Bacteroides fragilis
Classification
Kingdom: Bacteria
Phylum: Bacteroidetes
Class: Bacteroidia
Order: Bacteroidales
Family: Bacteroidaceae
Genus: Bacteroides
Species: Bacteroides fragilis
Introduction
Bacteroides fragilis (BF) is a Gram-negative bacterium found in the human colon.[1] Although it is relatively rare compared to other species of Bacteroides, it is the most common clinical isolate.[2] Enterotoxigenic B. fragilis (ETBF) is responsible for a large number of opportunistic infections in hospitals and contributes significantly to morbidity and mortality; however, non-enterotoxigenic B. fragilis (NTBF) has been studied as a potential probiotic. In addition to opportunistic infections, BF has been known to cause complications such as colorectal cancer and cholitis.[3] This bacterium is of interest to researchers because of its ability to evade immune responses and evolving drug resistance, as well as its potential activity as a beneficial organism in the human microbiome.
Genetics
Diagnosis with ETBF is confirmed by using PCR to determine the presence of genes coding for B. fragilis toxins.[4] There are no fewer than three variants of the bft gene that codes for these toxins. Although these three variants are all nearly identical, together they code for at least 25 different sequences for the final protein product. In addition, sequencing the genome of one strain B. fragilis has revealed numerous stretches of inverted DNA, creating a vast array of potential configurations of the outer membrane.[1] This extensive diversity allows B. fragilis as a species to evade attempts by the immune system to recognize and destroy it.
A single stretch of DNA approximately 6,000 base pair long distinguishes enterotoxic from nontoxic strains of B. fragilis.[5] This 6-kb region contains not only the bft gene, but also a 700-bp series of promotors.
Microbiome
Enterotoxic Strains
Conclusion
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References
- ↑ Kuwahara, et al. "Genomic analysis of Bacteroides fragilis reveals extensive DNA inversions regulating cell surface adaptation." Proceedings of the National Academy of Sciences 101.41 (2004): 14919-14924.
- ↑ Salyers, A. A. (1984) Annu. Rev. Microbiol. 38, 293-313.
- ↑ Carolyn Redondo, Maria, et al. "Attributable mortality of bacteremia associated with the Bacteroides fragilis group." Clinical infectious diseases 20.6 (1995): 1492-1496.
- ↑ Sears, Cynthia L. "Enterotoxigenic Bacteroides fragilis: a rogue among symbiotes." Clinical microbiology reviews 22.2 (2009): 349-369.
- ↑ Moncrief, J. S., A. J. Duncan, R. L. Wright, L. A. Barroso, and T. D. Wilkins. 1998. Molecular characterization of the fragilysin pathogenicity islet of enterotoxigenic Bacteroides fragilis. Infect. Immun. 66:1735-1739.
Edited by James Cawthon, student of Joan Slonczewski for BIOL 116 Information in Living Systems, 2019, Kenyon College.
