[{"data":1,"prerenderedAt":-1},["ShallowReactive",2],{"$fxLN3MUwXCdr5RPjwZYIDpOj8CHyjOmngWTgoKXPtZbg":3,"$fp4R3cOSrZse7noqXEMkCW1_5X_INcarCcXQuVga0VVc":32,"$f3Ft0rKFJHppdzE-vuveecxx1BUcg9iOlMLtyzf_MJDg":47},[4,8,12,16,20,24,28],{"title":5,"slug":6,"path":7},"About Microbeonline.com","about-microbeonline-com","\u002Fabout-microbeonline-com\u002F",{"title":9,"slug":10,"path":11},"About Me","about-me","\u002Fabout-microbeonline-com\u002Fabout-me\u002F",{"title":13,"slug":14,"path":15},"Advertise with Us","advertise-us","\u002Fadvertise-us\u002F",{"title":17,"slug":18,"path":19},"Privacy Policy","privacy-policy","\u002Fprivacy-policy\u002F",{"title":21,"slug":22,"path":23},"Abbreviations","abbreviations","\u002Fabbreviations\u002F",{"title":25,"slug":26,"path":27},"Microbes","microbes","\u002Fmicrobes\u002F",{"title":29,"slug":30,"path":31},"Books","recommended-books","\u002Frecommended-books\u002F",{"type":33,"data":34},"blog",{"slug":35,"title":36,"description":36,"seoTitle":37,"seoDescription":37,"author":38,"createdDate":39,"lastUpdatedDate":40,"draft":41,"category":42,"image":37,"body":43,"faq":44,"tags":45,"related":46},"bacteroides-fragilis-properties-pathogenesis-lab-diagnosis","Bacteroides fragilis: Properties, Pathogenesis, Lab Diagnosis",null,"Acharya Tankeshwar","2021-04-29","2025-12-29",false,"bacteriology","### General Characteristics\n\n- Gram-negative, non-spore-forming, non-motile, pleomorphic bacilli; appearing as slender rods or coccobacillus forms.\n- Obligate anaerobe\n- It is also probably the most frequent anaerobe isolated from clinical specimens.\n\n![Bacteroides fragilis](https:\u002F\u002Fassets.microbeonline.com\u002Fblogs\u002FBacteroides-fragilis-feature.jpg)Figure: *Bacteroides fragilis*\n\n### Habitat\n\nIt is the most common commensal in the human intestine. Members of the *Bacteroides fragilis* group make up a significant proportion of the normal microbiota of the GI tract (10^11 to 10^12 CFU\u002Fg feces).\n\n### Virulence Factors\n\nMembers of the *Bacteroides fragilis* group are responsible for a variety of clinical infections, but the species *B. fragilis* has the highest incidence. A number of virulence factors have been demonstrated to explain the enhanced virulence and pathogenicity of this particular species:\n\n- **agglutinins** and **fimbriae** provide adhesion ability;\n- the **capsule** protects against the host immune response by evading [phagocytosis](\u002Fphagocytosis-mechanism-and-steps\u002F);\n- mechanisms to ameliorate oxygen toxicity; and,\n- destruction of host tissue via production of **histiocytic enzymes**.\n\n### Disease\n\n*B. fragilis* causes **peritonitis** following bowel injury and pelvic inflammatory disease (PID). It is also implicated in abdominal infections, brain abscesses, and empyema (pyothorax or purulent pleuritis). Enterotoxigenic strains can cause diarrhea.\n\n![anaerobic infections - Common locations of infections involving anaerobic bacteria(Image source: Koneman, Ref-1)](https:\u002F\u002Fassets.microbeonline.com\u002Fblogs\u002FAnaerobic-infections-of-our-body.png)Figure: Common locations of infections involving anaerobic bacteria(Image source: Koneman, Ref-1)\n\nAs members of the *B. fragilis* group constitute a significant proportion of the microbiota of the GI tract; breaks in the GI mucosa by trauma or GI or GU surgery allows entry of these bacteria and consequent intra-abdominal infections, if appropriate prophylaxis is not commenced. *B.fragilis* is most commonly responsible for intra-abdominal abscesses and sepsis but is also involved in gynecological abscesses, skin and soft tissue infections, pericarditis (as a result of hematogenous spread to the heart), bacteremia often associated with malignancies or in postsurgical infections, and rare instances of endocarditis, meningitis, and septic arthritis.\n\n### Laboratory Diagnosis\n\nAll clinical specimens must be handled meticulously as brief exposure to oxygen may kill obligate anaerobes and result in failure to isolate them in the laboratory.\n\n**Accepted specimens**\n\n- Tissue bits\n- Necrotic materials\n- Aspirated body fluids\n- Pus in syringes\n\n**Unacceptable specimen for anaerobic culture**\n\n- gastric washings,\n- all swabs\n- midstream urine,\n- prostatic secretions collected transurethrally,\n- feces (except for the recovery of *Clostridioides difficile*),\n- throat, nose, or other oropharyngeal specimens (except specimens obtained from the deep tissue during oral surgery),\n- superficial skin, and environmental cultures\n\n#### Transport\n\nSpecimens should be immediately put into [RCM broth](\u002Frobertsons-cooked-meat-medium-principle-composition-procedure-and-uses\u002F) or other anaerobic transport media and brought to the laboratory as soon as possible.\n\n#### Gram Stain\n\nAll clinical specimens from suspected anaerobic infections should be Gram stained and examined for characteristic morphology.\n\n![Gram-negative, Bacteroides fragilis subsp. fragilis - Gram-negative,Bacteroides fragilissubsp.fragilis(Image source: CDC\u002F Don Stalons)](https:\u002F\u002Fassets.microbeonline.com\u002Fblogs\u002FBacteriodes-fragilis-gram-negative-anaerobic-rod.jpg)Figure: Gram-negative, Bacteroides fragilis subsp.fragilis(Image source: CDC\u002F Don Stalons)\n\n> Many times in clinical laboratories, anaerobic gram-negative bacilli that grow on Bacteroides fragilis selective media (like Bacteroides bile esculin) may be reported out as “B. fragilis group”; so it is difficult to know how common some of the other members are in infections. With the increased use of molecular methods and MALDI-TOF in the future, we should expect to be able to better determine what species really are involved in clinical infections.\n\n#### Culture & Identification\n\nSamples should be processed immediately under anaerobic conditions which can be created by [various methods.](\u002Ftag\u002Fanaerobiosis\u002F) Anaerobic cultures should be performed routinely only on tissues or aspirated fluid\u002Fpus.\n\n> Never perform anaerobic cultures on specimens from sites that may be contaminated with mucosal flora or feces\n\nVarious [culture media can be used for the isolation of anaerobes](\u002Fcommonly-used-anaerobic-media-for-anaerobic-bacteriology\u002F), such as:\n\n- Anaerobic blood agar\n- Neomycin blood agar\n- Egg yolk agar\n- Phenlethyl agar (PEA)\n- BHIS agar: Brain-Heart infusion agar added with supplements, such as vitamin K and hemin\n- Bacterioides bile esculin agar (BBE agar)\n\nIsolates are identified on the basis of\n\n- Colony morphology,\n- Gram staining characteristics\n- Biochemical tests\n- Susceptibility to antibiotic disks\n- Gas-liquid chromatography etc.\n\n### Antimicrobial Susceptibility\n\n*B. fragilis* group isolates produce β-lactamases and consequently are resistant to penicillin (ampicillin, amoxicillin) and most cephalosporins, but are usually susceptible to ampicillin-sulbactam and piperacillin-tazobactam. They are uniformly susceptible to metronidazole and carbapenems, but increasingly resistant to clindamycin.\n\n### References and Further Readings\n\n1. Procop, G. W., & Koneman, E. W. (2016). [Koneman’s Color Atlas and Textbook of Diagnostic Microbiology](https:\u002F\u002Famzn.to\u002F2vRkUvk)(Seventh, International edition). Lippincott Williams and Wilkins.\n2. Tille, P. (2017). *Bailey & Scott’s Diagnostic Microbiology* (14 edition). Mosby.",[],[],[],[48,54,61,66,70,74,79,84,88,92],{"slug":49,"name":38,"description":50,"image":51,"body":52,"postCount":53},"acharya-tankeshwar","Editor-in-chief","https:\u002F\u002Fassets.microbeonline.com\u002Fauthors\u002Ftankeshwar-acharya-author-microbeonline.jpg","***Tankeshwar Acharya, MSc (Medical Microbiology)***\n\n*Tankeshwar Acharya is an Assistant Professor in the Department of Microbiology at Patan Academy of Health Sciences (PAHS), Nepal, where he has been teaching and practicing clinical microbiology for over 14 years. He is the founder of Microbe Online, one of the leading free microbiology education resources on the web, covering bacteriology, mycology, parasitology, immunology, and clinical laboratory diagnostics written from direct experience in both the classroom and the diagnostic laboratory.*",433,{"slug":55,"name":56,"description":57,"image":58,"body":59,"postCount":60},"ashma-shrestha","Ashma Shrestha","SEO Copywriter and Science Communicator\nKathmandu, Nepal","https:\u002F\u002Fassets.microbeonline.com\u002Fauthors\u002Fashma-shrestha.png","Ashma Shrestha holds a Master of Science in Medical Microbiology from the Institute of Science and Technology (IOST), Tribhuvan University, Nepal, where she developed a strong foundation in virology, molecular biology, and diagnostic microbiology.\n\nShe now works as an SEO Copywriter at Resolution Digital, where she combines her scientific training with research-driven content strategy. She is certified in Google Analytics and Google Business Profile (GBP), and brings a data-informed approach to science communication writing content that is not only accurate but structured to reach and serve the students who need it most.\n\nAt microbeonline, Ashma contributes articles primarily in virology and molecular biology, areas she finds most compelling for their mechanistic depth and their growing clinical relevance. Her writing reflects the same standard the site is built on: factual rigor, clear explanation of the *why* behind microbiology concepts, and content that helps students move from memorization to genuine understanding.\n\nShe is passionate about making complex microbiological concepts accessible without sacrificing accuracy; a skill that sits at the intersection of her scientific training and her professional work in content and SEO.",81,{"slug":62,"name":63,"description":64,"image":37,"body":37,"postCount":65},"sushmita-baniya","Sushmita Baniya","Author \u002F Contributor",32,{"slug":67,"name":68,"description":64,"image":37,"body":37,"postCount":69},"samikshya-acharya","Samikshya Acharya",20,{"slug":71,"name":72,"description":64,"image":37,"body":37,"postCount":73},"alisha-tripathi","Alisha Tripathi",6,{"slug":75,"name":76,"description":77,"image":37,"body":37,"postCount":78},"aastha-shrestha","Aastha Shrestha"," Author \u002F Contributor",10,{"slug":80,"name":81,"description":82,"image":37,"body":37,"postCount":83},"guest-author","Guest Author","Guest Author \u002F Contributor",2,{"slug":85,"name":86,"description":64,"image":37,"body":37,"postCount":87},"srijana-khanal","Srijana Khanal",18,{"slug":89,"name":90,"description":82,"image":37,"body":37,"postCount":91},"dr-poonam-acharya","Dr. Poonam Acharya",1,{"slug":93,"name":94,"description":64,"image":37,"body":95,"postCount":96},"nisha-rijal","Nisha Rijal","**Nisha Rijal** is a microbiologist and quality assurance specialist. She served for nearly 12 years as a microbiologist at the National Public Health Laboratory (NPHL), Nepal's national reference laboratory, and continues to work as a consultant microbiologist in international public health organization. ",51]