THE presence of unusual forms in bacterial cultures has been recognized for many years. Such organisms, which were called pleuropneumonia-like (PPL), were the center of considerable controversy and were thought at one time to be causal agents in various diseases. Morphologically, these organisms differed so strikingly from bacteria that they were classified as an independent order or even in an independent class.1 In 1935 Klieneberger2 isolated from cultures of Streptobacillus moniliformis organisms which resembled bovine pleuropneumoniae and designated them as L 1. Originally it was thought that such organisms were distinct from S. moniliformis and lived in symbiosis with this organism.
In recent years the error of this view has been recognized, since similar forms of many micro-organisms have been identified. It is now known that culture of many micro-organisms under various conditions, such as in the presence of antibiotics, other bacteriostatic chemicals, phage, and antibodies, results in
NEWER CONCEPTS IN BACTERIOLOGY. JAMA. 1960;173(5):544–545. doi:10.1001/jama.1960.03020230070010
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