Inactivation of the SauI type I restriction-modification system is not sufficient to generate Staphylococcus aureus strains capable of efficiently accepting foreign DNA.

Genetic manipulation of Staphylococcus aureus is limited by the availability of only a single strain, RN4220, that is capable of easily accepting foreign DNA. Inactivation of the hsdR gene of the SauI type I restriction-modification system was shown previously to be responsible for the high transformation efficiency of RN4220 (D. E. Waldron and J. A. Lindsay, J Bacteriol. 188:5578-5585, 2006). However, deletion of this gene in three different S. aureus strains was not sufficient to make them readily transformable, which would be remarkably useful for genetic studies of this pathogenic organism. These results indicate that another unknown factor(s) is required for the transformable phenotype in S. aureus.