The Significance of Pleomorphism in Bacteroides Strains

Abstract

During the last 4 yrs., 23 Bacteroides strains have been isolated in our laboratory from pathological specimens. Nine presented a characteristic pleomorphism, consisting in the swelling of the bacteria into large round or fusiform bodies. Three of these pleomorphic strains produced the L type of colonies and in 4 the reproduction of bacteria from the large bodies was observed. One strain (132) was especially appropriate for the study of the development and transformation of the large bodies. The cultures on solid media consisted of regular-shaped small bacteria which swelled up in broth, almost without exception, into large bodies. Re-transferred to agar, these were viable and developed either into L type or bacterial colonies. This development was observed in slide cultures under the microscope. The L type of colonies developed by germination of small granules in one or several directions from the large body. The bacteria were reproduced essentially by segmentation of the large bodies, which often increased in size and were distorted by the growth process. At the time the large bodies developed, the bacteria contained granules giving chromatin-staining with Giemsa soln. The young large bodies contained 4 or 5 such granules. As the bodies enlarged, the number of granules increased. The segmentation of the large bodies seemed to proceed around these granules and the L type of growth seemed to grow out directly from these granules. The L colonies isolated from strain 132 grew without difficulty in pure culture on appropriate media. Both the young and well-developed L-type colonies were similar in appearance to the L1 isolated from Streptobacillus moniliformis, but required strict anaerobiosis for growth like their parent strain. The serol. relations between the bacteria and the L type of growth have not yet been studied. The germination of the large bodies could not be studied as well in the other pleomorphic Bacteroides strains as in strain 132. The main reason for this was that the transformation of bacteria into large bodies was not complete in the cultures and the majority of the large bodies were not viable. The large bodies were soon overgrown by bacteria in the transplants. The transformation of the bacteria into large bodies in Str. moniliformis, Escherichia coli and Bacteroides under normal conditions of cultivation is not degenerative but part of a reproductive process.