Transcriptional profiling of Vibrio cholerae recovered directly from patient specimens during early and late stages of human infection

Abstract

Understanding gene expression by bacteria during the actual course of human infection may provide important insights into microbial pathogenesis. In this study, we evaluated the transcriptional profile of Vibrio cholerae, the causative agent of cholera, in clinical specimens from cholera patients. We collected samples of human stool and vomitus that were positive by dark-field microscopy for abundant vibrios and used a microarray to compare gene expression in organisms recovered directly from specimens collected during the early and late stages of human infection. Our results reveal that V. cholerae gene expression within the human host environment differs from patterns defined in in vitro models of pathogenesis. tcpA, the major subunit of the essential V. cholerae colonization factor, was significantly more highly expressed in early than in late stages of infection; however, the genes encoding cholera toxin were not highly expressed in either phase of human infection. Furthermore, expression of the virulence regulators toxRS and tcpPH was uncoupled. Interestingly, the pattern of gene expression indicates that the human upper intestine may be a uniquely suitable environment for the transfer of genetic elements that are important in the evolution of pathogenic strains of V. cholerae. These findings provide a more detailed assessment of the transcriptome of V. cholerae in the human host than previous studies of organisms in stool alone and have implications for cholera control and the design of improved vaccines.

FIG. 1.

Regional clusters of genes on the V. cholerae large and small chromosomes that display similar patterns of expression during human infection (P < 10⁻⁷). All genes evaluated with the microarray are shown. For each gene, the log₁₀-fold change in expression in early infection (vomit) compared with late infection (stool) is represented graphically. Genes that are more highly expressed in early human infection are represented in red, and genes that are more highly expressed in late human infection are represented in green. Significant clusters of genes are represented in yellow.

FIG. 2.

Differential expression of genes in the TCP island during early compared with late human infection, represented as log₁₀ fold change. Expression of the transposase sequence (tnp) of the TCP island is shown at the left, and that of the integrase gene (int) is at the right. Transcripts in the TCP island that are more highly expressed in early human infection are shown in red, and transcripts that are more highly expressed in late human infection are shown in green. Genes flanking the TCP island are represented in grey. The differential expression of the individual gene tcpA achieved statistical significance after adjustment with the false discovery rate control.