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Infect Immun. 1972 November; 6(5): 785-792
Copyright © 1972 American Society for Microbiology. All Rights Reserved.

Competence of Pneumococcal Isolates and Bacterial Transformations in Man

¹ Department of Microbiology, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21205

ABSTRACT

A survey of pneumococci isolated from 19 healthy carriers and from 23 patients with pneumococcal disease showed that, for both groups, 25 to 30% of the isolates were competent for transformation by soluble deoxyribonucleic acid (DNA) in vitro. Untransformable type 3 and type 8 pneumococci, whose capsules had been hydrolyzed by the Bacillus palustris enzymes prior to exposure to DNA, remained untransformable. Thus, at least for these isolates, it was not the presence of capsule that prevented transformation. Type 9 pneumococci in a healthy human carrier were transformed by DNA released from living unencapsulated pneumococci sprayed onto the pharynx. The donor bacteria were resistant to 1,000 µg of streptomycin/ml. Two types of streptomycin-resistant bacteria were recovered from the carrier's pharynx: a type 9 pneumococcus and an alpha-hemolytic streptococcus. No streptomycin-resistant, gram-positive cocci were isolated from this individual prior to inoculation of the pharynx with the resistant organisms. It seems possible that transformations can occur in the natural environment of some gram-positive cocci.

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