--- title: "Sabouraud’s Agar | Microbiology" description: "Sabouraud’s agar is an acidic fungal growth medium in Microbiology that suppresses bacteria and helps isolate dermatophytes from skin, hair, and nails." canonical: "https://fiveable.me/microbio/key-terms/sabourauds-agar" type: "key-term" subject: "Microbiology" unit: "Unit 5" --- # Sabouraud’s Agar | Microbiology ## Definition Sabouraud’s agar is a selective culture medium for fungi in Microbiology. Its acidic pH and nutrient mix favor fungal growth while discouraging many bacteria, especially in clinical samples. ## What It Is Sabouraud’s agar is a selective culture medium used in Microbiology to grow fungi, especially dermatophytes from skin, hair, and nail samples. If you are trying to isolate a fungus from a specimen that may also contain lots of bacteria, this is one of the standard media you would reach for. The formula is built to favor fungi in two main ways. First, it usually contains peptones and dextrose, which give the fungus a usable source of nitrogen and sugar. Second, it has a low pH, often around 5.6, which slows many bacteria more than it slows fungi. That simple shift in conditions makes the medium selective instead of just nutritive. The agar part is the solidifying agent. It does not feed the organism by itself, but it gives the culture a firm surface so fungal colonies can spread in a visible, organized way. That matters because fungal growth patterns, color, texture, and edge shape can be useful clues when you are identifying what grew. In practice, Sabouraud’s agar is often modified with antibiotics. Those additives cut down bacterial contamination even more, which is useful when the original sample comes from skin or nails where mixed microbes are common. Some versions may also be adjusted for specific fungi, but the basic idea stays the same: create a surface where fungi can outcompete unwanted bacteria. This medium shows up a lot in clinical microbiology because fungal infections can be slow-growing and easy to miss if bacteria take over the plate first. A sample from a scalp, foot lesion, or nail clipping can contain both the pathogen and a lot of normal flora. Sabouraud’s agar helps separate the signal from the noise so you can actually see the fungal isolate. If you are connecting it to the broader course, think of Sabouraud’s agar as a tool for selective cultivation, not a complete identification test. It gets the organism growing. After that, you would still use colony appearance, microscopy, and sometimes biochemical or molecular methods to identify the fungus more confidently. ## Why It Matters Sabouraud’s agar shows how microbiology uses environment to choose which microbes survive on a plate. Instead of assuming every organism will grow the same way, you adjust pH and nutrients so one group has the advantage. That idea comes up again and again in the course, whether you are thinking about selective media, clinical culturing, or how microbes compete in mixed samples. It also connects directly to fungal diagnosis. Dermatophytes can be slow growers, and if a plate is crowded with bacteria, the fungus may never be visible enough to study. Knowing why Sabouraud’s agar works helps you explain why a lab would use it for skin, hair, and nail specimens instead of a general-purpose medium. This term also reinforces a common lab skill: reading media by function. You are not just memorizing a name, you are learning to infer what the medium is designed to do from its ingredients and conditions. That kind of reasoning shows up in lab reports, image IDs, and questions about why one medium is chosen over another. ## Connections ### Dermatophytes Sabouraud’s agar is especially useful for isolating dermatophytes, the fungi that infect keratin-rich tissues like skin, hair, and nails. If you know what dermatophytes prefer to grow on, the choice of this medium makes more sense. In lab work, a suspected dermatophyte often starts as a slow-growing colony on Sabouraud’s agar before further testing confirms the species. ### Peptones Peptones are one of the nutrient ingredients in Sabouraud’s agar. They provide small peptide fragments and amino acids that fungi can use for growth. They matter because this medium is not selective just from acidity, it still has to feed the organism you want to culture. If the nutrient base were too weak, fungi might not grow well enough to detect or study. ### Agar Agar is the solidifying agent that turns Sabouraud’s agar into a plate you can streak or inoculate. It gives colonies a surface to spread on, which makes growth easier to observe and subculture. Agar itself is usually not the selective part of the medium, but without it you would not get the colony morphology that helps with fungal identification. ### [Mycobiont](/microbio/key-terms/mycobiont) A mycobiont is the fungal partner in a lichen, and that term connects to the course topic on lichens rather than to culture media directly. Sabouraud’s agar is about isolating free-living fungi in the lab, while a mycobiont is part of a symbiotic system in nature. Both remind you that fungi can appear in very different biological contexts. ## On the AP Exam A lab practical may show you a culture medium and ask you to identify why Sabouraud’s agar would be chosen for a sample from skin or nails. You would answer by linking the low pH and nutrient mix to fungal growth and bacterial suppression. A short-answer question may also ask you to compare it with a general-purpose medium and explain why a selective medium improves isolation. In image-based questions, the skill is often to recognize that the medium is being used to recover a fungus from a mixed specimen, not to name the species itself. ## Key Takeaways - Sabouraud’s agar is a selective medium designed to grow fungi, especially dermatophytes, while limiting many bacteria. - Its low pH is the main selective feature, and the peptones and dextrose provide nutrients for fungal growth. - Agar makes the medium solid, so you can observe colony appearance and work with isolated fungal growth. - Antibiotics are often added when the sample is likely to contain a lot of bacterial contamination. - In Microbiology, this medium is most useful for clinical specimens such as skin, hair, and nails. ## FAQs ### What is Sabouraud’s agar in Microbiology? Sabouraud’s agar is a selective culture medium used to grow fungi. Its acidic pH and nutrient composition favor fungal growth while discouraging many bacteria, which makes it useful for clinical specimens. ### Why does Sabouraud’s agar inhibit bacteria? The low pH slows many bacterial species more than it slows fungi. That creates a growth advantage for fungi, and the effect is often strengthened by antibiotics in some formulations. ### What specimens is Sabouraud’s agar used for? It is commonly used for skin scrapings, hair, and nail samples. Those specimens often contain mixed microbes, so a selective medium makes it easier to recover a fungal pathogen. ### Is Sabouraud’s agar the same as a general fungal medium? Not exactly. It is a fungal medium, but its main value is selectivity, not just nourishment. Compared with a more general culture plate, it is better when you need fungi to grow without being overrun by bacteria. ## Related Study Guides - [5.5 Lichens](/microbio/unit-5/5-lichens/study-guide/gKCHjV7PGHeTvXaD) ## About This Document Canonical Fiveable pages are available as Markdown at the same path plus `.md`. - [llms.txt](https://fiveable.me/llms.txt): index of Fiveable's sections and URL patterns - [llms-full.txt](https://fiveable.me/llms-full.txt): complete subject and unit listing - [MCP server](https://fiveable.me/mcp): call Fiveable as tools instead of fetching pages (`https://fiveable.me/api/mcp`) - [MCP server for AP teachers](https://fiveable.me/mcp/teachers): a teacher's classes, assignments and AP-rubric grading (`https://fiveable.me/api/mcp/teacher`) ## Structured Data ```json {"@context":"https://schema.org","@graph":[{"@type":"LearningResource","@id":"https://fiveable.me/microbio/key-terms/sabourauds-agar#resource","name":"Sabouraud’s Agar | Microbiology","url":"https://fiveable.me/microbio/key-terms/sabourauds-agar","learningResourceType":"Concept explainer","educationalLevel":"AP® / High School","about":{"@id":"https://fiveable.me/microbio/key-terms/sabourauds-agar#term"},"audience":{"@type":"EducationalAudience","educationalRole":"student"},"dateModified":"2026-07-03T02:23:51.977Z","isPartOf":{"@type":"Collection","name":"Microbiology Key Terms","url":"https://fiveable.me/microbio/key-terms"},"publisher":{"@type":"Organization","name":"Fiveable","url":"https://fiveable.me"}},{"@type":"DefinedTerm","@id":"https://fiveable.me/microbio/key-terms/sabourauds-agar#term","name":"Sabouraud’s agar","description":"Sabouraud’s agar is a selective culture medium for fungi in Microbiology. 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