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J Bacteriol. 1968 August; 96(2): 352-357
Copyright © 1968 American Society for Microbiology. All Rights Reserved.

Listeria monocytogenes L Forms I. Induction, Maintenance, and Biological Characteristics¹

Department of Bacteriology and Public Health, Washington State University, Pullman, Washington 99163
Division of Microbiology, Scripps Clinic, La Jolla, California 92038

ABSTRACT

L forms were induced from 15 of 16 strains of Listeria monocytogenes on penicillin gradient plates incubated under aerobic conditions. The culture medium for maintenance of these L forms must contain an electrolyte in a concentration of 1% or sucrose in a concentration of 10%. The electrolytes NaCl, KCl, or MgSO₄ were used in both induction and maintenance media. Induction of L forms occurred more rapidly on media containing KCl. Listeria L forms had the same fermentation reactions as the parent bacterium. The L-form growth in liquid medium was slow, not extensive, and appeared as clumps on the bottom of culture tubes. The morphology of Listeria L forms was similar to that reported for other bacterial L forms. The L forms derived from strain 10403, serotype 1, were stable after two or more passages on penicillin media. They did not revert to the bacterial form after 40 subcultures on penicillin-free media. Some L-form colonies derived from strain 10403 did revert to the bacterial form when transferred directly from induction plates to penicillin-free media. Studies of the growth characteristics for L forms derived from strain 10403 gave the following results: an optimal temperature of 30 C, high electrolyte or sucrose concentration necessary for induction and maintenance, and no requirement for serum.

¹ Presented in part at the annual meeting of the Northwest Branch of the American Society for Microbiology, University of Washington, Seattle, 8–9 September 1967. These studies were conducted by the senior author in partial fulfillment of the requirements for the M.S. degree in the Department of Bacteriology and Public Health, Washington State University, Pullman.

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