MUTATIONS TO ANTIBIOTIC-RESISTANCE OCCUR DURING THE STATIONARY-PHASE IN LACTOBACILLUS-PLANTARUM ATCC-8014

When Lactobacillus plantarum ATCC 8014 was maintained in LCM broth (wh ich consists of buffered tryptone and is sufficient to support the gro wth of some species of Lactobacillus) for long periods (greater than o r equal to 120 d), viable bacteria persisted. Rifampicin-, streptomyci n- and sodium-fusidate-resistant mutants were recovered from parallel LCM broth cultures following a stochastic pattern. Individual cultures appeared to yield mutants intermittently. One culture in particular y ielded rifampicin-resistant colonies at a frequency of 1 in 100 viable bacteria after 20 d incubation and these persisted until the experime nt was terminated at 115 d. In a separate experiment two parallel cult ures yielded mutants resistant to low concentrations of streptomycin a t a similar frequency. Using a chemostat it was shown that in continuo us culture in LCM at slow growth rates the highest frequency of recove ry of antibiotic-resistant mutants was achieved when the bacteria exhi bited doubling times of 90 h or greater. The frequency of recovery of mutants was as high as 1 in 1000 viable bacteria. Thus, mutations to a ntibiotic resistance in L. plantarum ATCC 8014 can take place in the a bsence of measurable cell division. The data are consistent with the n otion that populations of starved bacteria in stationary phase can be genetically dynamic.