Relatedness of Lactobacillus rhamnosus strains isolated from clinical specimens and such from food-stuffs, humans and technology

Abstract

Four hundred and fifty-nine samples of food-stuffs, nonindustrial starter cultures and feces from pigs, cows and healthy humans were screened for the presence of Lactobacillus rhamnosus, and in total 45 strains were isolated. Lactobacillus rhamnosus was frequently found in human feces (39.9%), hard cheese (27.3%) and soft cheese from raw milk (25%) but rarely in raw-milk pools (1.6%) and not at all in feces from cows and pigs. These results suggest that humans are one major reservoir for L. rhamnosus. The isolated strains and five others from infected persons and three used in milk technology were analysed for the presence of macrocapsules, haemolysins, haemagglutination, serum resistance and plasmid DNA. Both macrocapsules and haemagglutination were only demonstrated for one strain each. Antibiogram and plasmid fingerprinting did not discriminate the strains. However, serum resistance testing allowed a certain discrimination. Three strains (5.7%) were partly inactivated, 11 (20.7%) showed a steady state and 39 (73.6%), including all clinical isolates, were able to grow and were therefore clearly serum resistant. The high similarity of the examined strains suggest that a certain potential to cause infection is a characteristic inherent to L. rhamnosus and not limited to a cluster of particular strains. This finding, the fact that infections due to L. rhamnosus are very rare and occur only under certain preconditions and the observation that L. rhamnosus is obviously a part of the normal bacterial flora in the human intestinal tract, should diminish the scepticism in connection with the technological use of this microorganism. However, it must be recommended that L. rhamnosus strains used in fermented or probiotic products are free of macrocapsules, haemagglutination properties, transmissible antibiotic resistances and high level serum resistance. ©1998 Academic Press.