Mutations in L-Forms

CONVERSION of bacteria into L-forms involves changes in physiology as well as morphology. Comparing sensitivity to drugs of L-forms and bacteria, we are struck by the much higher resistance of the former to penicillin. Strains of L-forms of Proteus used in our laboratory are able to grow in the presence of 60,000 units penicillin/ml. On the other hand, they are more sensitive to streptomycin, chlortetracycline and chloramphenicol than are the bacterial forms. Tulasne and Minck 1 found that stable L-forms of P. morganii were 8,000 times and unstable L-forms of P. vulgaris were 25,000 times more sensitive than the corresponding bacterial forms. Lederberg and St. Clair 2 showed a fifty-fold decrease in resistance to streptomycin after converting Escherichia coli to the L-form. The authors suggest that “this can be viewed as the negation of the S R effect when the wall is stripped or a mutual reinforcement of penicillin and streptomycin in respect to another target”. They were inclined to accept the former interpretation. Horoszewicz and Horoszewicz 3 noted the inhibitory action of streptomycin on the conversion of P. mirabilis to the L-form. In the presence of the antibiotic it was necessary to inoculate 1,800 times more bacteria to obtain the same number of L-colonies.