Under what conditions gram negative bacteria turns to gram posetive?

Usually gram negative bacteria willl always stain Gram negative. The property of the Gram Negative bacterai that makes them stain Gram negative is their thin cell wall (which is composed of peptidoglycan).





I believe what you intend to ask is under what conditions willl a Gram Positive bacteria turn into a Gram Negative bacteria.


The reason that Gram Positive bacteria stain gram positive is becuase their thick peptidoglycan cell wall retains a purple stain in the gram staining process. When Gram positive bacteria are grwon in a single culture, such as a test tube, for a long period of time without adding any additional nutrients to the broth then the broth will have a low nutrient concentration. When there is a low amount of nutirents present then the Gram positive bacteria will only make a thin cell wall. By making a thin cell wall the gram positive bacteria will not retain the purple stain and will stain gram negative.





Just remember that the bacteria is still Gram positive but just composes a thin cell wall that makes it stain gram negative. It is for this reason that it is suggested to only Gram stain a fresh bacterial culture as this will usually prevent a false gram negative stain