STUDIES ON ANTIBIOTIC RESISTANCE AND THE NUCLEIC ACID CONTENT OF BACTERIA

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Abstract
Progeny of the same suspension of Hemophilus pertussis show differences in resistance to streptomycin, depending on the culture medium used. On Bordet-Gengou medium a minute proportion of the total population is resistant to streptomycin. This is a typical example of selection. On Cohen-Wheeler medium a very large proportion of the total population (about 40%) is resistant to streptomycin. This cannot be explained on a basis of selection and must occur as a result of environment. Similar activity is exhibited by Micrococcus pyogenes var. aureus except that all of the colonies in this population are resistant on Cohen-Wheeler medium. Expts. demonstrate that the resistance of bacterial spp. grown on Cohen-Wheeler medium is due not to neutralization of the antibiotic by the medium, but to changes in the bacteria which produce resistance to antibiotic. A marked rise in ribonucleic acid content occurs with increase in resistance, whether this resistance is a result of selection or environment. If the population is transferred from Cohen-Wheeler medium to Bordet-Gengou medium it becomes susceptible to antibiotic and the ribonucleic acid content of the bacteria decreases. Bordet-Gongou medium may be substituted for streptomycin as a nutritional source for a streptomycin dependent strain of H. pertussis. When H. pertussis is made resistant to terramycin by the usual method of subculturing in increasing concns. of the antibiotic, a sharp rise in ribonucleic acid content is observed.