Bacteroides fragilis: Difference between revisions

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==Introduction==
==Introduction==
<i>Bacteroides fragilis</i> is a Gram-negative bacterium found in the human colon.<ref>[https://www.pnas.org/content/101/41/14919.short 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.]</ref> Although it is relatively rare compared to other species of <i>Bacteroides</i>, it is the most common clinical isolate.<ref>[https://www.ncbi.nlm.nih.gov/pmc/articles/PMC522005/ Salyers, A. A. (1984) Annu. Rev. Microbiol. 38, 293-313.]</ref> Enterotoxigenic <i>B. fragilis</i> (ETBF) is responsible for a large number of opportunistic infections in hospitals and contributes significantly to morbidity and mortality; however, non-enterotoxigenic <i>B. fragilis</i> (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.<ref>[https://academic.oup.com/cid/article-abstract/20/6/1492/477370 Carolyn Redondo, Maria, et al. "Attributable mortality of bacteremia associated with the Bacteroides fragilis group." Clinical infectious diseases 20.6 (1995): 1492-1496.]</ref> This bacterium is of interest to researchers because of its ability to evade immune responses and its evolving drug resistance. Non-virulent strains are also under investigation for possibly having a beneficial effect on the human microbiome.
<i>Bacteroides fragilis</i> is a Gram-negative bacterium found in the human colon.<ref>[https://www.pnas.org/content/101/41/14919.short Kuwahara, et al. <i>Genomic analysis of Bacteroides fragilis reveals extensive DNA inversions regulating cell surface adaptation.</i> Proc. Natl. Acad. Sci. USA 101:14919-14924.]</ref> Although it is relatively rare compared to other species of <i>Bacteroides</i>, it is the most common clinical isolate.<ref>[https://www.annualreviews.org/doi/abs/10.1146/annurev.mi.38.100184.001453 Salyers, A. A. 1984. <i>Bacteroides of the human lower intestinal tract. Annu. Rev. Microbiol. 38:293-313.</i>]</ref> Enterotoxigenic <i>B. fragilis</i> (ETBF) is responsible for a large number of opportunistic infections in hospitals and contributes significantly to morbidity and mortality; however, non-enterotoxigenic <i>B. fragilis</i> (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.<ref>[https://www.ncbi.nlm.nih.gov/pubmed/7548498 Redondo, M. C., M. D. Arbo, J. Grindlinger, and D. R. Snydman. 1995. <i>Attributable mortality of bacteremia associated with the Bacteroides fragilis</i> group. Clin. Infect. Dis. 20:1492-1496.]</ref> This bacterium is of interest to researchers because of its ability to evade immune responses and its evolving drug resistance. Non-virulent strains are also under investigation for possibly having a beneficial effect on the human microbiome.


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Diagnosis with ETBF is confirmed by using PCR to determine the presence of genes coding for <i>B. fragilis</i> toxins.<ref>[https://www.ncbi.nlm.nih.gov/pubmed/19366918 Sears, Cynthia L. "Enterotoxigenic Bacteroides fragilis: a rogue among symbiotes." Clinical microbiology reviews 22.2 (2009): 349-369.]</ref> There are no fewer than three variants of the <i>bft</i> 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 <i>B. fragilis</i> has revealed numerous stretches of inverted DNA, creating a vast array of potential configurations of the outer membrane.[1] This extensive diversity allows <i>B. fragilis</i> as a species to evade attempts by the immune system to recognize and destroy it.<br><br>
Diagnosis with ETBF is confirmed by using PCR to determine the presence of genes coding for <i>B. fragilis</i> toxins.<ref>[https://www.ncbi.nlm.nih.gov/pubmed/19366918 Sears, Cynthia L. "Enterotoxigenic Bacteroides fragilis: a rogue among symbiotes." Clinical microbiology reviews 22.2 (2009): 349-369.]</ref> There are no fewer than three variants of the <i>bft</i> 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 <i>B. fragilis</i> has revealed numerous stretches of inverted DNA, creating a vast array of potential configurations of the outer membrane.[1] This extensive diversity allows <i>B. fragilis</i> as a species to evade attempts by the immune system to recognize and destroy it.<br><br>


A single stretch of DNA approximately 6,000 base pair long distinguishes enterotoxic from nontoxic strains of <i>B. fragilis</i>.<ref>[https://www.ncbi.nlm.nih.gov/pmc/articles/PMC108111/ Moncrief, J. S., A. J. Duncan, R. L. Wright, L. A. Barroso, and T. D. Wilkins. 1998. <i>Molecular characterization of the fragilysin pathogenicity islet of enterotoxigenic Bacteroides fragilis.</i> Infect. Immun. 66:1735-1739.]</ref> This 6-kb region contains not only the <i>bft</i> gene, but also a 700-bp series of promotors.
A single stretch of DNA approximately 6,000 base pair long distinguishes enterotoxic from nontoxic strains of <i>B. fragilis</i>.<ref>[https://www.ncbi.nlm.nih.gov/pmc/articles/PMC108111/ 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 <i>Bacteroides fragilis.</i> Infect. Immun. 66:1735-1739.]</ref> This 6-kb region contains not only the <i>bft</i> gene, but also a 700-bp series of promotors.
==Microbiome==
==Microbiome==
===Enterotoxic Strains===
===Enterotoxic Strains===

Revision as of 23:37, 3 December 2019

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Classification

Kingdom: Bacteria
Phylum: Bacteroidetes
Class: Bacteroidia
Order: Bacteroidales
Family: Bacteroidaceae
Genus: Bacteroides
Species: Bacteroides fragilis

Introduction

Bacteroides fragilis 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 its evolving drug resistance. Non-virulent strains are also under investigation for possibly having a beneficial effect on the human microbiome.



Colony of Bacteroides fragilis, Gram-stained and magnified 1000x. Image taken by Don Stalon. Source: Centers for Disease Control and Prevention

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


Edited by James Cawthon, student of Joan Slonczewski for BIOL 116 Information in Living Systems, 2019, Kenyon College.