[{"data":1,"prerenderedAt":-1},["ShallowReactive",2],{"$fxLN3MUwXCdr5RPjwZYIDpOj8CHyjOmngWTgoKXPtZbg":3,"$fX9aSzkivHdDBFkOAJRnv2bt97jT7f5JjNQwqPd9bvE0":32,"$f3Ft0rKFJHppdzE-vuveecxx1BUcg9iOlMLtyzf_MJDg":158},[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},"store-commercial-antimicrobial-discs","Transport and Storage of Antimicrobial Discs",null,"Acharya Tankeshwar","2013-08-26","2026-07-05",false,"bacteriology","Cartridges containing commercially prepared antimicrobial discs for susceptibility testing are generally packaged to ensure appropriate anhydrous conditions.\n\nTemperature and moisture are the most critical parameters affecting antimicrobial discs’ performance. Many antimicrobial agents are temperature sensitive, and moisture is a major cause of antibiotic degradation, so one should ensure careful handling of antimicrobial discs during transportation, storage, and regular usage.\n\n![](https:\u002F\u002Fassets.microbeonline.com\u002Fblogs\u002Fantimicrobial-disc-storage.jpg)## Transport\n\n1. Transport the discs in a cold chain. Do not accept antimicrobial discs from suppliers\u002Fvendors if it is not received in an ice pack.\n2. Up on the receipt of the discs, immediately store them at 2 to 8°**C. If you are not using them soon, store discs at  -20**°C.\n\n## Storage\n\n1. The antibiotic discs must be stored **according to the manufacturer’s instructions**, i.e., between -20°C and+ 8°C in a sealed, desiccated environment until needed.\n2. Sealed packages of disks that contain drugs from the [ß-lactam class](\u002Fbeta-lactam-antibiotics-mechanism-action-resistance\u002F) should be stored frozen, except for a small working supply, which may be refrigerated for at most one week.\n3. Some labile agents (e.g., imipenem, cefaclor, and clavulanic acid combinations) may retain excellent stability if stored frozen until the day of use.\n\n## Practice During Regular Usage\n\n1. Use only those discs that have not reached the manufacturer’s expiration date stated on the label. Discard the discs on the expiration date.\n2. Once a cartridge of discs has been removed from its sealed package, place it in a tightly sealed, desiccated container.\n3. Remove unopened disc containers from the refrigerator or [freezer](\u002Flaboratory-freezers-temperature-range-and-inventory-management\u002F) one to two hours before use.\n4. Allow unopened or used cartridges containing discs to **equilibrate to room temperature** before opening. This procedure minimizes the amount of condensation that occurs when warm air contacts cold disks.\n5. Even when the discs are removed, it should be made sure that they are not left out for too long.\n6. If a burner is used in your workplace, do not place antimicrobial discs around the vicinity of the burner.\n\n**Disc-dispensing apparatus**\n\n1. Disc-dispensing apparatus should be fitted with a tight cover and supplied with an adequate desiccant.\n2. Allow the dispenser to warm to room temperature before opening. *Excessive moisture should be avoided by replacing the desiccant when the indicator changes color.*\n3. Always refrigerate dispensing apparatus containing discs when not in use.\n\n**References**\n\n1. Balouiri, M., Sadiki, M., & Ibnsouda, S. K. (2016). Methods for *in vitro* evaluating antimicrobial activity: A review. *Journal of pharmaceutical analysis*, *6*(2), 71–79. \u003Chttps:\u002F\u002Fdoi.org\u002F10.1016\u002Fj.jpha.2015.11.005>\n2. CLSI: Performance Standards for Antimicrobial Susceptibility Testing.",[],[46],"antimicrobial-susceptibility-testing",[48,55,61,87,113,120,126,152],{"slug":49,"title":50,"description":50,"seoTitle":37,"seoDescription":37,"author":51,"createdDate":52,"lastUpdatedDate":40,"draft":41,"category":42,"image":37,"faq":53,"tags":54},"phenotypic-methods-for-the-detection-of-carbapenemases","Phenotypic Methods for the Detection of Carbapenemases","Nisha Rijal","2021-05-10",[],[46],{"slug":56,"title":57,"description":57,"seoTitle":37,"seoDescription":37,"author":51,"createdDate":58,"lastUpdatedDate":40,"draft":41,"category":42,"image":37,"faq":59,"tags":60},"carba-np-test-principle-procedure-results","Carba NP Test (CNPt): Principle, Procedure, Results","2021-02-04",[],[46],{"slug":62,"title":63,"description":64,"seoTitle":37,"seoDescription":37,"author":38,"createdDate":65,"lastUpdatedDate":66,"draft":41,"category":42,"image":37,"faq":67,"tags":86},"minimum-inhibitory-concentration-and-minimum-bactericidal-concentration-mbc","MIC vs MBC: What Each Measures and When the Difference Actually Matters","MIC stops bacterial growth; MBC kills it. Learn how MBC is determined from MIC tubes, the MBC\u002FMIC ratio, and the specific clinical scenarios (endocarditis, osteomyelitis, neutropenic sepsis) where the distinction changes treatment.","2020-03-30","2026-07-22",[68,71,74,77,80,83],{"question":69,"answer":70},"What is the difference between MIC and MBC?","MIC is the lowest antibiotic concentration that stops visible bacterial growth. MBC is the lowest concentration that kills ≥99.9% of the original bacterial population. MIC is a bacteriostatic endpoint; MBC is a bactericidal one.",{"question":72,"answer":73},"Is a lower MIC always better?","A lower MIC means the organism is more susceptible to that drug, but MIC alone doesn't predict cure — achievable drug concentration at the infection site and host immune status matter too.",{"question":75,"answer":76},"Why isn't MBC tested routinely in clinical labs?","Most infections are cleared by a combination of drug activity and host immune defenses, so a bacteriostatic effect (measured by MIC) is sufficient. MBC adds labor and turnaround time that's only justified in specific high-stakes infections.",{"question":78,"answer":79},"What does an MBC\u002FMIC ratio greater than 4 mean?","It indicates the drug is acting bacteriostatically rather than bactericidally against that specific organism.",{"question":81,"answer":82},"Can the same antibiotic be bactericidal against one organism and bacteriostatic against another?","Yes — bactericidal vs. bacteriostatic activity depends on the drug-organism combination, not the drug alone, which is exactly why MBC is tested rather than assumed from drug class.",{"question":84,"answer":85},"How is MBC determined from the MIC test?","A small volume from each clear (no-growth) MIC tube is subcultured onto antibiotic-free agar. The MBC is the lowest concentration whose subculture yields fewer than 0.1% of the original inoculum, equivalent to 99.9% killing.",[46],{"slug":88,"title":89,"description":90,"seoTitle":37,"seoDescription":37,"author":38,"createdDate":91,"lastUpdatedDate":92,"draft":41,"category":42,"image":37,"faq":93,"tags":112},"e-test-epsilometer-test-principle-purpose-procedure-results-and-interpretations","E-Test (Epsilometer): Why It Beats a Plain Disc Test, Procedure & Reading Rules","E-test gives an exact MIC value, not just a Susceptible\u002FResistant call. Full procedure, strip placement, and the reading rules that trip up most students — plus how E-test strips are used to screen for ESBL.","2015-01-09","2026-07-21",[94,97,100,103,106,109],{"question":95,"answer":96},"What's the difference between E-test and disc diffusion?","Disc diffusion gives only a category — Susceptible, Intermediate, or Resistant. E-test gives an exact MIC value in µg\u002FmL as well as the S\u002FI\u002FR category, which matters most for borderline or treatment-failure cases where the precise number changes the decision.",{"question":98,"answer":99},"Why does E-test use an exponential antibiotic gradient instead of a fixed concentration?","The continuous exponential gradient along the strip lets a single strip cover a wide range of concentrations, so the exact MIC can be read directly from where the inhibition ellipse intersects the scale, rather than testing one fixed concentration at a time.",{"question":101,"answer":102},"If the inhibition ellipse intersects at different points on either side of the strip, which value do you read?","Always read the greater (higher) value. This is a deliberately conservative rule — plates are never perfectly uniform, and erring toward the higher MIC avoids under-calling resistance.",{"question":104,"answer":105},"How is E-test used to screen for ESBL production?","Dual-ended combination strips carry the antibiotic alone on one end and the same antibiotic plus a β-lactamase inhibitor (such as clavulanic acid) on the other. A large drop in MIC on the inhibitor side compared to the antibiotic-alone side indicates ESBL production.",{"question":107,"answer":108},"Why is Mueller-Hinton agar used for E-test, and why does the depth matter?","Mueller-Hinton agar provides standardized, reproducible diffusion conditions with low inhibitor content. A uniform 4 mm depth is specified because agar depth directly affects how the antibiotic gradient diffuses, which affects the accuracy of the MIC reading.",{"question":110,"answer":111},"Is E-test used routinely on every isolate?","No — most labs reserve it for borderline, treatment-failure, or critical cases (such as confirming a borderline vancomycin MIC in MRSA) rather than running it as a routine first-line test, since disc diffusion is faster and cheaper for routine screening.",[46],{"slug":114,"title":115,"description":116,"seoTitle":37,"seoDescription":37,"author":38,"createdDate":117,"lastUpdatedDate":40,"draft":41,"category":42,"image":37,"faq":118,"tags":119},"modified-hodge-test-mht-carbapenemase-detection-principle-method-interpretations","Modified Hodge Test (MHT): Procedure, and Why CLSI No Longer Recommends It","MHT detects carbapenemase via a clover-leaf growth pattern, and CLSI dropped it from its guidelines in 2018 in favor of mCIM and Carba NP. The procedure, the limitations that led to its replacement, and where it's still used today.","2015-01-06",[],[46],{"slug":121,"title":122,"description":122,"seoTitle":37,"seoDescription":37,"author":38,"createdDate":123,"lastUpdatedDate":40,"draft":41,"category":42,"image":37,"faq":124,"tags":125},"stokes-disc-diffusion-method-principle-procedure-interpretation-results","Stokes Disc Diffusion Method: Principle, Procedure, Results","2014-12-28",[],[46],{"slug":127,"title":128,"description":129,"seoTitle":37,"seoDescription":37,"author":38,"createdDate":130,"lastUpdatedDate":131,"draft":41,"category":42,"image":37,"faq":132,"tags":151},"minimum-inhibitory-concentration-mic-broth-dilution-method-procedure-interpretation","Broth Dilution Method for MIC: Macrodilution vs Microdilution, Procedure & Troubleshooting","Step-by-step broth macrodilution and microdilution procedure for MIC determination — antibiotic stock prep, 0.5 McFarland standardization, reading results, and a troubleshooting guide for the errors that actually happen at the bench.","2013-11-15","2026-07-19",[133,136,139,142,145,148],{"question":134,"answer":135},"What's the difference between broth macrodilution and microdilution?","They follow the same principle — serial antibiotic dilutions inoculated with a standardized bacterial suspension — but macrodilution uses 1 mL per tube while microdilution uses 0.05–0.1 mL per well in a 96-well tray. Microdilution is far more common in routine clinical labs.",{"question":137,"answer":138},"Why must the inoculum be standardized to a 0.5 McFarland standard?","The MIC result depends directly on how many bacteria you start with. Too light an inoculum reads a falsely low MIC; too heavy reads a falsely high one. The 0.5 McFarland standard ensures every test starts from a comparable, known bacterial density.",{"question":140,"answer":141},"Why are reference strains like E. coli ATCC 25922 run alongside patient isolates?","They're quality-control checks. If a known reference strain's MIC falls outside its established CLSI range, it signals a problem with the test itself — inoculum, media, or technique — before patient results are trusted.",{"question":143,"answer":144},"What happens if microdilution trays are stacked too high during incubation?","Cultures at the center of a tall stack can incubate at a different temperature than intended, skewing growth and MIC readings — CLSI guidance caps stacking at four trays high.",{"question":146,"answer":147},"Can broth dilution MIC testing be automated?","Yes — systems like Vitek 2, MicroScan Walkaway, and BD Phoenix automate broth microdilution and reading, and are widely used in clinical labs alongside or instead of manual testing.",{"question":149,"answer":150},"Why might an MIC come back lower than clinically expected even with correct technique?","A few possibilities: the inoculum was too light, the cation-adjusted Mueller-Hinton broth's pH or calcium concentration is off, or there's a transcription\u002Freading error.",[46],{"slug":153,"title":154,"description":154,"seoTitle":37,"seoDescription":37,"author":38,"createdDate":155,"lastUpdatedDate":40,"draft":41,"category":42,"image":37,"faq":156,"tags":157},"basic-sets-drugs-used-routine-antimicrobial-susceptibility-testing-ast","Antimicrobial Susceptibility Testing (AST): Guidelines and Best Practices","2013-08-27",[],[46],[159,165,172,177,181,185,190,195,199,203],{"slug":160,"name":38,"description":161,"image":162,"body":163,"postCount":164},"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":166,"name":167,"description":168,"image":169,"body":170,"postCount":171},"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":173,"name":174,"description":175,"image":37,"body":37,"postCount":176},"sushmita-baniya","Sushmita Baniya","Author \u002F Contributor",32,{"slug":178,"name":179,"description":175,"image":37,"body":37,"postCount":180},"samikshya-acharya","Samikshya Acharya",20,{"slug":182,"name":183,"description":175,"image":37,"body":37,"postCount":184},"alisha-tripathi","Alisha Tripathi",6,{"slug":186,"name":187,"description":188,"image":37,"body":37,"postCount":189},"aastha-shrestha","Aastha Shrestha"," Author \u002F Contributor",10,{"slug":191,"name":192,"description":193,"image":37,"body":37,"postCount":194},"guest-author","Guest Author","Guest Author \u002F Contributor",2,{"slug":196,"name":197,"description":175,"image":37,"body":37,"postCount":198},"srijana-khanal","Srijana Khanal",18,{"slug":200,"name":201,"description":193,"image":37,"body":37,"postCount":202},"dr-poonam-acharya","Dr. Poonam Acharya",1,{"slug":204,"name":51,"description":175,"image":37,"body":205,"postCount":206},"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]