Evaluation of various antibiotics for induction of L forms from Staphylococcus aureus strains isolated from bovine mastitis.

Forty-five strains of Staphylococcus aureus were treated with 11 antibiotics and tested for induction to L forms. Thirty-seven strains were induced to L forms with at least one antibiotic, while eight strains produced no L forms under the conditions used. L forms were induced only with beta-lactam antibiotics and with a combination of penicillin and streptomycin. Novobiocin induced no true L forms but induced intermediate forms from seven strains. Strains resistant to penicillin yielded L forms only with beta-lactam antibiotics active against penicillin-resistant organisms. Strains failing to yield L forms were susceptible to the antibiotics used, and resistance appeared to play no role in the induction of L forms with these strains.