Segmented Filamentous Bacteria

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Module Name: sfb
Module Title: Segmented Filamentous Bacteria
Image Info: Electron micrograph, XX,XXX magnification.
Created by: Lynn Bry
Date: Dec. 12th, 1996.


Key points: segmented filamentous bacteria | apical microvilli | actin accumulation | host cytoplasm |

Introduction: Electron-micrograph of the proximal ends of three segmented filamentous bacteria associated with a villus enterocyte. Adult mouse ileum.


actin_accumulation: Actin has been identified in the electron-dense region of host cytoplasm forming around the head piece of the SFB. No function or role has been attributed to this accumulation.

apical_microvilli: Apical microvilli of the enterocyte. These finger-like structures greatly increase the surface area of the intestinal epithelium, allowing for better absorption of nutrients. Actin filaments form the structural core of each microvillus. The filaments interweave with the underlying terminal web of actin which runs beneath the microvilli and associates with cytoplasmic components in the cytoskeletom.

Note that the association with the SFB does not disrupt surrounding microvilli. This event is in contrast to the attachment of pathogens such as salmonella typhimurium which disrupt the microvilli.

host_cell's_cytoplasm: The cytoplasm appears relatively unaffected by the microbial intrusion. In some cases an accumulation of mitochondria may be seen surrounding the electron-dense area that develops around the microbial head piece.

segmented_filamentous_bacteria: Head unit of segmented filamentous bacteria - Candiatus arthromitus - Gram-positive anaerobic microbes. The SFB represent a unique component of the indigenous gut flora. The microbes specifically colonize the ileal epithelium. The first head piece of the organism inserts in the apical membrane of villus-associated enterocytes. Note that the interaction does not disrupt surrounding apical microvilli, contrasting with the effects produced by pathogens such as Salmonella typhimurium.

A series of 'box car' shaped cells follows the head piece, creating a long filamentous organism that spans the length of many enterocytes . Distally located cells undergo sporulation, releasing spores into the intestinal lumen. rRNA analyses indicate the SFB are closely related to the clostridia. However, little is known about their life cycle, or methods of adherence to differentiated enterocytes.

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