RESUMO
Shigella infections account for a considerable burden of acute diarrheal diseases worldwide and remain a major cause of childhood mortality in developing countries. Although, all four species of Shigella (S. dysenteriae, S. flexneri, S. boydii, and S. sonnei) cause bacillary dysentery, historically only S. dysenteriae type 1 has been recognized as carrying the genes for Shiga toxin (stx). Recent epidemiological data, however, have suggested that the emergence of stx carrying S. flexneri strains may have originated from bacteriophage-mediated inter-species horizontal gene transfer in one specific geographical area, Hispaniola. To test this hypothesis, we analyzed whole genome sequences of stx-encoding phages carried by S. flexneri strains isolated in Haiti and S. flexneri S. boydii and S. dysenteriae strains isolated from international travelers who likely acquired the infection in Haiti or the Dominican Republic. Phylogenetic analysis showed that phage sequences encoded in the Shigella strains from Hispaniola were bacteriophage φPOC-J13 and they were all closely related to a phage isolated from a USA isolate, E. coli 2009C-3133 serotype O119:H4. In addition, despite the low genetic heterogeneity of phages from different Shigella spp. circulating in the Caribbean island between 2001 and 2014, two distinct clusters emerged in Haiti and the Dominican Republic. Each cluster possibly originated from phages isolated from S. flexneri 2a, and within each cluster several instances of horizontal phage transfer from S. flexneri 2a to other species were detected. The implications of the emergence of stx-producing non-S. dysenteriae type 1 Shigella species, such as S. flexneri, spans not only the basic science behind horizontal phage spread, but also extends to medical treatment of patients infected with this pathogen.
Assuntos
Bacteriófagos/genética , Bacteriófagos/fisiologia , Toxina Shiga/metabolismo , Shigella flexneri/metabolismo , Shigella flexneri/virologia , República Dominicana/epidemiologia , Disenteria Bacilar/epidemiologia , Disenteria Bacilar/microbiologia , Transferência Genética Horizontal , Variação Genética , Haiti/epidemiologia , Humanos , Filogeografia , Polimorfismo de Nucleotídeo ÚnicoRESUMO
Shiga toxins (Stx) are commonly produced by Shigella dysenteriae serotype 1 and Stx-producing Escherichia coli. However, the toxin genes have been detected in additional Shigella species. We recently reported the emergence of Stx-producing Shigella in travelers in the United States and France who had recently visited Hispaniola (Haiti and the Dominican Republic). In this study, we confirm this epidemiological link by identifying Stx-producing Shigella from Haitian patients attending clinics near Port-au-Prince. We also demonstrate that the bacteriophage encoding Stx is capable of dissemination to stx-negative Shigella species found in Haiti, suggesting that Stx-producing Shigella may become more widespread within that region.
RESUMO
Shiga toxins (Stx) are cytotoxins involved in severe human intestinal disease. These toxins are commonly found in Shigella dysenteriae serotype 1 and Shiga-toxin-producing Escherichia coli; however, the toxin genes have been found in other Shigella species. We identified 26 Shigella flexneri serotype 2 strains isolated by public health laboratories in the United States during 2001-2013, which encode the Shiga toxin 1a gene (stx1a). These strains produced and released Stx1a as measured by cytotoxicity and neutralization assays using anti-Stx/Stx1a antiserum. The release of Stx1a into culture supernatants increased ≈100-fold after treatment with mitomycin C, suggesting that stx1a is carried by a bacteriophage. Infectious phage were found in culture supernatants and increased ≈1,000-fold with mitomycin C. Whole-genome sequencing of several isolates and PCR analyses of all strains confirmed that stx1a was carried by a lambdoid bacteriophage. Furthermore, all patients who reported foreign travel had recently been to Hispañiola, suggesting that emergence of these novel strains is associated with that region.