1. E. coli O157:H7 and E. coli O26:H11 are two different serotypes of EHEC. Alth
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Question
1. E. coli O157:H7 and E. coli O26:H11 are two different serotypes of EHEC. Although they share the characteristic of being able to cause hemorrhagic colitis and HUS, they are otherwise only distantly related to one another (no more closely related on average than to any other E. coli strain) (10 pts.). a. What genetic information have each of these serotypes acquired that make them EHEC?b. What is the main evidence supporting the hypothesis that each of these serotypes evolved from a distinct progenitor that belonged to the EPEC group of diarrheagenic E. coli?
c. Is your answer to B an example of parallel, convergent, or divergent evolution? Please explain your answer. 1. E. coli O157:H7 and E. coli O26:H11 are two different serotypes of EHEC. Although they share the characteristic of being able to cause hemorrhagic colitis and HUS, they are otherwise only distantly related to one another (no more closely related on average than to any other E. coli strain) (10 pts.). a. What genetic information have each of these serotypes acquired that make them EHEC?
b. What is the main evidence supporting the hypothesis that each of these serotypes evolved from a distinct progenitor that belonged to the EPEC group of diarrheagenic E. coli?
c. Is your answer to B an example of parallel, convergent, or divergent evolution? Please explain your answer. 1. E. coli O157:H7 and E. coli O26:H11 are two different serotypes of EHEC. Although they share the characteristic of being able to cause hemorrhagic colitis and HUS, they are otherwise only distantly related to one another (no more closely related on average than to any other E. coli strain) (10 pts.). a. What genetic information have each of these serotypes acquired that make them EHEC?
b. What is the main evidence supporting the hypothesis that each of these serotypes evolved from a distinct progenitor that belonged to the EPEC group of diarrheagenic E. coli?
c. Is your answer to B an example of parallel, convergent, or divergent evolution? Please explain your answer.
Explanation / Answer
Answer a) Genetic information received from these serotypes that make them EHEC are:
Enterohaemorrhagic Escherichia coli (EHEC) O26:H11 have emerged as the most important non-O157:H7 EHEC, with respect to their ability to cause diarrhoea and the haemolytic uraemic syndrome (HUS). HUS is a leading cause of acute renal failure in children, and is mainly caused by EHEC expressing Shiga toxins (Stx) 1 and/or 2. Since 1996, EHEC O26, which produce Stx2 only and appear to have enhanced virulence, have been increasingly isolated from HUS patients in Germany. In contrast, EHEC O26 found in cattle predominantly produce Stx1 as the sole Stx. Additional potential virulence factors of EHEC O26 include cytolysins (EHEC hemolysin), serine proteases (EspP), lymphotoxins (Efal) and adhesins (intimin). The genes encoding the virulence factors are located within pathogenicity islands (eae, efa1), bacteriophages (stx) or plasmids (EHEC-hlyA, espP). In addition, EHEC O26 possess, in contrast to other EHEC, the "high pathogenicity island" (HPI), which is also present in pathogenic Yersiniae. This island contains genes involved in the biosynthesis, regulation and transport of the siderophore yersiniabactin. Comparative genomic analyses between EHEC O26 and non-pathogenic E. coli, as well as investigations of mechanisms involved in the transfer of virulence genes, provide a deeper insight into the evolution of EHEC O26. These studies demonstrate how horizontal transfer of virulence genes, even from distantly related organisms, can lead in brief intervals to the rise of a highly virulent clone within a particular E. coli serotype.
Answer b) E. coli O:H serotyping by agglutination of somatic and flagellar antigens by the use of anti-E. coli polyclonal antiserum is time consuming, expensive, and available only in a small number of reference laboratories. E. coli O:H serotyping of pathogens may be required, however, for proper diagnosis and treatment, to maximize an isolate's usefulness for surveillance and to determine overall disease trends. PCR-based methodologies to detect or identify pathogenic E. coli O26 strains have targeted virulence genes such as Shiga toxin (stx) and intimin (eae), flagellar H-antigen genes fliC-fliA, and the O-antigen O26 wzx genes.
PCR methods targeting O26 O-antigen or H11 fliC genes could substitute for serotyping. We therefore developed a molecular serotyping method to target the somatic and flagellar antigens and to allow clinical laboratories to accurately serotype E. colias O26 and/or H11 by multiplex PCR (mPCR).
Answer c) Answer to option B supports paralle evolution as Parallel evolution leads to development of a similar trait that are related, but distinct, species descending from the same ancestor, but from different clades.
Similarly, O26 and H11 serotyped E. coli strains targets the same genes, hence we can say that these sterotypes belong to parallel evolution.
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