How does a stained smear of S epi and E coli made from 7-day-old cultures would appear?

If a stained smear of Staphylococcus epidermidis and Escherichia coli made from 7-day-old cultures were examined under a microscope, it would exhibit various characteristics based on the specific staining method used. Let's consider Gram staining, a widely used differential staining technique in microbiology:

Gram Staining Results:

1). Staphylococcus epidermidis:

- Gram-positive: S. epidermidis would retain the crystal violet dye and appear purple under the microscope. Gram-positive bacteria possess a thick layer of peptidoglycan in their cell walls, enabling them to retain the initial stain during the decolorization step.

2). Escherichia coli:

- Gram-negative: E. coli would lose the crystal violet dye during the decolorization step and subsequently take up the counterstain (safranin or fuchsin). It would appear red or pink under the microscope. Gram-negative bacteria have a relatively thin peptidoglycan layer and an outer membrane, making them Gram-negative.

Additional Observations:

- Cellular Morphology:

- S. epidermidis: It forms grape-like clusters of round or oval-shaped cells.

- E. coli: Rod-shaped, single cells typically arranged in short chains or pairs.

- Colony Characteristics:

- S. epidermidis: May exhibit white or gray-white, circular colonies on agar plates.

- E. coli: Typically has pink or reddish colonies on agar plates due to its ability to ferment lactose.

- Pigmentation:

- S. epidermidis: Produces no pigments and appears non-pigmented.

- E. coli: Some strains may produce pigments, such as a bluish-green pigment called "colicin."

However, it's important to note that some bacterial strains may exhibit variations in their staining properties or colony characteristics. Always refer to standard diagnostic tests and biochemical assays for accurate identification and differentiation of bacterial species.