What is the meaning of passage in microbial culture handling and how many passages are acceptable as per pharmacopoeia?

Subculturing is one of the method to transfer and preserve the microbial culture for long time. But how many transfers are acceptable, this is a question of importance and what happens if we exceed the recommended number of transfers? First we have to understand the meaning of passage. Passage is define as the transfer of microorganisms from viable culture to fresh medium. Every transfer is called passage whether we transfer the culture from solid media to solid media or solid media to liquid media. As per pharmacopoeia, the microorganisms involved in the test should not be five passage removed from the orignal culture which means we can only transfer the culture up to five times into fresh medium from the orignal culture. Next question comes why not more than five passages? If we go for more than five passages, there might be chances of phenotypic changes or mutation in the culture. To prevent such type mutation not more than five passages are recommended.

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