Welcome to Genomics Revolution. I’m Taylor Yamamoto from the 2019 Hiram College Genetics course hosting this episode on the genome of the bacteria Escherichia Coli O157:H7. I will be calling it E. Coli from now on. This strain of E. Coli is the most harmful strain to humans because it produces a toxin, called Shiga toxin, that causes bloody diarrhea and hemolytic-uremic syndrome, which is when red blood cells get damaged, and then cause a blockage in the kidneys. This can lead to life-threatening kidney failure. Comparatively, nonpathogenic E. Coli often inhabit the human gut without any adverse affects. E. Coli O157:H7 is normally spread fecal-orally, and has caused major gastrointestinal illness outbreaks in both North America and Asia. In this podcast, we will be focusing on the genomic sequence of the E. Coli O157:H7 strainthat caused an outbreak in Sakai City, Osaka, Japan in 1996. 

 

The complete sequence of the chromosome is 5,498,450 base pairs in length. Additionally, the strain also has a large virulence plasmid that is 92,721 base pairs, and a cryptic plasmid that is 3,306 base pairs. In total, the genome is 5,594,477 base pairs long. The Sakai strain is 859,000 base pairs longer than the nonpathogenic strain of E. Coli, but its not like its just tacked onto the end of the sequence. There is a lot of the sequence that is conserved between the two strains, which probably represents the chromosome backbone that most E. Coli strains share, but there are also regions that are unique to the Sakai strain. 

 

In order to cause an infection, bacteria first need to stick to the tissues they are hoping to infect. This is done via fimbriae, which act kind of like Velcro and help the bacteria stick to its target tissue. On the Sakai chromosome, there were fourteen regions that were identified in association with the production of this fimbriae. Five were conserved in the nonpathogenic strain, five were partially conserved in the nonpathogenic strain, and four were unique to the Sakai strain. One of the genes found in this region was actually found to be similar to a gene that codes for fimbriaein Salmonella. 

 

The genomic sequencing of the Sakai strain can be used in the future identification and study of this harmful E. Coli strain. For example, it was used by Gadri et al when their lab was investigating the effects the presence of other bacteria can have on the proliferation rates of various strains of E. Coli O157:H7. 

Because there have been multiple gastrointestinal illness outbreaks worldwide, Manning et al (3) have developed a system to identify SNPs in various strains of E. Coli and how they correspond to level of severity of the infection. 

 

So, while this is definitely an international issue, you listening to this podcast is the first step in furthering education, and coming to a better solution. So thanks for listening. 

 

 

References:

(1) Marouani-Gadri, N., Augier, G., and Carpentier, B. (2009). Characterization of bacterial strains isolated from a beef-processing plant following cleaning and disinfection – Influence of isolated strains on biofilm formation by Sakai and EDL 933 E. Coli O157:H7. Retrieved from https://www.sciencedirect.com/science/article/pii/S0168160509002499?via%3Dihub.

(2) Hayashi, T., Makino, K., Ohnishi, M., Kurokawa, K., Ishii, K., Yokoyama, K., Han, C.G., Ohtsubo, E., Nakayama, K., Murata, T., Tanaka, M., Tobe, T., Iida, T., Takami, H., Honda, T., Sasakawa, C., Ogasawara, N., Yasunaga, T., Kuhara, S., Shiba, T., Hattori, M., and Shinagawa, H. (2001). Complete Genome Sequence of EnterohemorrhagicEschelichia coli O157:H7 and Genomic Comparison with a Laboratory Strain K-12. Retrieved from https://www.ncbi.nlm.nih.gov/pubmed/11258796.

(3) Manning, S., Motiwala, A., Springman, A., Qi, W., Lacher, D., Ouellette, L., Mladonicky, J., Somsel, P., Rudrik, J., Dietrich, S., Zhang, W., Swaminathan, B., Alland, D., and Whittam, T. (2007). Variation in virulence among Clades of Escherichia Coli O157:H7 associated with disease outbreaks. Retrieved from https://www.pnas.org/content/105/12/4868.