Gram stain
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Gram stain is a method of staining used to classify bacterial species into two large groups: gram-positive bacteria and gram-negative bacteria. It may also be used to diagnose a fungal infection. The
A Gram stain of mixed Staphylococcus aureus (S. aureus ATCC 25923, gram-positive cocci, in purple) and Escherichia coli (E. coli ATCC 11775, gram-negative bacilli, in red), the most common Gram stain reference bacteria
Gram stain of Candida albicans from a vaginal swab. The small oval chlamydospores are 2–4 μm in diameter.
Purple-stained gram-positive (left) and pink-stained gram-negative (right)
Gram-stain of gram-positive streptococci surrounded by pus cells
Counterstain
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A counterstain is a stain with colour contrasting to the principal stain, making the stained structure easily visible using a microscope.
Gram-positive anthrax bacteria with counterstained white blood cells