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M Tibayrenc

Publications and source records attributed to M Tibayrenc.

At least 73 records · Page 4Linked to original sources
PubMed1998

Beyond strain typing and molecular epidemiology: integrated genetic epidemiology of infectious diseases.

In the past 20 years, genetic and molecular methods for characterizing pathogen strains have taken a major place in modern approaches to epidemiology of parasitic and other infectious diseases. Here, Michel Tibayrenc explains the main concepts used in this field of research, with special emphasis on the approaches developed in his team, and suggests future avenues to explore.

Journal Article↗
PubMed1998

Comparison of chromosome and isoenzyme polymorphism in geographical populations of Leishmania (Viannia) peruviana.

Five chromosomes and 17 isoenzyme loci were analysed in 4 allopatric populations of Leishmania (Viannia) peruviana, and molecular distances calculated with 2 estimators, Chromosomal Size Difference Index and Jaccard Distance. Chromosome and isoenzyme data were in overall concordance: 13/30 isolates clustered similarly on the dendrograms constructed from the different estimators, and a significant correlation (P < 0.001) was observed between the molecular distances calculated from the two sets of characters. This indicates an evolutionary association between chromosomal size polymorphism and isoenzymes. Chromosomes have a faster molecular clock than isoenzymes; twice as many genotypes were identified by chromosome analysis and significant size differences (for a total of up to 500 kb for 5 chromosomes together) were observed within a given zymodeme. Chromosomes most likely represent better indicators of genetic drift than isoenzymes, as suggested by the higher correlation between both estimators of chromosomal size-polymorphism and eco-geography. Some chromosomes might present an adaptive response to environmental variation.

Animals↗
PubMed1998

Population structure of Andean Triatoma infestans: allozyme frequencies and their epidemiological relevance.

Triatoma infestans (Hemiptera: Reduviidae) from 22 Andean localities in Bolivia (n = 968) and Peru (n = 37) were analysed by multi-locus enzyme electrophoresis. Among 12 gene-enzyme systems analysed, GPD, 6GPD and PGM were polymorphic, ACON, G6PD, GPI, 1DH, LAP, MDH, ME, PEP-A and PEP-B were monomorphic. Allozyme frequencies were analysed in relation to geographical and climatic factors, and the presence or absence of Trypanosoma cruzi infection. At one locality (Vallegrande, Bolivia), the frequency of 6Pgd-1 was significantly higher in infected (41% of 85) than in uninfected (17% of 83) adult T. infestans, although no such difference was found among nymphs (n = 347). From other localities, only insects infected with T. cruzi were subjected to isozyme analysis. Populations of T. infestans within villages showed panmixia, while genetic differentiation of T. infestans between villages was correlated with the distance between them. The genetic structure of T. infestans natural populations followed an 'isolation by distance' model, involving a series of founder effects followed by genetic drift, rather than adaptation in response to differential selection pressures. This conforms with circumstantial evidence that T. infestans spread, mainly in association with recent human migrations, from a source, probably in southern Bolivia. Isoenzyme characterization of populations of T. infestans could be used to infer sources of re-infestation during the surveillance phase of control programs.

Animals↗
PubMed1998

Smallness of the panmictic unit of Triatoma infestans (Hemiptera: Reduviidae).

The population genetic structure of Triatoma infestans (Klug), the principal vector of the causative agent of Chagas disease in Bolivia, was investigated by enzyme electrophoresis at 15 loci, of which 3 were polymorphic. A total of 1,286 adults and nymphs was collected from 19 localities of the Cochabamba (high endemicity) and La Paz (low endemicity) departments. Previous results were confirmed, including a low level of polymorphism (0.20), low genetic distance between geographic areas, and a population structure compatible with an isolation by distance model. However, a high proportion (26.3%) of the surveyed localities showed a significant excess of homozygotes, disputing previous conclusions that considered the village as the probable panmictic unit. The excess of homozygotes was reduced when smaller subunits, such as individual houses or chicken coops, were considered, indicating a Wahlund effect.

Animals↗
PubMed1998

The gp63 gene locus, a target for genetic characterization of Leishmania belonging to subgenus Viannia.

In the present study the gp63 gene locus was used as a target for genetic characterization of Leishmania parasites by 2 methods: (i) RFLP analysis with several restriction enzymes (gp63-RFLP), and (ii) intra-genic PCR amplification coupled with restriction analysis (PCR-RFLP). Both methods were applied to a large number of natural isolates belonging to 4 species of the subgenus Viannia, namely L. (V.) braziliensis, L. (V.) peruviana, L. (V.) guyanensis and L. (V.) lainsoni; reference stocks of subgenus Leishmania were included as outgroups. Multilocus isoenzyme typing (MLEE) was used as a reference. On the one hand gp63-RFLP evidenced an extensive polymorphism and revealed specific markers for subgenus, species and geographical populations: congruence with MLEE was demonstrated statistically. The particular interest of gp63-RFLP was illustrated by infra-specific polymorphism, because of the possible relationship with phenotype diversity. On the other hand intra-genic amplification was less resolutive than gp63-RFLP, but also allowed discrimination of the 2 subgenera (PCR alone) and all the species tested in the subgenus Viannia (PCR-RFLP). PCR-RFLP presents an important operational advantage as it allows genetic characterization of minute amounts of parasites, using Leishmania specific primers. The polymorphism revealed by gp63-RFLP and PCR-RFLP illustrates the very high genomic and genetic plasticity of gp63 genes.

Animals↗
PubMed1997

Impact of clonal evolution on the biological diversity of Trypanosoma cruzi.

Trypanosoma cruzi, the agent of Chagas' disease, exhibits considerable biological variability. Moreover, it has been postulated that populations of this protozoan are subdivided into natural clones, which can be separated from each other by considerable levels of evolutionary divergence. The authors have proposed that this long-term clonal evolution may have a profound impact on Trypanosoma cruzi biological diversity. In order to test this hypothesis, 16 T. cruzi stocks representing 3 major clonal genotypes of the parasite were analysed for 8 different in vitro biological parameters. The overall results show a strong statistical linkage between genetic and biological differences. This is in agreement with the working hypothesis, although a notable biological variability is observable among the stocks of each of the 3 major clonal genotypes. The authors propose that T cruzi genetic variability must be taken into account in any applied study dealing with this parasite.

Alleles↗
PubMed1997

Classification of plant trypanosomatids (Phytomonas spp.): parity between random-primer DNA typing and multilocus enzyme electrophoresis.

The genetic polymorphism of 30 isolates of plant trypanosomatids colloquially referred to as plant trypanosomes was assayed by means of RAPD. The principle objectives of this study were to assess the discriminative power of RAPD analysis for studying plant trypanosomes and to determine whether the results obtained were comparable with those from a previous isoenzyme (MLEE) study. The principle groups of plant trypanosomes identified previously by isoenzyme analysis--intraphloemic trypanosomes, intralaticiferous trypanosomes and trypanosomes isolated from fruits--were also clearly separated by the RAPD technique. Moreover, the results showed a fair parity between MLEE and RAPD data (coefficient of correlation = 0.84) and the two techniques have comparable discriminative ability. Most of the separation revealed by the two techniques between the clusters was associated with major biological properties. However, the RAPD technique gave a more coherent separation than MLEE because the intraphloemic isolates, which were biologically similar in terms of their specific localization in the sieve tubes of the plant, were found to be in closer groups by the RAPD. For both techniques, the existence of the main clusters was correlated with the existence of synapomorphic characters, which could be used as powerful tools in taxonomy and epidemiology.

Animals↗
PubMed1997

Isoenzyme diversity in Pneumocystis carinii from rats, mice, and rabbits.

Pneumocystis carinii is an opportunistic pathogen that causes pneumonia in immunocompromised patients. To investigate the genetic diversity of P. carinii populations, multilocus enzyme electrophoresis was used to analyze five enzyme systems (malate dehydrogenase, glucose phosphate isomerase, leucine aminopeptidase, malic enzyme, and 6-phosphogluconate dehydrogenase). Only five different multilocus associations (zymodemes) were recorded for the 70 isolates studied. While only one multilocus combination was found in mice and rabbits, three different multilocus associations were recorded in rats. Population genetic tests and phylogenetic analysis strongly suggest that P. carinii genotypes are host-specific, in agreement with molecular study results, and that no genetic exchange occurs between genotypes from different host species. This hypothesis could be verified only by the evolutionary genetic approach, which relies here on multilocus analysis.

Animals↗
PubMed1997

Metric differences between silvatic and domestic Triatoma infestans (Heteroptera: Reduviidae) in Bolivia.

One hundred and fifty-seven specimens of Bolivian Triatoma infestans (Klug 1834), including 44 from the silvatic focus at Cochabamba (Bolivia), were compared using morphometric characters of the head capsule. From these specimens, 10 silvatic and 28 domestic adults were also compared using additional morphometric characters of the membranous part of the hemelytra. Nonparametric univariate comparisons between specimens from silvatic and domestic ecotopes indicated the importance of the postocular region as a possible diagnostic character for nymphs and adults from the different ecotopes, and they detected wing differences in males. Populations became more distinct entities when head or wing characters were considered jointly in canonical variate analysis. Regardless of whether size variation was considered, canonical variate analysis generally showed greater significance for wing than for head features. These morphological differences between silvatic and domestic bugs, particularly unrelated to size differences, are interpreted to indicate incipient separation between silvatic and domestic populations that had not been detected by previous isoenzyme analyses, and suggest a reinterpretation of the epidemiological significance of silvatic populations of T. infestans in Bolivia.

Analysis of Variance↗
PubMed1997

Leishmania infantum is clonal in AIDS patients too: epidemiological implications.

OBJECTIVE: To test, in AIDS patients, a previously proposed hypothesis of clonal population structure in Leishmania infantum, the agent of visceral leishmaniasis. DESIGN: Forty-three stocks of L. infantum isolated from AIDS patients in Spain were analysed by multilocus enzyme electrophoresis. METHODS: The results were analysed in terms of population genetics according to previously described statistical methods. Departures from panmixia were examined by linkage disequilibrium analysis. RESULTS: As previously shown in HIV-negative patients, classical manifestations of clonality were shown, namely strong linkage disequilibrium, over-representation of genotypes and overall lack of genotype diversity. The same dominant clonal genotype (MON1) was recorded in both HIV-positive and HIV-negative patients. Frequency of this dominant genotype was not statistically different in HIV-positive and HIV-negative patients. CONCLUSIONS: The parasite population under survey appears to be clonal; parasite genotypes can therefore be equated to natural clones, stable in space and time, which can be used as multilocus epidemiological markers. Nevertheless, additional studies are required to better estimate the long-term stability of these clonal genotypes and the possible interference of gene exchange at an evolutionary scale.

AIDS-Related Opportunistic Infections↗
PubMed1997

Parity among the randomly amplified polymorphic DNA method, multilocus enzyme electrophoresis, and Southern blot hybridization with the moderately repetitive DNA probe Ca3 for fingerprinting Candida albicans.

Randomly amplified polymorphic DNA (RAPD) analysis, multilocus enzyme electrophoresis (MLEE), and Southern blot hybridization with moderately repetitive DNA probes have emerged as effective fingerprinting methods for the infectious fungus Candida albicans. The three methods have been compared for their capacities to identify identical or highly related isolates, to cluster weakly related isolates, to discriminate between unrelated isolates, and to assess microevolution within a strain. By computing similarity coefficients between 29 isolates from three cities within the continental United States, strong concordance of the results is demonstrated for RAPD analysis, MLEE, and Southern blot hybridization with the moderately repetitive probe Ca3, and weaker concordance of the results is demonstrated for these three fingerprinting methods and Southern blot hybridization with the moderately repetitive probe CARE2. All methods were also demonstrated to be able to resolve microevolution within a strain, with the Ca3 probe exhibiting the greatest resolving power. The strong correlations demonstrated between polymorphic markers assessed by the four independent fingerprinting methods and the nonrandom association between loci demonstrated by RAPD analysis and MLEE provide evidence for strong linkage disequilibrium and a clonal population structure for C. albicans. In addition, a synapomorphic allele, Pep-3A, was found to be present in all members of one of the three clusters discriminated by RAPD analysis, MLEE, and Ca3 fingerprinting, supporting the concordance of the clustering capacities of the three methods, the robustness of the clusters, and the clonal nature of the clusters.

Adaptor Proteins, Vesicular Transport↗
PubMed1997

Population structure of Trypanosoma brucei S. L. in Cote d'Ivoire assayed by multilocus enzyme electrophoresis: epidemiological and taxonomical considerations.

Fifty-two Trypanosoma brucei stocks isolated in Côte d'Ivoire from sympatric locations were analyzed by cellulose acetate electrophoresis of isoenzymes. Of 13 genetic loci surveyed, 5 appeared as variable, which made it possible to delimit 12 different zymodemes. The most abundant zymodeme involved stocks isolated from both humans and pigs, which is consistent with the hypothesis that pig is a reservoir of human African trypanosomiasis in Côte d'Ivoire, as already proposed by other authors. Population genetic analysis of the isozyme data indicated a strong linkage disequilibrium, which suggests that genetic recombination is severely restricted in this sample and favors the hypothesis that the trypanosome populations surveyed are basically clonal. Nevertheless, additional studies are required to better estimate the long-term stability of these clones and the possible interference of gene exchange at an evolutionary scale. The results corroborate the hypothesis that a majority of human T. brucei stocks from West Africa correspond to a fairly homogeneous cluster of genotypes (T. brucei gambiense 'Group I', Gibson, 1986).

Alleles↗
PubMed1997

Trypanosoma cruzi: evaluation of a RAPD synapomorphic fragment as a species-specific DNA probe.

A methodological approach is proposed to select rapidly DNA sequences characterized by a well defined specificity and potentially interesting to be used as diagnostic probes or as taxonomic and phylogenetic markers. A fragment amplified from a diversified sample of Trypanosoma cruzi stocks by the RAPD (random amplified polymorphic DNA) method with the A8 primer, previously found to be monomorphic in all stocks, was separated in 2 fragments using polyacrylamide electrophoresis. RFLP (restriction fragment length polymorphism) analysis of the 750-bp fragment common to all stocks revealed some sequence heterogeneity within the T. cruzi species, whereas hybridization experiments showed a high homology between fragments amplified from different T. cruzi stocks. These results suggest that sequence analysis will allow the design of internal primers to be used as probes to target specific taxonomic levels (clone, family of related clones, or species) and for diagnosis.

Animals↗
PubMed1996

Trypanosoma brucei s.l: evolution, linkage and the clonality debate.

The Index of Association (IA) has been proposed by Maynard Smith et al. (1993) as a general method for characterizing the population structures of microorganisms as either: clonal, epidemic, cryptic species or panmictic. With reference to the current debate surrounding the mode of reproduction in parasitic protozoa, this study explores (i) the suitability and limitations of the IA for characterizing populations of Trypanosoma brucei s.l., and (ii) the idea that the significance of genetic differences between populations may be better understood if the evolution, spread and temporal stability of certain parasite genotypes are also considered. Four populations of T. brucei from Côte d'Ivoire, Uganda and Zambia are analysed using the IA and a complementary test for linkage disequilibrium, test f of Tibayrenc, Kjellberg & Ayala (1990). The two populations from Uganda are characterized as epidemic, while the others appear more or less clonal; the merits of the two methods are compared. The implications of the various population classifications are discussed with reference to genotype longevity in each region; the evolution and biomedical consequences of the genetic non-homogeneity of T. brucei are reviewed.

Africa↗
PubMed1996

Towards a unified evolutionary genetics of microorganisms.

I propose here that evolutionary genetics, apart from improving our basic knowledge of the taxonomy and evolution of microbes (either eukaryotes or prokaryotes), can also greatly contribute to applied research in microbiology. Evolutionary genetics provides convenient guidelines for better interpreting genetic and molecular data dealing with microorganisms. The three main potential applications of evolutionary genetics in microbiology are (a) epidemiological follow-up (with the necessity of evaluating the stability of microbial genotypes over space and time); (b) taxonomy in the broad sense (better definition and sharper delimitation of presently described taxa, research of hidden genetic subdivisions); and (c) evaluation of the impact of the genetic diversity of microbes on their relevant properties (pathogenicity, resistance to drugs, etc). At present, two main kinds of population structure can be distinguished in natural microbial populations: (a) species that are not subdivided into discrete phylogenetic lineages (panmictic species or basically sexual species with occasional bouts of short-term clonality fall into this category); (b) species that are strongly subdivided by either cryptic speciation or clonal evolution. Improvements in available statistical methods are required to refine these distinctions and to better quantify the actual impact of gene exchange in natural microbial populations. Moreover, a codified selection of markers with appropriate molecular clocks (in other words: adapted levels of resolution) is sorely needed to answer distinct questions that address different scales of time and space: experimental, epidemic, and evolutionary. The problems raised by natural genetic diversity are very similar for all microbial species, in terms of both basic and applied science. Despite this fact, a regrettable compartmentalization among specialists has hampered progress in this field. I propose a synthetic approach, relying on the statistical improvements and technical standardizations called for above, to settle a unified evolutionary genetics of microorganisms, valid whatever the species studied, whether eukaryotic (parasitic protozoa and fungi) or prokaryotic (bacteria). Apart from benefits for basic evolutionary research, the anticipated payoff from this synthetic approach is to render routine and common-place the use of microbial evolutionary genetics in the fields of epidemiology, medicine, and agronomy.

Animals↗