A smear from a sputum specimen is fixed to a glass slide, flooded with carbol fuchsin, heated, decolorized with acid-alcohol, and counterstained with methylene blue. If acid-fast bacilli are present, they retain the red stain against a blue background and a patient with suspected tuberculosis is now one step closer to a confirmed diagnosis.
Staining techniques transform invisible microorganisms into visible, interpretable findings. They are among the oldest tools in diagnostic microbiology and remain essential in every clinical laboratory, including in resource-limited settings where molecular testing is unavailable.
This section covers all major staining methods in clinical and research microbiology:
Each article covers the chemical principle behind the stain, the step-by-step procedure, how to interpret the result, what a false-positive or false-negative looks like, and how this stain fits into the diagnostic algorithm for the relevant organisms.
Calcofluor white binds chitin in fungal cell walls, producing bright fluorescence under UV light. Learn the principle, KOH-CFW combined method, specimen-specific applications, and how to interpret results for fungi, Pneumocystis, and Acanthamoeba.
PAS staining detects fungi in tissue biopsies, diagnoses Whipple's disease, and identifies glycogen storage disorders. Learn the principle, procedure, results, and clinical applica...
Complete Giemsa staining guide; stock and working solution preparation, pH 7.2 buffer chemistry, thick/thin smear procedure, organism-specific results, and a troubleshooting table...
Step-by-step preparation of crystal violet, Gram's iodine, decoloriser, and safranin — with storage conditions, shelf life, and QC checks to ensure reliable Gram staining results.
Capsule staining detects bacterial capsules — a key virulence factor. Learn the India ink and Anthony's methods, clinically important capsulated organisms, and the Quellung reactio...
Simple staining uses a single basic dye to reveal bacterial cell morphology, size, and arrangement. Learn the methylene blue procedure, when simple staining is used over Gram stain...
Acridine orange is a fluorescent dye that detects bacteria in blood cultures, mycobacteria, fungi, and malaria parasites. Learn the principle, procedure, results interpretation, an...
Albert stain detects metachromatic (volutin) granules in Corynebacterium diphtheriae, a key presumptive identification test for diphtheria. Learn the two-reagent principle, step-by...
Endospore staining detects heat-resistant bacterial spores in Bacillus and Clostridium species. Learn the Schaeffer-Fulton method, Dorner's method, spore position interpretation, a...
Auramine-rhodamine is a WHO-recommended fluorochrome stain for detecting acid-fast bacilli, which is more sensitive than Ziehl-Neelsen and faster to screen. Learn the Truant method...
Master gram staining: step-by-step procedure, results interpretation, clinical significance of each gram stain pattern, organism-specific appearances, quality control, and troubles...
LPCB is the standard mounting medium for microscopic fungal identification — staining chitin in cell walls to reveal hyphae, conidia, and spore arrangements. Learn the tease mount...
Toluidine blue stains metachromatic granules in C. diphtheriae, Pneumocystis jirovecii cysts in BAL specimens, and H. pylori in gastric biopsies. Learn the procedure, uses, and int...
Flagella staining reveals the number and arrangement of bacterial flagella — key features for species identification. Learn the Ryu wet-mount method, flagellar arrangement types wi...
The hot ZN acid-fast staining method step by step, why mycolic acid holds carbol fuchsin against acid-alcohol, WHO smear grading from scanty to 3+, and what a negative smear does a...
