[{"data":1,"prerenderedAt":-1},["ShallowReactive",2],{"$fxLN3MUwXCdr5RPjwZYIDpOj8CHyjOmngWTgoKXPtZbg":3,"$fbzISOlaRcv1dok-f9QQZESmHQSKj5izf0C29vERGry0":32,"$f3Ft0rKFJHppdzE-vuveecxx1BUcg9iOlMLtyzf_MJDg":101},[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":47},"bacillus-anthracis-properties-pathogenesis-diagnosis","Bacillus anthracis: Properties, Pathogenesis, Lab Diagnosis",null,"Acharya Tankeshwar","2020-04-21","2026-07-05",false,"bacteriology","*Bacillus anthracis,* the most notorious pathogen of the genus *Bacillus*, is the causative agent of a serious **zoonotic disease** called anthrax. Anthrax is primarily a disease of wild and domestic herbivorous mammals. It is one of the most common agents of **bioterrorism** which was implicated previously in Sverdlovsk anthrax outbreak in 1979 and US postal system attack in 2001.\n\n### General properties\n\n1. Gram-positive, large rectangular rods arranged in chains\n2. Capsulated: *B.anthracis* has a polypeptide [capsule](\u002Fbacterial-capsule-structure-and-importance-and-examples-of-capsulated-bacteria\u002F), made up of polyglutamate (in contrast to the polysaccharide capsule present in most of the other capsulated bacteria). Capsulated bacilli are often square ended (**“box-car”**) in appearance.\n3. Endospore forming: *B. anthracis* has non-bulging spores; that are elliptical and centrally located.\n4. Non-motile, whereas other members of the genus are motile.\n5. Aerobes\n\n![Bacillus anthracis important properties](https:\u002F\u002Fassets.microbeonline.com\u002Fblogs\u002FBacillus-anthracis.jpg)Figure: *Bacillus anthracis* important properties\n\n> Robert Koch isolated Bacillus anthracis for the first time in pure culture and Koch’s postulates were made based on Bacillus anthracis. Louis Pasteur prepared first live attenuated bacterial vaccine, anthrax vaccine.\n\n## Pathogenesis and Clinical Presentations\n\n#### Transmission\n\nBoth humans and animals acquire anthrax infection by ingestion, inhalation or traumatic inoculation of spores of *Bacillus anthracis*. The spores are dormant forms that are found in the soil or in contaminated animal products (e.g., hair or animal hides).\n\n#### Virulence factors of Bacillus anthracis\n\nPathogenesis of anthrax is due to two plasmid-encoded virulence factors; anthrax toxin and capsule encoded in [plasmid](\u002Fplasmids-properties-types-uses\u002F) pXO1 and pXO2 respectively.\n\n**A: Anthrax toxin**: It is a **tripartite exotoxin**, composed of three sub units:\n\n### Clinical presentations\n\nHuman anthrax is mainly divided into four clinical forms, depending up on the mode of acquisition. These forms are:\n\n1. **Cutaneous anthrax:** It accounts for 95-99% of cases worldwide. Infection results from direct inoculation of spores via small cuts or abrasions. The lesions (eschars) are generally found on exposed regions (e.g., hands, arms, neck, wrist, and face) of the body almost invariably accompanied by marked edema. The incubation period ranges from a few hours to 3 weeks, most often 2 to 6 days.\n2. **Oropharyngeal\u002Fgastrointestinal** anthrax: In oropharyngeal anthrax, lesions are seen in buccal cavity, tongue, tonsils or posterior pharyngeal wall whereas lesions are mostly seen in ileum and caecum in gastrointestinal anthrax. Symptoms include sore throat, dysphagia, vomiting, mild diarrhea and fever. These may be mild but are occasionally severe, progressing to haematemesis, bloody diarrhea, and massive ascites. The incubation period ranges from 3 to 7 days.\n3. **Inhalational (pulmonary) anthrax:** Symptoms of pulmonary anthrax include fever or chills, sweats, fatigue or malaise, non-productive cough, dyspnoea, changes in mental state including confusion, and nausea or vomiting. The incubation period ranges from 4-6 days.\n4. **Injectional anthrax:** This is a new form of anthrax reported from injectional-drug users. Symptoms may be similar to those of cutaneous anthrax, but there may be infection deep under the skin or in the muscle where the drug was injected. Injection anthrax can spread throughout the body faster and be harder to recognize and treat.\n\n> Despite its publicity as a potential agent of biologic warfare, B. anthracis is not highly contagious, so BSL 2 practices, containment equipment and facilities are appropriate for diagnostic tests.\n\n## Laboratory diagnosis of Anthrax\n\n#### Sample\n\nSample should be collected before starting antibiotic treatment. The choice of the sample depends on the type of anthrax and clinical presentations. Commonly used specimens are pus, sputum, blood, CSF, gastric aspirate, and feces.\n\n> To isolate Bacillus anthracis from environmental samples, heat or alcohol shock should be given before plating on culture media. The shock will allow only the spore-forming bacilli to survive, thus aiding as an enrichment technique.\n\n#### Direct demonstration\n\n1. **Gram staining**: Reveals Gram-positive, large, rectangular rods. Spores are usually not seen in clinical specimens.\n2. **McFadyean’s reaction:** Polypeptide capsule can be demonstrated by staining with Gurr’s polychrome methylene blue stain for 30 seconds. Capsule appears as amorphous purple material surrounding blue bacilli. This is used for the presumptive diagnosis of animal anthrax.\n3. **Direct immunofluorescence test (direct-IF):** It detects capsular and cell wall polypeptide antigens by using fluorescent-tagged monoclonal antibodies. It is used for confirmation of the diagnosis during bioterrorism outbreaks.\n4. **Ascoli’s thermoprecipitation test**: It is a ring precipitation test, done when the sample is received in putrid form and bacilli are likely to be non-viable. Tissue samples are grounded in saline, boiled and filtered. This antigenic extract is layered over anthrax antiserum on a narrow capillary tube. A ring of precipitate appears at the junction of two liquids within 5 minutes.\n\n#### Culture\n\n*Bacillus anthracis* is aerobic, non-fastidious, grows in ordinary media and has a wide temperature range (12-45°C) of growth. Sporulation is promoted at 25-30°C and in the presence of unfavorable conditions such as distilled water, 2% NaCl, oxalate, and oxygen.\n\n![Bacillus anthracis colonies in Blood Agar - Bacilus anthraciscolonies inBlood Agarat 10x magnification.Photo credit: Todd Parker\u002FCDC.](https:\u002F\u002Fassets.microbeonline.com\u002Fblogs\u002FBacillus-anthracis-colonies-in-Blood-agar.jpg)Figure: *Bacillus anthracis* colonies in Blood Agar at 10x magnification. Photo credit: Todd Parker\u002FCDC.\n\n[Colony morphology](\u002Fcolony-morphology-bacteria-describe-bacterial-colonies\u002F) of *B. anthraci*s after 24 hours of incubation is as follows:\n\n#### Blood agar\n\n![Identification of Bacillus anthracis colony](https:\u002F\u002Fassets.microbeonline.com\u002Fblogs\u002Fanthrax-tetracore-for-Bacillus-anthracis.png)Figure: Identification of Bacillus anthracis colony\n\n*Bacillus anthracis* produces dry wrinkled, non-hemolytic colonies with frosted glass appearance after overnight incubation on sheep blood agar. Occasionally the colonies may have fringed edges or put out curled protrusions (tailing). This is the so-called **“Medusa head appearance”** but is not encountered as frequently as textbooks often suggest, and varies from batch-to-batch of media. Non-hemolytic Bacillus colonies can be presumptively identified using ‘**Red Line Alert Test**‘, which is an [immunochromatographic test](\u002Fimmunochromatography-principle-application\u002F) for the detection of surface protein found in *Bacillus anthracis* vegetative cells.\n\n> Medusa head appearance: When colonies are viewed under a low power microscope, the edge of the colony which is composed of long interlacing chains of bacilli, appears as locks of matted hair.\n\n#### Gelatin stab\n\nGrowth occurs as **inverted fir tree appearance** (due to liquefaction of gelatin which occurs maximum at the surface, and then slows down towards the bottom).\n\n![Fir tree appearance of Bacillus anthracis colonies  - Inverted fir tree appearance](https:\u002F\u002Fassets.microbeonline.com\u002Fblogs\u002Ffir-tree.png)Figure: Inverted fir tree appearance\n\n#### Selective media\n\n- **Solid medium with penicillin**: Colonies have a string of pearl appearance look (due to cells becoming larger and spherical because of their weaker cell walls under the action of penicillin, and cells tend to occur in a chain on the surface of agar).\n- **PLET medium**: It consists of polymyxin, lysozyme, EDTA and thallous acetate added in heart infusion agar. It has been devised to isolate *B. anthracis* from mixtures of other spore-bearing bacilli.\n\n**Gram staining** of the culture smear, reveals bamboo stick appearance, i.e. a long chain of gram-positive bacilli with non-bulging spores (appear as empty space).\n\n#### Serology\n\nAntibodies appear in convalescent sera and can be detected by ELISA or indirect hemagglutination methods.\n\n#### Molecular diagnosis\n\nPCR with specific primers can be used for further confirmation.\n\n#### References and further readings\n\n- *Anthrax| CDC*. (2019, February 19).\n- Information, N. C. for B., Pike, U. S. N. L. of M. 8600 R., MD, B., & Usa, 20894. (2008). [Laboratory procedures for diagnosis of anthrax, and isolation and identification of Bacillus anthracis. InAnthrax in Humans and Animals](https:\u002F\u002Fwww.ncbi.nlm.nih.gov\u002Fbooks\u002FNBK310485\u002F)*. 4th edition*. World Health Organization.\n- Procop, G. W., & Koneman, E. W. (2016). *Koneman’s Color Atlas and Textbook of Diagnostic Microbiology* (Seventh, International edition). Lippincott Williams and Wilkins.\n- Tille, P. (2017). *Bailey & Scott’s Diagnostic Microbiology* (14 edition). Mosby.",[],[46],"gram-positive-rods",[48,54,61,67,73,79,85,95],{"slug":49,"title":50,"description":50,"seoTitle":37,"seoDescription":37,"author":38,"createdDate":51,"lastUpdatedDate":40,"draft":41,"category":42,"image":37,"faq":52,"tags":53},"bacillus-cereus","Bacillus cereus: Morphology, Disease, Biochemical Tests","2021-05-31",[],[46],{"slug":55,"title":56,"description":56,"seoTitle":37,"seoDescription":37,"author":38,"createdDate":57,"lastUpdatedDate":40,"draft":41,"category":42,"image":37,"faq":58,"tags":59},"clostridium-perfringens-properties-diseases-and-diagnosis","Clostridium perfringens: Properties, Diseases, Diagnosis","2020-05-03",[],[46,60],"anaerobic-bacteriology",{"slug":62,"title":63,"description":63,"seoTitle":37,"seoDescription":37,"author":38,"createdDate":64,"lastUpdatedDate":40,"draft":41,"category":42,"image":37,"faq":65,"tags":66},"clostridium-tetani-properties-pathogenesis-diagnosis","Clostridium tetani: Properties, Pathogenesis, Lab Diagnosis","2020-05-02",[],[46,60],{"slug":68,"title":69,"description":69,"seoTitle":37,"seoDescription":37,"author":38,"createdDate":70,"lastUpdatedDate":40,"draft":41,"category":42,"image":37,"faq":71,"tags":72},"clostridium-botulinum-properties-pathogenesis-diagnosis","Clostridium botulinum: Properties, Pathogenesis, Lab Diagnosis","2020-05-01",[],[46],{"slug":74,"title":75,"description":75,"seoTitle":37,"seoDescription":37,"author":38,"createdDate":76,"lastUpdatedDate":40,"draft":41,"category":42,"image":37,"faq":77,"tags":78},"toxins-clostridium-perfringens-roles","Toxins of Clostridium perfringens and their roles","2020-04-06",[],[60,46],{"slug":80,"title":81,"description":81,"seoTitle":37,"seoDescription":37,"author":38,"createdDate":82,"lastUpdatedDate":40,"draft":41,"category":42,"image":37,"faq":83,"tags":84},"gram-positive-bacilli-rods-and-diseases","Gram-Positive Bacilli (Rods) and Diseases","2020-01-31",[],[46],{"slug":86,"title":87,"description":88,"seoTitle":37,"seoDescription":37,"author":38,"createdDate":89,"lastUpdatedDate":90,"draft":41,"category":91,"image":37,"faq":92,"tags":93},"robertsons-cooked-meat-medium-principle-composition-procedure-and-uses","Robertson's Cooked Meat (RCM) Medium: Principle, Composition, Uses, and Interpretation","Robertson's cooked meat medium cultivates and enriches anaerobes — especially Clostridium species — using meat particles as natural reducing agents. Learn the principle, preparation, how to interpret saccharolytic vs proteolytic reactions, and how it compares to thioglycollate broth.","2016-11-29","2026-07-06","culture-media",[],[60,46,94],"anaerobic-culture-techniques",{"slug":96,"title":97,"description":97,"seoTitle":37,"seoDescription":37,"author":38,"createdDate":98,"lastUpdatedDate":40,"draft":41,"category":42,"image":37,"faq":99,"tags":100},"clostridium-difficile-characteristics-disease-laboratory-diagnosis","Clostridioides difficile: Characteristics, Disease, Lab Diagnosis","2015-11-30",[],[46,60],[102,108,115,120,124,128,133,138,142,146],{"slug":103,"name":38,"description":104,"image":105,"body":106,"postCount":107},"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":109,"name":110,"description":111,"image":112,"body":113,"postCount":114},"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":116,"name":117,"description":118,"image":37,"body":37,"postCount":119},"sushmita-baniya","Sushmita Baniya","Author \u002F Contributor",32,{"slug":121,"name":122,"description":118,"image":37,"body":37,"postCount":123},"samikshya-acharya","Samikshya Acharya",20,{"slug":125,"name":126,"description":118,"image":37,"body":37,"postCount":127},"alisha-tripathi","Alisha Tripathi",6,{"slug":129,"name":130,"description":131,"image":37,"body":37,"postCount":132},"aastha-shrestha","Aastha Shrestha"," Author \u002F Contributor",10,{"slug":134,"name":135,"description":136,"image":37,"body":37,"postCount":137},"guest-author","Guest Author","Guest Author \u002F Contributor",2,{"slug":139,"name":140,"description":118,"image":37,"body":37,"postCount":141},"srijana-khanal","Srijana Khanal",18,{"slug":143,"name":144,"description":136,"image":37,"body":37,"postCount":145},"dr-poonam-acharya","Dr. Poonam Acharya",1,{"slug":147,"name":148,"description":118,"image":37,"body":149,"postCount":150},"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]