The adaptation of Bact. lactis aerogenes to growth in the presence of sulphonamides

Abstract

The influence of 2 typical sulfonamides, sulfanilamide and sulfaguanidine, on the growth of Bact. lactis aerogenes (Aerobacter aerogenes) in a synthetic liquid medium has been studied. Increasing cones, of either drug progressively lengthened the lag phase and reduced the growth rate. The latter, however, never reached zero as it does in the presence of other antiseptics. At a certain stage during growth in the presence of the sulfonamide there may be a transition from a slower to a more rapid rate of multiplication. This has been shown to be due to an adaptation of the bacteria. After 30 passages through media containing sulfonamide, the adaptation was almost complete and it was neither specific for a particular sulfonamide'' nor reversible by passage through the normal bouillon medium. The rate of growth may reach that found in sulfonamide-free media. To explain this it was assumed that the cells developed enzymes which produced a sulfonamide antagonist. The establishment of complete adaptation was slow and complex. During the early stages of training the adaptation was specific to one drug, easily lost and only partial. The degree of adaptation attained after 1 or 2 passages through the sulfonamide medium was different from that developed later. This was interpreted as being due to the shortening of the lag of an alternative growth mechanism which was more resistant to sulfonamides than the normal mechanism of growth. The adaptative process is discussed from a physical-chemical basis.