[{"data":1,"prerenderedAt":-1},["ShallowReactive",2],{"$fxLN3MUwXCdr5RPjwZYIDpOj8CHyjOmngWTgoKXPtZbg":3,"$fcO2phK45S1Vm2iM-DO-LAdrEg5RUOd7Q0l9FJ45tJ0U":32,"$f3Ft0rKFJHppdzE-vuveecxx1BUcg9iOlMLtyzf_MJDg":63},[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":37,"seoTitle":38,"seoDescription":38,"author":39,"createdDate":40,"lastUpdatedDate":41,"draft":42,"category":43,"image":38,"body":44,"faq":45,"tags":61,"related":62},"nagler-reaction-lecithinsae-test-principle-procedure-results-limitations","Nagler's Reaction (Lecithinase Test): The Antitoxin Trick That Identifies Clostridium perfringens","Clostridium perfringens produces alpha-toxin, a lecithinase that clouds egg yolk agar with an opaque halo. The Nagler test proves it is the specific toxin by neutralizing it with antitoxin on half the plate. Here is the half-plate design, why the enzyme this test detects is the same one that destroys tissue in gas gangrene, and how lecithinase differs from lipase.",null,"Nisha Rijal","2015-09-01","2026-07-14",false,"biochemical-tests","## Why It Matters\n\nThe lecithinase this test detects is not a laboratory curiosity. It is the **alpha-toxin of *Clostridium perfringens***, the enzyme responsible for the catastrophic tissue destruction of **gas gangrene** (clostridial myonecrosis). The alpha-toxin is a phospholipase C: it hydrolyzes lecithin, a phospholipid in host cell membranes, lysing red cells, platelets, and muscle cells and spreading through tissue. So when the Nagler reaction shows an opaque halo that is *neutralized by antitoxin*, it is identifying the same enzyme that dissolves cell membranes in a limb infection.\n\nThat is the elegance of the Nagler test: it does not just detect lecithinase activity, it proves the activity is due to a *specific, antitoxin-neutralizable* toxin, which is what points to *C. perfringens* rather than the other lecithinase producers. The clinical stakes, gas gangrene is a surgical emergency, are why a rapid presumptive identification matters.\n\nLecithinase test or Nagler’s reaction is a biochemical test used to identify organisms that liberate phospholipases (lecithinases) e.g. [*Clostridium perfringens*](\u002Fclostridium-perfringens-properties-diseases-and-diagnosis\u002F). The alpha (α) toxin of *C. perfringens* has **phospholipase activity** and hence, helps in the differentiation of *C. perfringens* from other *Clostridium* spp that also produce lecithinase (*C. baratti, C. absonum, C. bifermantans, C. sordelli, and C. novyi*) by neutralization of its lecithinase C (phospholipase C) activity by an antitoxin\n\n![Nagler reaction - Lecithinase test or Nagler’s reaction](https:\u002F\u002Fassets.microbeonline.com\u002Fblogs\u002FNagleer-reaction-300x219.png)Figure: Lecithinase test or Nagler’s reaction\n\n*Bacillus cereus* also exhibits strong lecithinase activity but can be differentiated by its strong hemolytic property on sheep [blood agar](\u002Fblood-agar-composition-preparation-uses-and-types-of-hemolysis\u002F) and motility. Among Bacillus species, *B. thuringiensis* and *B. anthracis* are lecithinase positive or weakly positive. *B. anthracis, however,* is a nonmotile organism and produces nonhemolytic colonies.\n\n## Principle\n\nLecithin is a normal component of egg yolks. Bacterial lecithinase breaks down lecithin into phosphorylcholine and an insoluble diglyceride, which forms a precipitate in the medium. This precipitate appears as a white opaque halo surrounding the lecithinase-producing colony grown on the egg yolk agar medium.\n\nModified egg yolk agar is a differential and enriched medium used to isolate and differentiate different species based on their lecithinase and lipase production and proteolytic activity. The degradation of lecithin present in the egg yolk results in the formation of opaque precipitate around the colonies. The lipase enzyme hydrolyzes the fats within the egg yolk, which results in an iridescent sheen on the colony surface.\n\nNote the two egg-yolk-agar reactions are distinct and read differently: **lecithinase** produces an **opaque white halo** in the medium (this test), while **lipase** produces an **iridescent, oil-on-water sheen on the colony surface**. They detect different enzymes on different substrates. The lipase reaction is the basis of the separate **lipid hydrolysis (lipase) test** (usually on tributyrin agar, where a positive is a *clear* zone, the visual opposite of lecithinase's opaque halo). *C. perfringens* is the clean split: lecithinase-positive here, lipase-negative there. See the lipid hydrolysis test for that reaction's full method.\n\n## Requirements\n\n1. **Media**: Basal egg yolk media is prepared by dissolving the standard amount in distilled water, in which 10% of egg yolk is added after autoclaving and cooling the media before dispensing it into sterile Petri dishes. Various original modifications like modified egg yolk agar media, mannitol egg yolk media, etc., are also available and can be used for specified purposes.\n2. **Others:** Inoculating loop, spreader, pipettes\n3. **Equipment**: [Anaerobic gas pak](\u002Fgaspak-anaerobic-system\u002F) or candle jar or anaerobic incubator for anaerobic incubation\n\n## Quality control\n\nInspect egg yolk agar for freezing, contamination, cracks, and dehydration before storage and use. Discard the opaque media. Perform QC on each new lot of media before using them.\n\nFollowing strains can be used for quality control testing in naglers reaction\n\n- *Clostridium perfringens* ATCC 13124 –  Lecithinase positive\n- *Clostridium sporogenes* ATCC 11437 – Lecithinase negative\n- *Bacteroides fragilis* ATCC 25285 – No activity on agar\n\n## Procedure\n\nThe procedure of Nagler reaction is as follows:\n\n1. Label and dry an egg yolk media plate and mark the plate into two halves.\n2. Inoculate 60 µl of *Clostridium perfringens* type A antitoxin in half of the plate, spread over the agar surface using a spreader, and allow to absorb and dry.\n3. Mark the side of the plate in which the antitoxin is inoculated.\n4. Streak the test organism in a straight line from the toxin-free agar half of the plate to toxin containing side. Repeat the same procedure with control strains on the same plate.\n5. Incubate anaerobically at 35-37°C for 24-48 hrs.\n6. Examine the plate for an **opalescent halo around the inoculum and inhibition by antitoxin.**\n\n![Naglers test](https:\u002F\u002Fassets.microbeonline.com\u002Fblogs\u002FNaglers-reaction-of-Cl.-perfringens-1.jpg)Figure: Naglers test\n\n## Result and interpretation\n\n| Observance | Inference |\n| --- | --- |\n| A zone of opacity in the antitoxin-free half only but not on another half due to neutralization of the alpha-toxin. | Lecithinase positive |\n| A zone of opacity on both sides of the plate or no reaction on the agar. | Lecithinase negative |\n\n1. Catalase-positive, spore-forming, Gram-positive rods that are lecithinase positive, with large zones of opacity, belong to the *B. cereus*group. Lack of motility separates *B. anthracis*from the other members of the group.\n2. Lecithinase and lipase are useful as part of the identification of *Clostridium*to the species level.\n\n*C. perfringens* is lipase negative and lecithinase positive, which can be neutralized by adding anti-α-toxin prior to inoculation of the agar (the Nagler reaction). *C. sporogenes*is lipase positive. *C. difficile* is both lipase and lecithinase negative.\n\n1. A Gram-positive rod that is catalase-negative, hemolytic, and lecithinase positive is *A. haemolyticum*.\n2. Among the fluorescent group of non-glucose-fermenting, Gram-negative rods, *P. putida*is lecithinase negative and most *P. fluorescens* isolates are lecithinase positive. This test can substitute for [gelatin hydrolysis.](\u002Fgelatin-hydrolysis-test\u002F)\n3. [Burkholderia spp](\u002Fburkholderia-pseudomallei\u002F) are often lecithinase positive.\n\n## Limitations of the test\n\n- Maintenance of anaerobic conditions is compulsory.\n- A negative lecithinase test should be compared to an un-inoculated control plate, as lecithinase can diffuse throughout the entire agar plate and make interpretation difficult.\n- *C. perfringens* type A antitoxin is not specific for *C. perfringens*; a positive Nagler reaction can also be produced by *C. bifermentans , C. sordelli* , and *C. baratti* if heavy inoculum is used.\n- Non-glucose fermenting rods may give small zones of opacity.\n\n## Egg Yolk Agar Medium Composition\n\nMcClung and Toabe agar, modified for lecithinase and lipase tests\n\n| Ingredients | Gram\u002FLiter |\n| --- | --- |\n| Proteose no. 2 peptone or Polypeptone (BBL) | 40.0 g |\n| Disodium phosphate | 5.0 g |\n| Monopotassium phosphate | 1.0 g |\n| Sodium chloride | 2.0 g |\n| Magnesium sulfate | 0.1 g |\n| Glucose | 2 g |\n| Hemin solution, 5 mg\u002Fml | 1.0 ml |\n| Agar | 20.0 g |\n| Water | 1.0 liter |\n\n## Preparation\n\n1. Suspend ingredients, and adjust the pH to 7.6.\n2. Mix, and boil to dissolve.\n3. Dispense 20 ml per tube, and autoclave at 118°C for 15 min.\n4. Cool to 50°C, and to each tube, add 2 ml of commercial egg yolk emulsion or 1 ml of egg yolk emulsion prepared as follows:  Scrub, and then soak, an antimicrobial-agent-free hen egg in 95% ethanol for 1 h. Aseptically aspirate or separate the egg yolk. Add equal volumes of egg yolk to sterile saline, and stir to make a smooth suspension.\n5. Mix, and pour into plates.\n\n**References and further readings**\n\n1. Leber AL, editor. *Clinical Microbiology Procedures Handbook.* 4th ed. Washington, DC: ASM Press; 2016. doi:10.1128\u002F9781555818814\n2. Procop GW, Church DL, Hall GS, Janda WM, Koneman EW, Schreckenberger PC, Woods GL. *Koneman's Color Atlas and Textbook of Diagnostic Microbiology.* 7th ed. Philadelphia: Wolters Kluwer; 2017.\n3. Jousimies-Somer H, Summanen P, Citron DM, et al. *Wadsworth-KTL Anaerobic Bacteriology Manual.* 6th ed. Belmont, CA: Star Publishing; 2002.\n4. Tille PM. *Bailey and Scott's Diagnostic Microbiology.* 15th ed. St. Louis: Elsevier; 2022.",[46,49,52,55,58],{"question":47,"answer":48},"What is the Nagler reaction and what does it identify?","The Nagler reaction is a test that identifies Clostridium perfringens by detecting its alpha-toxin, a lecithinase (phospholipase C). On egg yolk agar, the lecithinase breaks down lecithin into an insoluble diglyceride that forms an opaque white halo around the growth. The test is made specific by applying C. perfringens type A antitoxin to half the plate: a true positive shows the opaque halo on the antitoxin-free half but not on the antitoxin half, because the antitoxin neutralizes the toxin. This proves the lecithinase is the neutralizable alpha-toxin, pointing to the C. perfringens group.",{"question":50,"answer":51},"How is the lecithinase (Nagler) test different from the lipase test?","They detect different enzymes and give opposite-looking results. Lecithinase acts on lecithin (a phospholipid) and produces an opaque white halo in egg yolk agar. Lipase acts on triglycerides and produces either an iridescent sheen on the colony surface (on egg yolk agar) or a clear zone (on tributyrin agar). C. perfringens is the clean contrast: lecithinase-positive but lipase-negative, while C. sporogenes is lipase-positive. So lecithinase clouds the medium and lipase clears it.",{"question":53,"answer":54},"Why is antitoxin used in the Nagler test?","To make the test specific for the C. perfringens alpha-toxin. Many organisms produce a lecithinase, so an opaque halo alone is not enough to identify C. perfringens. By applying C. perfringens type A antitoxin to half the plate, the test shows whether the lecithinase is the specific, neutralizable alpha-toxin: if the halo is inhibited on the antitoxin side but present on the antitoxin-free side, the reaction is a positive Nagler test. A halo on both sides means the lecithinase is not neutralizable alpha-toxin, so the test is negative.",{"question":56,"answer":57},"Is a positive Nagler reaction specific for Clostridium perfringens?","It is presumptive for the C. perfringens group rather than absolutely specific. The type A antitoxin can cross-neutralize the lecithinases of C. bifermentans, C. sordellii, and C. baratii, especially with a heavy inoculum, so these can also give a positive Nagler reaction. Definitive identification requires additional biochemical, immunological, or molecular testing. Clinically, though, a positive Nagler reaction on a suspicious wound isolate is a strong and rapid presumptive pointer to C. perfringens.",{"question":59,"answer":60},"Why does the Nagler test matter clinically?","Because the lecithinase it detects is the C. perfringens alpha-toxin, the enzyme responsible for the tissue destruction of gas gangrene (clostridial myonecrosis). The alpha-toxin is a phospholipase C that hydrolyzes membrane phospholipids, lysing red cells, platelets, and muscle cells and spreading through tissue. Gas gangrene is a surgical emergency, so a rapid presumptive identification of C. perfringens is clinically valuable, and the Nagler test provides one by detecting the toxin itself.",[],[],[64,71,78,83,87,91,96,101,105,109],{"slug":65,"name":66,"description":67,"image":68,"body":69,"postCount":70},"acharya-tankeshwar","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":72,"name":73,"description":74,"image":75,"body":76,"postCount":77},"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":79,"name":80,"description":81,"image":38,"body":38,"postCount":82},"sushmita-baniya","Sushmita Baniya","Author \u002F Contributor",32,{"slug":84,"name":85,"description":81,"image":38,"body":38,"postCount":86},"samikshya-acharya","Samikshya Acharya",20,{"slug":88,"name":89,"description":81,"image":38,"body":38,"postCount":90},"alisha-tripathi","Alisha Tripathi",6,{"slug":92,"name":93,"description":94,"image":38,"body":38,"postCount":95},"aastha-shrestha","Aastha Shrestha"," Author \u002F Contributor",10,{"slug":97,"name":98,"description":99,"image":38,"body":38,"postCount":100},"guest-author","Guest Author","Guest Author \u002F Contributor",2,{"slug":102,"name":103,"description":81,"image":38,"body":38,"postCount":104},"srijana-khanal","Srijana Khanal",18,{"slug":106,"name":107,"description":99,"image":38,"body":38,"postCount":108},"dr-poonam-acharya","Dr. Poonam Acharya",1,{"slug":110,"name":39,"description":81,"image":38,"body":111,"postCount":112},"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]