B. fragilis group is the most commonly isolated Bacteroidaceae in anaerobic infections, especially those that originate from the gastrointestinal flora. B. fragilis is the most prevalent organism in the B. fragilis group, accounting for 41% to 78% of the isolates of the group. The B. fragilis group is the species of Bacteroidaceae isolated with greatest frequency in clinical specimens. These organisms are resistant to penicillin by virtue of production of beta-lactamase, and by other unknown factors.
This organism was formerly classified as subspecies of B. fragilis (i.e. ssp. fragilis, ssp. distasonis, ss. ovatus, ss. thetaiotaomicron, and ss. vulgatus). They have been reclassified into distinct species on the basis of DNA homology studies. B. fragilis (formerly known as B. fragilis ssp. fragilis, one of the subspecies of B. fragilis) is often recovered from blood, pleural fluid, peritoneal fluid, wounds and brain abscesses.
Although B. fragilis group is the most common species found in clinical specimens, it is the least common Bacteroides present in fecal flora, comprising only 0.5% of the bacteria present in stool. The pathogenicity of this group of organisms probably results from its ability to produce capsular material, which is protective against phagocytosis.
It acts primarily at the surface of the mucosa. It predominates in bacteremia associated with intraabdominal infections, peritonitis and abscesses following rupture of viscus, and subcutaneous abscesses or burns near the anus.
|Classification and external resources|
Working with lab cultures and mice, Johns Hopkins scientists have found a strain of the common gut pathogen Bacteroides fragilis causes colon inflammation and increases activity of a gene for the enzyme superoxide dismutase in the intestine. The effect is to expose the gut to hydrogen peroxide – the caustic, germ-fighting substance found in many medicine cabinets—and cause DNA damage, contributing to the formation of colon tumors, say the scientists.
In general, B. fragilis is susceptible to metronidazole, carbapenems, tigecycline, beta-lactam/beta-lactamase inhibitor combinations (e.g., Unasyn, Zosyn), and certain antimicrobials of the cephamycin class, including cefoxitin. The bacteria have inherent high-level resistance to penicillin. Production of beta lactamase appears to be the main mechanism of antibiotic resistance in B. fragilis. Clindamycin is no longer recommended as the first-line agent for B. fragilis due to emerging high-level resistance (>30% in some reports).
Polysaccharide A (PSA) from these bacteria is reported to be involved in the protection of experimental colitis induced by Helicobacter hepaticus. Further research into B. fragilis PSA has shown it intermediates in several markers of a healthy mammalian immune system: the levels of CD4 T cells, the balance of T-helper cytokines, the presence of well-defined follicular structures in the spleen, and in the inflammatory gut response to pathogens. It is also used for separating carbohydrate groups that classify the group type of the blood cells. The enzyme GalNAC-ase cleaves the A blood cells into O type blood cells, which gives opportunity to produce universal blood units.
- Snydman DR, Jacobus NV, McDermott LA, et al. (January 2010). "Lessons learned from the anaerobe survey: historical perspective and review of the most recent data (2005–2007)". Clin. Infect. Dis. 50 (Suppl 1): S26–33. doi:10.1086/647940. PMID 20067390. http://www.cid.oxfordjournals.org/cgi/pmidlookup?view=long&pmid=20067390.
- Baron EJ, Allen SD (June 1993). "Should clinical laboratories adopt new taxonomic changes? If so, when?". Clin. Infect. Dis. 16 (Suppl 4): S449–50. doi:10.1093/clinids/16.Supplement_4.S449. PMID 8324167. http://www.cid.oxfordjournals.org/cgi/pmidlookup?view=long&pmid=8324167.
- Wexler HM (October 2007). "Bacteroides: the good, the bad, and the nitty-gritty". Clin. Microbiol. Rev. 20 (4): 593–621. doi:10.1128/CMR.00008-07. PMC 2176045. PMID 17934076. http://cmr.asm.org/cgi/pmidlookup?view=long&pmid=17934076.
- Bacteroides infections at eMedicine
- Kuwahara T, Yamashita A, Hirakawa H, et al. (October 2004). "Genomic analysis of Bacteroides fragilis reveals extensive DNA inversions regulating cell surface adaptation". Proc. Natl. Acad. Sci. U.S.A. 101 (41): 14919–24. doi:10.1073/pnas.0404172101. PMC 522005. PMID 15466707. http://www.pnas.org/cgi/pmidlookup?view=long&pmid=15466707.
- Brook I (June 2010). "The role of anaerobic bacteria in bacteremia". Anaerobe 16 (3): 183–9. doi:10.1016/j.anaerobe.2009.12.001. PMID 20025984. http://linkinghub.elsevier.com/retrieve/pii/S1075-9964(09)00173-5.
- Brook I (October 2008). "Microbiology and management of abdominal infections". Dig. Dis. Sci. 53 (10): 2585–91. doi:10.1007/s10620-007-0194-6. PMID 18288616.
- Ayala, J.; Quesada, A.; Vadillo, S.; Criado, J.�n.; Píriz, S. (2005). "Penicillin-binding proteins of Bacteroides fragilis and their role in the resistance to imipenem of clinical isolates". Journal of Medical Microbiology 54 (11): 1055. doi:10.1099/jmm.0.45930-0.
- Mandell GL, Bennett JE, Dolin R (2004). Principles and Practice of Infectious Diseases (6th ed.). Churchill Livingstone. ISBN 0-443-06643-4.
- Brook I (December 2007). "Treatment of anaerobic infection". Expert Rev Anti Infect Ther 5 (6): 991–1006. doi:10.1586/1478722.214.171.1241. PMID 18039083. http://www.future-drugs.com/doi/abs/10.1586/14787126.96.36.1991?url_ver=Z39.88-2003&rfr_id=ori:rid:crossref.org&rfr_dat=cr_pub%3dpubmed.
- Mazmanian SK, Round JL, Kasper DL (May 2008). "A microbial symbiosis factor prevents intestinal inflammatory disease". Nature 453 (7195): 620–5. doi:10.1038/nature07008. PMID 18509436. http://www.nature.com/nature/journal/v453/n7195/abs/nature07008.html.
- Mazmanian SK. "The Microbial Health Factor: Just one molecule can make the difference in mediating a healthy immune response. Surprisingly, it comes from bacteria". The Scientist 23 (8): 34. http://www.the-scientist.com/article/display/55864/.
- Mazmanian SK, Liu CH, Tzianabos AO, Kasper DL (July 2005). "An immunomodulatory molecule of symbiotic bacteria directs maturation of the host immune system". Cell 122 (1): 107–18. doi:10.1016/j.cell.2005.05.007. PMID 16009137. http://linkinghub.elsevier.com/retrieve/pii/S0092-8674(05)00451-4.
- Daniels G, Withers SG (April 2007). "Towards universal red blood cells". Nat. Biotechnol. 25 (4): 427–8. doi:10.1038/nbt0407-427. PMID 17420747.
To request an improvement, please leave a comment on the page. Thank you!