ALTERATION IN TRANSFORMABILITY OF DIPLOCOCCUS PNEUMONIAE AFTER THE ACQUISITION OF GENETIC DETERMINANTS INDUCING RESISTANCE TO ERYTHROMYCIN

The Outer Surface Protease, SepM, Is Required for blp Locus Activation in Three of the Four Most Common Pherotypes of Streptococcus pneumoniae

Streptococcus pneumoniae is an important cause of disease in humans that occurs when the bacteria in the nasopharynx bypasses host defenses to invade deeper tissues. Colonization fitness thus represents an important initial step in pathogenesis. S. pneumoniae produces antimicrobial peptides called bacteriocins that provide a competitive advantage over neighboring bacteria in the nasopharynx.

MECHANISM OF RESISTANCE TO ACTINOMYCIN IN BACILLUS SUBTILIS

Polsinelli, M. (University of Pavia, Pavia, Italy), O. Ciferri, G. Cassani, and A. Albertini. Mechanism of resistance to actinomycin in Bacillus subtilis. J. Bacteriol. 88:1567-1572. 1964.-Strains of Bacillus subtilis were rendered resistant to actinomycin D by serial transfer in increasing concentrations of the drug. Resistance to the antibiotic appeared to be due to an altered cell-wall permeability, because the resistant strains did not take up actinomycin. No evidence was found for the presence of an enzyme(s) degrading actinomycin. Deoxyribonucleic acid (DNA) extracted from the actinomycin-resistant strains was found to bind actinomycin to the same extent as the DNA extracted from susceptible strains. The genetic nature of the resistance to actinomycin was demonstrated by means of transformation. Resistant strains appeared to have almost completely lost their transformability, as well as the tendency to autolyze.

Accumulation of 14C-streptomycin by streptomycin-sensitive and streptomycin-resistant group H streptococci

Three streptomycin-resistant mutants of group H streptococcus, strain Challis, were examined for ability to accumulate (14)C-streptomycin. Although the mutants exhibited different levels of transformation, only the streptomycin-sensitive parent Challis strain accumulated significant amounts of (14)C-streptomycin. It appears that impermeability to streptomycin does not necessarily result in reduction or loss of transformability. The amount of label accumulated by strain Challis was correlated with a loss of viability. In addition, accumulation of label was influenced by the concentration of (14)C-streptomycin, the time of exposure, and the type of medium employed.

Transformability of streptomycin-resistant group H streptococci

Several resistant mutants of a transformable group H streptococcus, strain Challis, were isolated from media containing high concentrations of streptomycin. Mutants SR5a and SR5 exhibited high and low transformability, respectively, when exposed to deoxyribonucleic acid (DNA) from a novobiocin-resistant Challis strain. With similar exposure, mutant SR30 exhibited loss of transformability. The mutants further differed from the parent strain in time of appearance of optimal competence, and, in the case of SR5 and SR30, total growth was somewhat less than that of the parent. The rapidity with which transformants appeared upon initial exposure to DNA was approximately the same in the mutants and the parent strain. The decrease or loss of transformability of mutants SR5 and SR30 was found to be due to an alteration in capacity to take up DNA. Mutant SR5a (highly transformable) was further differentiated from mutants SR5 and SR30 in that it was somewhat more sensitive to high concentrations of streptomycin. Transformants obtained by treating strain Challis with the three types of mutant DNA, on the other hand, exhibited similar degrees of resistance to increasing concentrations of streptomycin. The additional decrease in transforming ability of mutant SR5a and the loss of transforming ability of mutant SR5 after a second exposure to streptomycin may indicate a stepwise process in the change from transformability to nontransformability. Although streptomycin resistance may not be directly related to inability to transform, results indicate that streptomycin greatly increases the chances of selecting these mutants and also can be of value in serving as a marker in studies of this nature.