Sabouraud agar is a selective medium that is formulated to allow growth of fungi and inhibit the growth of bacteria. The available means of inhibiting bacterial growth in Sabouraud’s pre-antibiotic era was an acidic medium (pH 5.6). However, the addition of antibiotics to the acidic medium to inhibit bacteria (and sometimes saprophytic fungi, depending on the particular antibiotics used) is common in currently used versions. Glucose is present at the high level of 4% in Sabouraud’s formulation to assist in vigorous fermentation and subsequent acid production by any bacteria present. High acid concentrations eventually serve to inhibit all bacterial growth.
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