Protective effect of intranasally inoculated Lactobacillus fermentum against Streptococcus pneumoniae challenge on the mouse respiratory tract

Lactic acid bacteria are increasingly used to restore the ecological equili brium of different mucosal areas in humans and/or animals. Likewise, they c an be used to potentially protect against pathogenic microorganisms. In the present paper, the preventive effect of intranasally inoculated Lactobacil lus fermentum against challenge with Streptococcus pneumoniae was studied, using a mouse experimental model. L. fermentum inoculated four times at a d ose of 10(7) colony forming units per mouse was able to decrease the number of S. pneumoniae throughout the respiratory tract. The L. fermentum treatm ent increased the number of activated macrophages in lung slices, and a hig her lymphocyte population in the tracheal lamina propria. S. pneumoniae cha llenge showed a typical response against pathogen with a higher non-specifi c immune response. Preventive treatment, i.e. L. fermentum administration p rior to S. pneumoniae challenge, showed a response close to that of L. ferm entum. Anti-S. pneumoniae antibodies increased in lactobacilli-treated anim als compared to the non-treated lactobacilli mice. The increase in the anti body levels suggests that the mucosal immune system could be involved in th e protective effect, accomplished with competitive exclusion, nutrient comp etition and production of inhibitory substances. This paper will be the bas is for further studies of the protective effect of lactobacilli against S. pneumoniae in the respiratory tract. (C) 2001 Federation of European Microb iological Societies. Published by Elsevier Science B.V. All rights reserved .