Genetic transformation of rifampicin resistance in Lactobacillus acidophilus.

Lactobacillus acidophilus strain 100-33, originally isolated from swine faeces, was transformed to rifampicin resistance with DNA from spontaneous rifampicin-resistant mutants derived from it. Cells of the recipient strain were treated with lysozyme and mutanolysin, mixed with donor DNA and polyethylene glycol and grown on a regeneration medium overnight. After 48 h incubation, the numbers of rifampicin-resistant cells in the populations of regenerated cells were estimated from numbers of colonies. Efficiency of the lysozyme/mutanolysin treatment (the ratio of the number of osmotically fragile cells after the enzyme treatment to the initial cell number) was about 99%. The regeneration frequency of the enzyme-treated cells varied from 5 to 67%. The transformation frequency varied from about 0.2 X 10(-8) to 8.0 X 10(-8) transformants per regenerated cell per microgram DNA. To our knowledge, this method for genetic transformation is the first to be reported for a Lactobacillus strain.