K(s) with µm is predicted by the theory. A survey of literature shows that this effect is present in a large majority of published data.

Object-centered representation for species systematics and identification in living systems in nature.

An artificial intelligence application to identification in biological taxonomy is presented. An object-centered representation is described using SHIRKA, a knowledge-based system developed in France. The capacities of this system, relating to a classification algorithm, are described. An application to the identification of the trees and lianas of the evergreen forests of the Western Ghats (India) is presented to illustrate the problems encountered in the development of the knowledge base. A model of a systematist's reasoning, using evolutionary principles, is the basis of this work. Finally the efficiency of the system is discussed.

[Bacteriostatic and bactericidal antibiotics: differences in subinhibitory concentration effects on the growth of Escherichia coli]. / Antibiotiques bactériostatiques et bactéricides: différences des effets des concentrations subinhibitrices sur la croissance de Escherichia coli.

The growth of Escherichia coli in synthetic medium was mathematically analysed at subinhibitory levels of bactericidal and bacteriostatic antibiotics. Over a threshold of concentration, bactericidal antibiotics induce an unexpected change of growth pattern. Bacteriostatic antibiotics induce a progressive effect linked to a continuously altered growth pattern that still remains close to the controls. This fundamental differential of antibiotic effects is reflecting well-known bacteriostatic or bactericidal phenomena. In vitro this analysis of the growth enables to measure the level of the antibiotic sensitivity. In vivo, these results must be taken into account when subinhibitory concentrations of antimicrobial agent are reached at the infection site.

[An expert system as an aid to the validation of results of the antibiogram. Feasibility study based on the example of Staphylococcus aureus]. / Système expert d'aide à la validation des résultats de l'antibiogramme. Etude de faisabilité sur l'exemple de Staphylococcus aureus.

A model of expert system using Prolog language was developed, to verify the coherence of the results of the antibiotic sensitivity test. Biological knowledge was formalized in three different ways: a credibility coefficient based on epidemiological data is assigned to known observed resistance; co-existent resistances are described with lists of "implicit" resistances, reflecting phenotypes commonly observed within some antibiotic groups; every single or "implicit" resistance is connected to a "gregarius" status, expressing the plasmidic nature of resistance. Applied to Staphylococcus aureus, the expert system is able to detect the inconsistencies of the antibiotic sensitivity test and to identify required knowledges. It therefore allows phenotypic interpretation of results.

[Use of an expert system as a tool to carry out urinary cyto-bacteriologic tests]. / Utilisation d'un système expert d'aide à la réalisation des examens cytobactériologiques urinaires.

An expert system for urine examinations was developed. Its validation was performed in a routine work, by comparison of expert decisions with software conclusions. Results of finished examinations or in progress were taken into account. The agreement was satisfactory. In addition to reliability, advantages constituted by availability, flexibility and adaptability were notified. Repeatability and reproducibility were also emphasized.

[Effect of subinhibitory concentrations of antibiotics on the growth level of bacteria]. / Effet des concentrations subinhibitrices d'antibiotiques sur le taux de croissance des bactéries.

The effect of subinhibitory concentrations of 5 antibiotics on the growth rate of 2 bacteria (Staphylococcus aureus and Escherichia coli) has been studied. Chloramphenicol, dibekacin, netilmicin and nalidixic acid have a direct effect on the growth rate. Apparently, aminoglycosides and nalidixic acid have an accompanying effect on the affinity for the energizing substrate. Amoxicillin does not seem to be concerned by this 2 mechanisms. The interest of the estimation of the growth rate by an adaptative algorithm has been pointed out.

Bacterial growth measurement using an automated system: mathematical modelling and analysis of growth kinetics.

The reliability of automated systems was assessed by simultaneously using an MS2 and a methodology of data interpretation/mathematical modelling. Two experimental situations were analysed. Bacterial growth both in synthetic and in complex media could be well described by Monod's model and the logistic model. In the two cases, the fit of the models to the data was satisfactory.

Codon catalog usage and the genome hypothesis.

Frequencies for each of the 61 amino acid codons have been determined in every published mRNA sequence of 50 or more codons. The frequencies are shown for each kind of genome and for each individual gene. A surprising consistency of choices exists among genes of the same or similar genomes. Thus each genome, or kind of genome, appears to possess a "system" for choosing between codons. Frameshift genes, however, have widely different choice strategies from normal genes. Our work indicates that the main factors distinguishing between mRNA sequences relate to choices among degenerate bases. These systematic third base choices can therefore be used to establish a new kind of genetic distance, which reflects differences in coding strategy. The choice patterns we find seem compatible with the idea that the genome and not the individual gene is the unit of selection. Each gene in a genome tends to conform to its species' usage of the codon catalog; this is our genome hypothesis.

Dynamics of macromolecular populations: a mathematical model of the quantitative changes of RNA in the silkgland during the last larval instar.

The quantitative changes of RNA in the silkgland of Bombyx mori have been studied during the last larval instar by using a mathematical model (Volterra-Kostitzin model). This model can be associated with a global mechanism including synthesis and degradative processes. The numerical and statistical methods used for model analysis are described in an appendix. Thus we have compared the accumulation of total RNA (essentially ribosomal) after a treatment (juvenile hormone) and between several strains. The importance of the degradative factor is denoted to explain the observed differences, whereas the synthesis rates remain relatively stable. The last observation may lead us to an interpretation of the molecular effect of a selection to increase silk production : rather than an increase of the productivity of cellular machinery, the degradative process has been limited.