Abstract
BackgroundEpidemics and pandemics of cholera, a diarrheal disease, are attributed to Vibrio cholerae serogroups O1 and O139. In recent years, specific lytic phages of V. cholerae have been proposed to be important factors in the cyclic occurrence of cholera in endemic areas. However, the role and potential participation of lytic phages during long interepidemic periods of cholera in non-endemic regions have not yet been described. The purpose of this study was to isolate and characterize specific lytic phages of V. cholerae O1 strains.MethodsSixteen phages were isolated from wastewater samples collected at the Endhó Dam in Hidalgo State, Mexico, concentrated with PEG/NaCl, and purified by density gradient. The lytic activity of the purified phages was tested using different V. cholerae O1 and O139 strains. Phage morphology was visualized by transmission electron microscopy (TEM), and phage genome sequencing was performed using the Genome Analyzer IIx System. Genome assembly and bioinformatics analysis were performed using a set of high-throughput programs. Phage structural proteins were analyzed by mass spectrometry.ResultsSixteen phages with lytic and lysogenic activity were isolated; only phage ØVC8 showed specific lytic activity against V. cholerae O1 strains. TEM images of ØVC8 revealed a phage with a short tail and an isometric head. The ØVC8 genome comprises linear double-stranded DNA of 39,422 bp with 50.8 % G + C. Of the 48 annotated ORFs, 16 exhibit homology with sequences of known function and several conserved domains. Bioinformatics analysis showed multiple conserved domains, including an Ig domain, suggesting that ØVC8 might adhere to different mucus substrates such as the human intestinal epithelium. The results suggest that ØVC8 genome utilize the “single-stranded cohesive ends” packaging strategy of the lambda-like group. The two structural proteins sequenced and analyzed are proteins of known function.ConclusionsØVC8 is a lytic phage with specific activity against V. cholerae O1 strains and is grouped as a member of the VP2-like phage subfamily. The encoding of an Ig domain by ØVC8 makes this phage a good candidate for use in phage therapy and an alternative tool for monitoring V. cholerae populations.Electronic supplementary materialThe online version of this article (doi:10.1186/s12985-016-0490-x) contains supplementary material, which is available to authorized users.
Highlights
Epidemics and pandemics of cholera, a diarrheal disease, are attributed to Vibrio cholerae serogroups O1 and O139
Isolation of bacteria and phages Thirteen isolates identified in wastewater samples from the Endhó Dam were characterized as V. cholerae non-O1/ O139 (6 isolates), V. alginolyticus (4 isolates), and A. veronii
Our observations showed that ØVC8 is a virulent phage with lytic activity against several V. cholerae O1 strains; none of the identified genes of the ØVC8 genome appear to be involved in bacterial lysis
Summary
Epidemics and pandemics of cholera, a diarrheal disease, are attributed to Vibrio cholerae serogroups O1 and O139. Cholera is a clinical-epidemiologic syndrome caused by ingestion of water contaminated with Vibrio cholera serogroups O1 and O139. This disease is considered an important public health problem worldwide, though it mainly affects developing countries and alters the economies of these regions [1]. A viable but nonculturable state or biofilm is induced, which contributes to adaptation by the bacterium for survival in different environmental conditions [3]. Bacteriophages or phages (bacterial viruses) are mobile genetic elements that participate in horizontal gene transfer in bacteria, thereby contributing to their environmental adaptation and evolution. Several bacterial virulence genes are present in phage genomes, and the mobile nature of phages can promote the emergence of new epidemic strains
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