[{"data":1,"prerenderedAt":-1},["ShallowReactive",2],{"$fxLN3MUwXCdr5RPjwZYIDpOj8CHyjOmngWTgoKXPtZbg":3,"$f4C_DsVf-cpTaYGEvMMJFatFQQUPxGAW8i-QS1Bbho5Y":32,"$f3Ft0rKFJHppdzE-vuveecxx1BUcg9iOlMLtyzf_MJDg":107},[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},"laboratory-diagnosis-of-syphilis","Laboratory Diagnosis of Syphilis",null,"Acharya Tankeshwar","2013-06-04","2026-07-21",false,"bacteriology","Syphilis is a sexually transmitted disease caused by the bacterium \\*Treponema pallidum.\\*Syphilis has diverse clinical manifestations and shares many clinical features with other treponemal and nontreponemal diseases (because of this, syphilis has been called “The Great Pretender”). The etiological agent, *Treponema pallidum*, **cannot be cultured,** and there is no single optimal alternative test.\n\nCommonly used laboratory diagnostic testing available for syphilis are:\n\n## Direct Diagnosis\n\nDirect laboratory methods for diagnosing syphilis include the detection of *Treponema pallidum* by microscopic examination of fluid or smears from lesions, histological examination of tissues, or nucleic acid amplification methods such as [polymerase chain reaction (PCR)](\u002Fpolymerase-chain-reaction-pcr-steps-types-applications\u002F)**.** Tests used for the direct detection of *Treponema pallidum* are;\n\n### Dark-field microscopy\n\n![Darkfield micrograph of Treponema pallidum - Darkfield micrograph ofTreponema pallidum(source: CDC)](https:\u002F\u002Fassets.microbeonline.com\u002Fblogs\u002FDarkfield-micrograph-of-Treponema-pallidum.jpg)Figure: Darkfield micrograph of *Treponema pallidum* (source: CDC)\n\nDark-field microscopy is used to demonstrate the presence of motile *Treponema pallidum* in lesions or aspirates in early-stage (primary or secondary) syphilis before healing lesions.\n\n### Direct fluorescent antibody test for *Treponema pallidum*\n\nIt is a diagnostic method used to detect the presence of *T. pallidum* in clinical specimens. This test relies on fluorescent-labeled antibodies that specifically bind to *T. pallidum* antigens. Here’s an overview of how the DFA test for *Treponema pallidum* is typically performed:\n\n## DFA Test Procedure for *T. pallidum*\n\n### 1. Specimen & Slide Preparation\n\n- **Specimen Collection:** Clinical specimens commonly collected for the DFA test include samples from syphilitic lesions, such as genital sores or mucous patches, as well as cerebrospinal fluid in cases of neurosyphilis.\n\n- **Slide Preparation:** A thin smear or impression of the specimen is prepared on a glass slide. The specimen is usually fixed to the slide to preserve the integrity of the *T. pallidum* cells.\n\n### 2. Staining Process\n\n- **Blocking Solution:** The slide is treated with a blocking solution to block non-specific binding of antibodies to the specimen.\n\n- **Fluorescent-Labeled Antibodies:** Fluorescent-labeled antibodies specific to *T. pallidum* antigens are applied to the slide. These antibodies are conjugated with a fluorescent dye, allowing for the visualization of the bacteria under a fluorescence microscope.\n\n- **Incubation:** The slide is incubated to allow the fluorescent antibodies to bind specifically to *T. pallidum* antigens in the specimen.\n\n- **Washing:** Unbound or non-specifically bound antibodies are washed away to reduce background fluorescence.\n\n### 3. Examination & Result\n\n- **Microscopic Examination:** A fluorescence microscope is used to examine the slide. When exposed to the appropriate wavelength of light, the bound fluorescent antibodies emit light, allowing for the visualization and identification of *T. pallidum*.\n\n- **Interpretation:** The presence of characteristic fluorescence in a spirochete-like pattern confirms the presence of *T. pallidum* in the specimen.\n\n## Molecular Methods for *Treponema pallidum* Detection\n\nNucleic acid amplification (PCR-based) and hybridization techniques offer excellent sensitivity and specificity for identifying *T. pallidum*, especially in early or primary stages where serology might lag.\n\n### 1. Polymerase Chain Reaction (PCR)\n\n- **Principle:** A widely used amplification technique targeting specific regions of *T. pallidum* genomic DNA.\n\n- **Procedure:**\n\n  1. **Collection:** A clinical specimen (such as a lesion swab or blood) is collected.\n\n  2. **Extraction:** *T. pallidum* DNA is isolated from the sample.\n\n  3. **Amplification:** Primers specific to *T. pallidum* DNA copy the target region.\n\n  4. **Detection:** The amplified DNA is visualized using gel electrophoresis, real-time PCR, or hybridization assays.\n\n### 2. Transcription-Mediated Amplification (TMA)\n\n- **Principle:** An isothermal (constant temperature) nucleic acid amplification technique designed to target and multiply RNA transcripts.\n\n- **Procedure:**\n\n  1. **Reverse Transcription:** *T. pallidum* RNA is copied into complementary DNA (cDNA).\n\n  2. **Amplification:** The cDNA is amplified isothermally via TMA.\n\n  3. **Detection:** The resulting RNA or cDNA is measured using specific detection probes.\n\n### 3. Loop-Mediated Isothermal Amplification (LAMP)\n\n- **Principle:** An isothermal amplification technique that rapidly copies DNA at a single, constant temperature using a specialized set of four to six distinct primers.\n\n- **Procedure:**\n\n  1. **Amplification:** *T. pallidum* DNA is amplified directly in a heating block without thermal cycling.\n\n  2. **Detection:** Results are read visually via turbidity (cloudiness), color change indicators, or fluorescence.\n\n### 4. Reverse Transcription-PCR (RT-PCR)\n\n- **Principle:** Combines reverse transcription of RNA into cDNA with standard PCR amplification to detect active gene transcription.\n\n- **Application:** Highly valuable for detecting *T. pallidum* RNA, particularly during the window of early syphilis.\n\n### 5. In Situ Hybridization (ISH)\n\n- **Principle:** Utilizes a labeled nucleic acid probe that binds directly to complementary *T. pallidum* DNA or RNA strands directly within intact tissue sections.\n\n- **Application:** Excellent for localizing and visualizing the spatial distribution of spirochetes directly within biopsy or clinical tissue specimens.\n\n## Indirect diagnosis\u002Fserological methods\n\nIt is based on serological tests for the detection of [antibodies](\u002Fimmunoglobulin-iga-structure-functions\u002F). Serological testing is the mainstay in the laboratory diagnosis and follow-up of syphilis. Serological tests fall into **two categories: nontreponemal tests for screening, and treponemal tests for confirmation.**\n\n### Nontreponemal tests\n\nThey measure both immunoglobulin ([IgG](\u002Figg-antibody-structure-subclasses-functions-and-clinical-significance\u002F) and [IgM](\u002Figm-antibody-structure-properties-functions-clinical-significance\u002F)) antiphospholipid antibodies formed by the host in response to lipoidal material released by damaged host cells early in infection and lipid from the cell surfaces of the treponeme itself.  Commonly used nontreponemal tests are\n\n#### Rapid plasma reagin (RPR) test\n\n#### Toluidine red unheated serum test (TRUST)\n\n#### Venereal Disease Research Laboratory (VDRL) test\n\n### Treponemal Tests\n\nAll **treponemal tests** use *Treponema pallidum* or its components as the antigen.\n\nTreponemal tests are used as confirmatory tests to verify reactivity in non-treponemal tests. Once positive, treponemal tests remain positive throughout life with or without treatment, so these tests can not be used to know the response to treatment.\n\nCommonly used treponemal tests are:\n\n#### Fluorescent treponemal antibody absorption test (FTA-ABS)test\n\n#### Treponema pallidum particle agglutination (TP-PA) test\n\n#### Treponema pallidum Hemagglutination Assay (TPHA)\n\n## Flow-chart for laboratory diagnosis of syphilis\n\nIf lesion exudate or tissue is available, a direct examination is performed, followed by a nontreponemal serology test. A treponemal test then confirms a reactive nontreponemal test.\n\nFigure: Testing algorithm for Primary Syphilis\n\nA confirmed serological test result indicates the presence of treponemal antibodies. Still, it does not indicate the stage of disease and, depending on the test, may not differentiate between past and current infections.\n\n**References**\n\n1. Madigan Michael T, Bender, Kelly S, Buckley, Daniel H, Sattley, W. Matthew, & Stahl, David A. (2018). [Brock Biology of Microorganisms](https:\u002F\u002Famzn.to\u002F2USOj0v) (15th Edition). Pearson.\n2. Meyer, J. Ch. (1996). Laboratory diagnosis of syphilis. *Sexually Transmitted Diseases: Advances in Diagnosis and Treatment*, 1–11. \u003Chttps:\u002F\u002Fdoi.org\u002F10.1159\u002F000424876>\n3. Larsen, S. A., Steiner, B. M., & Rudolph, A. H. (1995). Laboratory diagnosis and interpretation of tests for syphilis. *Clinical Microbiology Reviews*, *8*(1), 1–21. \u003Chttps:\u002F\u002Fdoi.org\u002F10.1128\u002Fcmr.8.1.1>",[],[46],"sexually-transmitted-infections-stis",[48,68],{"slug":49,"title":50,"description":51,"seoTitle":37,"seoDescription":37,"author":38,"createdDate":52,"lastUpdatedDate":40,"draft":41,"category":53,"image":37,"faq":54,"tags":67},"laboratory-diagnosis-trichomonas-vaginalis-infections","Trichomonas vaginalis: Clinical Features, Lab Diagnosis, and Differentiation from Bacterial Vaginosis","Trichomonas vaginalis vs Gardnerella vaginalis — how to tell trichomoniasis apart from bacterial vaginosis using pH, wet mount, whiff test, and clue cells. Complete lab diagnosis: microscopy, culture, NAAT.","2016-03-05","parasitology",[55,58,61,64],{"question":56,"answer":57},"How is Trichomonas vaginalis different from Gardnerella vaginalis \u002F bacterial vaginosis?","Trichomonas vaginalis is a flagellated protozoan parasite causing trichomoniasis, a true sexually transmitted infection diagnosed by finding motile trophozoites on microscopy. Bacterial vaginosis is not caused by a single organism but is a dysbiosis — a shift from normal Lactobacillus-dominant vaginal flora toward overgrowth of Gardnerella vaginalis and anaerobes. BV is diagnosed by finding clue cells or using the Amsel criteria\u002FNugent score, not by isolating Gardnerella alone, since it is present in low numbers in many healthy women. Trichomoniasis requires partner treatment; bacterial vaginosis does not.",{"question":59,"answer":60},"What is the best test to diagnose Trichomonas vaginalis infection?","Direct wet mount microscopy is the fastest initial test, looking for motile, pear-shaped trophozoites with characteristic jerky movement, but its sensitivity is moderate and depends on prompt specimen examination. Culture in Johnson’s and Trussell’s medium is highly sensitive (95%) and recommended when wet mount is negative. Nucleic acid amplification tests (NAAT), such as the Aptima Trichomonas vaginalis Assay, offer the highest sensitivity and are increasingly used, especially for testing asymptomatic men.",{"question":62,"answer":63},"Why does Trichomonas vaginalis need to be examined quickly after specimen collection?","Trichomonas vaginalis exists only as a trophozoite — it has no cyst stage. The trophozoite is fragile outside the host and loses motility relatively quickly, particularly with temperature changes. Since motility (the characteristic jerky movement) is the key diagnostic feature on wet mount, a delayed specimen can lead to a false-negative result simply because the organisms have stopped moving and become hard to distinguish from white blood cells of similar size.",{"question":65,"answer":66},"Should male partners of women with trichomoniasis be treated?","Yes. Most infected men are asymptomatic (only about 10% develop urethritis), but they remain infectious and are a common source of reinfection. Current STI management guidelines recommend treating sexual partners simultaneously with metronidazole, regardless of symptoms or testing status, to prevent treatment failure and ongoing transmission.",[46],{"slug":69,"title":70,"description":71,"seoTitle":37,"seoDescription":37,"author":38,"createdDate":72,"lastUpdatedDate":73,"draft":41,"category":74,"image":37,"faq":75,"tags":106},"hiv-structure-laboratory-diagnosis-and-natural-resistance","HIV: Structure, Laboratory Diagnosis, and Natural Resistance","Complete guide to HIV — structure (gp120, gp41, p24, reverse transcriptase), laboratory diagnosis (ELISA, Western blot, PCR, CD4 count), and why some people are naturally resistant to HIV infection (CCR5-delta32 mutation).","2026-06-16","2026-07-26","virology",[76,79,82,85,88,91,94,97,100,103],{"question":77,"answer":78},"What is the difference between HIV-1 and HIV-2?","HIV-1: global, more virulent, transmissible. HIV-2: West Africa, slower progression, lower viral loads, lower MTCT. NNRTIs ineffective against HIV-2. Differ primarily in gp120 structure.",{"question":80,"answer":81},"What is the HIV testing window period?","4th gen Ag\u002FAb combo: ~18-45 days. HIV RNA PCR: 10-14 days (shortest). Negative test during window does not exclude infection — retest at 45 and 90 days post-exposure.",{"question":83,"answer":84},"Why can't antibody tests diagnose HIV in newborns?","Maternal IgG crosses placenta, persisting up to 18 months. HIV PCR required for infants under 18 months — test at 14-21 days, 1-2 months, 4-6 months.",{"question":86,"answer":87},"What does the CCR5-delta32 mutation do?","32-bp deletion produces non-functional CCR5 not on cell surface. R5-tropic HIV cannot enter cells without CCR5. Homozygotes (~1% Western Europeans): broadly resistant. Heterozygotes: slower progression if infected.",{"question":89,"answer":90},"What is the difference between viral load and CD4 count?","CD4: measures immune damage sustained — guides OI prophylaxis timing. Viral load: measures active HIV replication — primary treatment response marker. Goal: undetectable viral load + rising CD4 count.",{"question":92,"answer":93},"What is the role of the Nef protein?","Decreases CD4 and MHC class I on infected cells, helping HIV evade immune detection. Some long-term non-progressors (LTNPs) carry HIV strains with Nef gene deletions that reduce replication fitness.",{"question":95,"answer":96},"How does HIV cause AIDS if the virus itself doesn't directly destroy most organs?","HIV progressively depletes CD4+ T lymphocytes, the cells that coordinate the adaptive immune response. Below a threshold of about 200 cells\u002FμL, the immune system can no longer control pathogens it normally handles easily, leading to opportunistic infections (fungal, parasitic, viral) that define AIDS. HIV causes immune collapse rather than direct organ damage.",{"question":98,"answer":99},"Why does it take years for HIV infection to progress to AIDS?","HIV replicates continuously from the point of infection, but the immune system initially partially controls it through CD8+ cytotoxic T cells. CD4+ T cells are destroyed at roughly 50–100 cells\u002FμL per year on average. It takes years of this slow attrition before the count drops to the AIDS-defining threshold.",{"question":101,"answer":102},"Why can't HIV be cured by stopping antiretroviral therapy once viral load is undetectable?","ART suppresses active viral replication but does not eliminate the integrated provirus from resting CD4+ T cells (the latent reservoir). When ART stops, viral replication rebounds from this reservoir within weeks. Eliminating the latent reservoir is the central challenge of HIV cure research.",{"question":104,"answer":105},"Why are babies born to HIV-positive mothers tested differently than adults?","Standard antibody tests detect maternal IgG, which crosses the placenta and persists in the infant for up to 18 months regardless of whether the infant is infected. HIV PCR (detecting viral RNA or proviral DNA) is the only reliable test for diagnosing HIV infection in infants under 18 months.",[46],[108,114,121,126,130,134,139,144,148,152],{"slug":109,"name":38,"description":110,"image":111,"body":112,"postCount":113},"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.*",434,{"slug":115,"name":116,"description":117,"image":118,"body":119,"postCount":120},"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":122,"name":123,"description":124,"image":37,"body":37,"postCount":125},"sushmita-baniya","Sushmita Baniya","Author \u002F Contributor",32,{"slug":127,"name":128,"description":124,"image":37,"body":37,"postCount":129},"samikshya-acharya","Samikshya Acharya",20,{"slug":131,"name":132,"description":124,"image":37,"body":37,"postCount":133},"alisha-tripathi","Alisha Tripathi",6,{"slug":135,"name":136,"description":137,"image":37,"body":37,"postCount":138},"aastha-shrestha","Aastha Shrestha"," Author \u002F Contributor",9,{"slug":140,"name":141,"description":142,"image":37,"body":37,"postCount":143},"guest-author","Guest Author","Guest Author \u002F Contributor",2,{"slug":145,"name":146,"description":124,"image":37,"body":37,"postCount":147},"srijana-khanal","Srijana Khanal",18,{"slug":149,"name":150,"description":142,"image":37,"body":37,"postCount":151},"dr-poonam-acharya","Dr. Poonam Acharya",1,{"slug":153,"name":154,"description":124,"image":37,"body":155,"postCount":156},"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]