Use of phage lambda CI857AprTcrN derivative for isolation of prophage-free cells.

A method for obtaining nonlysogenic bacteria from wild-type phage lysogenized strains using phage lambda with AprTcr markers and double amber-mutation in N gene is proposed. When the lysogenic culture is infected with antibiotic-resistant phage, the nonlysogenic cells present in the population are lysogenized and isolated on selective medium with Ap and Tc. Subsequent culturing of lysogenized cells on media without antibiotics leads to phage elimination due to its instability.