L-form induction, morphology, and development in two related strains of Erysipelothrix rhusiopathiae

Two related strains of Erysipelothrix rhusiopathiae, one the parent and the other an L-form revertant, were studied for their propensity or ability to produce L-forms under the influence of penicillin. The parent strain produced L-forms in nutrient solid media in an osmolarity range between 0.85 and 5.0% NaCl concentration whereas the revertant strain did so between 0.5 and 3.0% NaCl concentration. When various hyperosmolar media were tried without penicillin, recovery of L-forms from the revertant strain was optimal at a salt concentration of 2.0%, whereas the parent strain occasionally produced a few L-forms on 3.0% salt medium only. The process of penicillin-induced transformation from bacteria to L-form followed an unusual morphological sequence, beginning with beading of the bacterial body, followed by disintegration into granules from which the L-form colony derived. No large bodies were seen during the initial process of L-form induction, but they evolved later from the original granules and had the potential to reproduce L-type growth. The spontaneous development of L-forms in hyperosmolar media had a different morphological sequence starting with elongation of the bacteria into filaments which later developed polar and central dilatations from which granules and L-type growth developed. The differences in biological behavior between these related bacterial strains suggest that the revertant strain developed new properties, probably of genetic origin. Consequently, the assumption that L-forms revert to the "parent" bacteria may not always be justified. It can be made only after the biological properties of the parent and the revertant organisms have been properly identified.