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For microbial pathogens, phylogeographic differentiation seems to be relatively common. However, the neutral population structure of Salmonella enterica serovar Typhi reflects the continued existence of ubiquitous haplotypes over millennia. In contrast, clinical use of fluoroquinolones has yielded at least 15 independent gyrA mutations within a decade and stimulated clonal expansion of haplotype H58 in Asia and Africa. Yet, antibiotic-sensitive strains and haplotypes other than H58 still persist despite selection for antibiotic resistance. Neutral evolution in Typhi appears to reflect the asymptomatic carrier state, and adaptive evolution depends on the rapid transmission of phenotypic changes through acute infections.

Original publication




Journal article



Publication Date





1301 - 1304


Adaptation, Physiological, Africa, Alleles, Anti-Bacterial Agents, Asia, Biological Evolution, Carrier State, DNA Gyrase, Drug Resistance, Bacterial, Drug Resistance, Multiple, Bacterial, Fluoroquinolones, Genes, Bacterial, Genetic Variation, Haplotypes, Humans, Molecular Sequence Data, Mutation, Polymorphism, Genetic, Polymorphism, Single Nucleotide, Salmonella typhi, Selection, Genetic, Typhoid Fever