Stationary phase cultures of Lactobacillus acidophilus CRL 639 are nat
urally acid resistant to pH 3.0 while exponential phase cells induce a
n acid tolerance response upon exposure to sublethal pH (3.8-6.0). Max
imal response was achieved after adaptation at pH 4.2 and pH 5.0. Prot
ein synthesis was required in the latter case.