Additional studies of the pathogenicity of aerobic spore-forming organisms (genus Bacillus) for mice

An investigation of the parenteral pathogenic potential of aerobic spore-forming bacteria (genus Bacillus) in mice revealed that in the case of i.p. inoculation (0.5 ml suspension, 10(6)-10(7) viable cells per ml) only B. cereus was pathogenic, killing appr. one half of the inoculated animals (293 out of 577). Other bacilli (B. subtilis, B. megaterium, B. pumilus etc.) administered intraperitoneally did not produce any lethal effect. If inoculated intracerebrally, B. cereus killed appr. 90% of the mice (138 out of 155), while for other bacilli the rate was appr. 50% only (260 out of 529). It is suggested that most of the aerobic spore-forming organisms cultured from cases of hospital infections are B. cereus which, however, does not completely exclude the presence of other species.