This study investigates intergeneric transformation between Staphylococcus aureus (DNA donors) and Streptococcus strain CHALLIS (recipient), addressing previous controversies about whether such genetic exchange occurs. The researchers isolated DNA from 21 staphylococcal strains using various methods, obtaining 126 total preparations. Only 8 preparations from 4 S. aureus strains successfully transferred the streptomycin-resistance marker to CHALLIS, with yields of 0.001-0.017% relative to homospecific (same-species) transformation. Notably, no other antibiotic-resistance markers (penicillin, novobiocin, erythromycin, oxytetracycline) could be transferred. The staphylococcal strains yielding active DNA had GC content of 32.7-37.6%, about 5-9% lower than CHALLIS (41.8%). DNA re-isolated from CHALLIS transformants showed high homospecific transformation yields, indicating the foreign marker integrated successfully into the recipient chromosome. The extreme difficulty in obtaining active staphylococcal DNA preparations, likely due to nuclease activity, and limited marker transfer prevented using this system as a practical genetic tool for studying staphylococcal antibiotic resistance.

Key findings

• Intergeneric transformation from Staphylococcus aureus to Streptococcus CHALLIS is confirmed but extremely rare (0.001-0.017% yield relative to homospecific transformation)
• Only the streptomycin-resistance marker transferred successfully; penicillin, novobiocin, erythromycin, and oxytetracycline resistance markers could not be transferred
• Staphylococcal DNA preparation difficulty stems from nuclease activity; none of the tested isolation methods (Pakula & Tyc, Catlin & Cunningham, Marmur, Blobel) reliably produced active DNA
• The staphylococcal marker integrated fully into the CHALLIS chromosome, as evidenced by high homospecific transformation yields from re-isolated DNA
• Successful donor strains had GC content 4.9-9% lower than recipient CHALLIS, demonstrating transformation can occur despite substantial DNA composition differences