Aims: To evaluate the effects of different physico-chemical factors on the growth and auto-aggregating ability of vaginal Lactobacillus johnsonii CRL 1294. Methods and Results: L. johnsonii CRL 1294 was cultivated in different culture media, initial pH and temperature of incubation. The growth parameters were estimated by the Gompertz model, being optimal ( higher final biomass and growth rate, and shorter lag phase) at an initial pH of 6 5 and at a temperature of 37 degrees C, both in LAPTg and MRS. The auto-aggregation ability, which was assessed by a model of exponential association, was evidenced in all the growth phases, being higher at pH 5 or 6(.)5. Conclusions: The growth of L. johnsonii CRL 1294 was affected in different way by all the physico-chemical factors tested. However, the auto-aggregation ability increased mainly at low initial pH of growth media. Significance and Impact of the Study: The auto-aggregation ability under different culture conditions of a vaginal Lactobacillus strain was systematically and statistically evaluated for the first time. The higher cellular aggregation evidenced at low pH could be a fundamental characteristic in the acidic vaginal environment to promote the protective role of lactobacilli.