Gramicidin is a mixture of three antibacterial polypeptides that work together to form a channel that spans cell membranes. As evidenced by these micrographs, oblique illumination adds a pseudo three-dimensional effect to images when compared to unaided brightfield microscopy.

The antibiotic increases the permeability of the bacterial cell membrane to inorganic cations by forming a network of channels through the normal lipid bilayer of the membrane. Medicinally, gramicidin is often used in a combination with other drugs for treating inflammation of the skin, eyes, and ears. Side effects include local irritation of areas with the applied drug.

Transmitted oblique illumination was obtained with a Hoffman-style substage condenser fitted with an offset aperture slit, which provides illumination from an oblique angle with respect to the optical axis of the QX3 microscope. Digital images were recorded with the QX3 interactive software operating from the Live View menu. In the case of birefringent specimens, a polarizer was added beneath the Hoffman condenser and an analyzer was placed in front of the QX3 lens cover. In some instances, a full-wave retardation plate was inserted between the specimen and the analyzer before capturing images.

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