Transcriptional Profiling of Vibrio cholerae Recovered Directly from Patient Specimens during Early and Late Stages of Human Infection

Department of Immunology and Infectious Diseases, Harvard University, Cambridge, Massachusetts, United States
Infection and Immunity (Impact Factor: 3.73). 09/2005; 73(8):4488-93. DOI: 10.1128/IAI.73.8.4488-4493.2005
Source: PubMed


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.

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Available from: Abu Syed Golam Faruque
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    • "While V. cholerae virulence induction has been vigorously studied in the past two decades and is characterized to some extent, repression of virulence once it has been established is not well understood. Downregulation of virulence genes including those encoding TCP and CT during the late period of infection (in 'rice water' stool from cholera patients) has been observed (Merrell et al., 2002; Larocque et al., 2005; Nelson et al., 2008) and has been proposed to be important for environmental survival. For V. cholerae to terminate virulence gene expression, two events must occur: (i) activation of the toxT promoter must be curtailed and (ii) activation of the tcpA promoter autoregulatory loop that produces ToxT must be curtailed. "
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    ABSTRACT: Vibrio cholerae is the causative agent of cholera, a severe diarrhoeal illness. V. cholerae produces two major virulence factors: the cholera toxin, which directly causes diarrhoea, and the toxin-coregulated pilus, which is required for intestinal colonization. Production of these virulence factors is dependent on the major virulence regulator, ToxT. Under virulence-inducing growth conditions, transcription factors ToxR and TcpP initially activate transcription of toxT. However, once ToxT has been expressed, it produces more of itself independent of ToxR and TcpP by activating transcription of the long tcpA operon, within which toxT is located. It is known that V. cholerae terminates virulence gene expression prior to escape from the host, but it is unknown how this ToxT-positive feedback loop is broken, an essential step in terminating virulence gene expression. To better understand how ToxT protein activity is regulated, we monitored ToxT accumulation and activity under virulence-inducing and -repressing growth conditions. Our results suggest that ToxT protein undergoes proteolytic degradation to terminate virulence gene expression. This directed degradation of ToxT supports a model for terminating V. cholerae virulence gene expression late in infection, with both ToxT and TcpP undergoing proteolysis prior to escape from the host.
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    • "The correlation between replicate cultures grown in LB and sequenced by Helicos and Illumina, respectively, was somewhat lower (R = 0.73), suggesting some platform-specific biases. The range of reads per ORF in the Illumina and Helicos datasets varied between 0 and greater than 100,000 and 8,000, respectively , reflecting a far more robust and sensitive dynamic measurement of expression than previously obtained in microarray-based approaches (Merrell et al., 2002; Xu et al., 2003; Bina et al., 2003; Larocque et al., 2005). "
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    • "The bacteria secrete cholera toxin (CT) that, when internalized by epithelial cells of the small intestine, causes major water efflux into the gut lumen (Sack et al., 2004). As a result, V. cholerae leaves the human host during diarrheal purges (Larocque et al., 2005). "
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    ABSTRACT: Vibrio cholerae, the marine bacterium responsible for the diarrheal disease cholera, utilizes a multitude of virulence factors to cause disease. The importance of two of these factors, the toxin co-regulated pilus (TCP) and cholera toxin (CT), has been well documented for pandemic O1 and epidemic O139 serogroups. In contrast, endemic non-O1 and non-O139 serogroups can cause localized outbreaks of cholera-like illness, often in the absence of TCP and CT. One virulence mechanism used by these strains is the type VI secretion system (T6SS) to export toxins across the cell envelope and confer toxicity toward eukaryotic and prokaryotic organisms. The V. cholerae strain V52 (an O37 serogroup strain) possesses a constitutively active T6SS and was responsible for an outbreak of gastroenteritis in Sudan in 1968. To evaluate a potential role of the T6SS in the disease cholera, we compared the T6SS clusters of V. cholerae strains with sequenced genomes. We found that the majority of V. cholerae strains, including one pandemic strain, contain intact T6SS gene clusters; thus, we propose that the T6SS is a conserved mechanism that allows pandemic and endemic V. cholerae to persist both in the host and in the environment.
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