Chloromycetin Resistance in E. coli, a Case of Quantitative Inheritance in Bacteria

DRUG resistance in bacteria has been investigated genetically in several cases, since Demerec began with penicillin resistance in Staphylococcus aureus1. The proposal to distinguish two classes of drug resistance—those in which the top level of resistance can be obtained in a single step, and those in which it can be acquired only gradually—has clearly a practical importance; its theoretical meaning has not been entirely elucidated, since genetical analysis has several limitations in bacteria. In fact, while mutational patterns are open to investigation in most cases, crossings can only be regularly undertaken, as in Lederberg and Tatum's original discovery2, in a few strains of E. coli. In one of these, E. coli K-12, some work on the genetics of drug resistance has been carried out, the most extensive investigation relating to streptomycin. Full resistance in E. coli is developed in a single step3,4.