Antibiotic susceptibility of Bacillus species

Organisms of the genus Bacillus are aerobic, spore-forming, usually gram-positive rods which, with the exception of Bacillus anthracis, have been im-plicated infrequently in human disease. These or-ganisms are ubiquitous and commonly occur as contaminants in cultures of clinical material. How-ever, well-documented cases of disseminated in-fection with these organisms in man have been described [1-3]. Recently, we observed a fatal case of pneumonia and bacteremia due to Bacillus cereus in a patient with subacute lymphocytic leu-kemia. Lack of information on the susceptibility of Bacillus species to antimicrobial agents was a handicap in treating this patient. Patients with markedly impaired host resistance are now fre-quently encountered, and information on the anti-microbial susceptibility of "non-pathogenic" bacteria that may infect these patients is desirable. For this reason, the in-vitro susceptibilities to se-lected antibiotics of 49 strains representing six species of Bacillus were studied. Materials and Methods Species of the genus Bacillus were obtained from cultures of sputum, skin, throat, stool, wound, nasopharynx, vaginal discharge, blood, and spinal fluid from the clinical microbiology laboratories of the University of Colorado Medical Center. The organisms were grown on trypticase soy agar con-taining 2.5 % sheep blood; freshly passed cultures Received for publication July 31, 1970, and in revise