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Biomedical subjects

E A McGraw

Publications and source records attributed to E A McGraw.

6 recordsLinked to original sources
PubMed2002

Wolbachia density and virulence attenuation after transfer into a novel host.

The factors that control replication rate of the intracellular bacterium Wolbachia pipientis in its insect hosts are unknown and difficult to explore, given the complex interaction of symbiont and host genotypes. Using a strain of Wolbachia that is known to over-replicate and shorten the lifespan of its Drosophila melanogaster host, we have tracked the evolution of replication control in both somatic and reproductive tissues in a novel host/Wolbachia association. After transinfection (the transfer of a Wolbachia strain into a different species) of the over-replicating Wolbachia popcorn strain from D. melanogaster to Drosophila simulans, we demonstrated that initial high densities in the ovaries were in excess of what was required for perfect maternal transmission, and were likely causing reductions in reproductive fitness. Both densities and fitness costs associated with ovary infection rapidly declined in the generations after transinfection. The early death effect in D. simulans attenuated only slightly and was comparable to that induced in D. melanogaster. This study reveals a strong host involvement in Wolbachia replication rates, the independence of density control responses in different tissues, and the strength of natural selection acting on reproductive fitness.

Adaptation, Physiological↗
PubMed2001

Wolbachia-mediated sperm modification is dependent on the host genotype in Drosophila.

Estimates of Wolbachia density in the eggs, testes and whole flies of drosophilid hosts have been unable to predict the lack of cytoplasmic incompatibility (CI) expression in so-called mod(-) variants. Consequently, the working hypothesis has been that CI expression, although related to Wolbachia density, is also governed by unknown factors that are influenced by both host and bacterial genomes. Here, we compare the behaviour of the mod(-) over-replicating Wolbachia popcorn strain in its native Drosophila melanogaster host to the same strain transinfected into a novel host, namely Drosophila simulans. We report that (i) the popcorn strain is a close relative of other D. melanogaster infections, (ii) the mod(-) status of popcorn in D. melanogaster appears to result from its inability to colonize sperm bundles, (iii) popcorn is present in the bundles in D. simulans and induces strong CI expression, which demonstrates that the bacterial strain does not lack the genetic machinery for inducing CI and that there is host-species-specific control over Wolbachia tissue tropism, and (iv) infection of sperm bundles by the mod(-) D. simulans wCof strain indicates that there are several independent routes by which a strain can be a CI non-expressor.

Animals↗
PubMed1999

Clonal relationship among invasive and non-invasive strains of enteroinvasive Escherichia coli serogroups.

The genetic relatedness among 96 invasive Escherichia coli belonging to several serogroups and 13 non-invasive of several serotypes that share the same O antigen was investigated by multilocus enzyme electrophoresis analysis. The invasive strains were isolated in different parts of the world and most of them recovered from dysentery. Twenty-nine electrophoretic types were distinguished and the most invasive strains were found to belong to two major lineages. These results suggested that the invasive ability in these strains has evolved in divergent chromosomal backgrounds, presumably through the horizontal spread of plasmid-borne invasion genes. The maintenance of invasive phenotypes in separate lineages suggests that this ability confers a selective advantage to invasive strains.

Dysentery↗
PubMed1999

Evolution of Wolbachia pipientis transmission dynamics in insects.

Wolbachia pipientis is an intracellular bacterial parasite of arthropods that enhances its transmission by manipulating host reproduction, most commonly by inducing cytoplasmic incompatibility. The discovery of isolates with modified cytoplasmic incompatibility phenotypes and others with novel virulence properties is an indication of the potential breadth of evolutionary strategies employed by Wolbachia.

Animals↗
PubMed1999

Molecular evolution and mosaic structure of alpha, beta, and gamma intimins of pathogenic Escherichia coli.

Two types of pathogenic Escherichia coli, enteropathogenic E. coli (EPEC) and enterohemorrhagic E. coli (EHEC), cause diarrheal disease by disrupting the intestinal environment through the intimate attachment of the bacteria to the intestinal epithelium. This process is mediated by intimin, an outer membrane protein that is homologous to the invasins of pathogenic Yersinia. The intimin (eae) gene is part of a pathogenicity island, a 35-kb segment of DNA that has been acquired independently in different groups of pathogens. Nucleotide sequences of eae of three EPEC and four EHEC strains representing distinct clonal lineages revealed an exceptionally high level of divergence (15%) in the amino acid sequences of alpha, beta, and gamma intimin molecules, most of which is concentrated in the C-terminal region. The gamma intimin sequences from E. coli strains with serotypes O157:H7, O55:H7, and O157:H- are virtually identical, supporting the hypothesis that these bacteria belong to a single clonal lineage. Sequences of beta intimin of EPEC strains of serotypes O111:H2 and O128:H2 show substantial differences from alpha and gamma intimins, indicating that these strains have evolved independently. Strong nonrandom clustering of polymorphic sites indicates that the intimin genes are mosaics, suggesting that protein divergence has been accelerated by recombination and diversifying selection.

Adhesins, Bacterial↗