Often, cultures that are very old will stain Gram negative even if they're normally Gram positive....

Often, cultures that are very old will stain Gram negative even if they're normally Gram positive. Offer an explanation for this by considering how the status of the cell wall might affect Gram staining. Considering you can’t identify bacteria from a gram stain, why might a physician perform a gram stain on a sample before prescribing an antibiotic?

Expert Solution

1. Young cultures are required to perform Gram staining accurately as cell wall thins, loses its strength, and becomes damaged in old cultures and therefore will not be able to retain the primary stain. Gram staining works best when the cells are in the exponential phase of growth with proper cell walls. Older cultures have more ruptured and dead cells with broken cell walls, which may not be able to retain the crystal violet - iodine complex.

2. Doctors perform a gram stain on a sample before prescribing an antibiotic as antibiotic sensitivity is highly correlated to the type of cell wall. Anionic glycopolymers called wall teichoic acids seen in in Gram positive bacteria are important mediators of antibiotic resistance. They are found to involve in the initial steps of transformation, which is an important mechanism of horizontal gene transfer that causes antibiotic resistance in many bacteria.

gladiator answered 2 years ago

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