Toxicity of Lactobacillus casei

With the possible exception of Lactobacillus acidophilus, most of the oral lactobacilli are generally considered harmless saprophytes.1 In view of the virulence-enhancing effect of some bacterial capsules, the finding of a heavily encapsulated strain of Lactobacillus casei2 suggested the possibility of another pathogenic lactobacillus. Preliminary serologic studies showed that when whole encapsulated cells of this organism were injected into the marginal ear veins of rabbits, large, indurated, and erythematous lesions developed at the site of injection and became progressively worse. This report describes the toxic property of the organism and its role in the production of both local and systemic lesions using whole cells and several subcellular fractions.