A Comparison of Seven Strains of Lactobacillus casei var. rhamnosus in Relation to their Use in the Microbiological Assay of Serum Folate

Abstract

Summary. A comparison was made of 7 strains of Lactobacillus casei var. rhamnosus in relation to their use in the microbiological assay of serum folate. The problem of clumping by some strains could be overcome by the addition of extra salt, or chloramphenicol, to the medium. The strains showed differences in their tolerance to added salts which was measured as the Mean Inhibitory Salt Concentration. The highest salt concentration which could be used in the assay medium without affecting the serum folate results was about one‐third of the Mean Inhibitory Salt Concentration and this could be less than the optimum concentration for growth. These differences in salt tolerance may provide a partial explanation of the variety of normal values reported from different laboratories.

The Effect of Medium Redox Potential on the Folate-limited Growth of Lactobacillus casei var. rhamnosus

“…The conditions under which cultures were grown were based on the serum folate assay procedure of Tennant & Withey (1972). They were similar to those described previously (Tennant et al 1974) except that the phosphate buffer concentration in the assay medium was decreased to 0.075 M. The pH of the assay medium was 6.35.…”

Effect of Tween 80 on incubation period of Lactobacillus casei assay of serum folate.

“…Others, however, have reported comparable results from 20-and 44-hour assays (Slade et al, 1974;Tennant et al, 1974). Eichner and Dickson (1974) obtained similar results to Streeter and O'Neill (1969) when using BBL folic acid assay PGA broth but not with Difco's Bacto-folic acid casei medium.…”

“…rhamnosus (NCIB 10463) was grown as described previously (Tennant et al, 1974) except that the phosphate buffer concentration was reduced to 0-075 M. BBL folic acid assay PGA broth (Becton Dickinson (UK) Ltd) was used but Tween 80 was not added unless specifically stated.…”