THE ISOLATION AND CULTIVATION OF LACTOBACILLUS BIFIDUS: A COMPARISON OF BRANCHED AND UNBRANCHED STRAINS

Abstract

The Teply and Elvehjem medium supplemented with folic acid, sorbitan mono-oleate, pancreatin, ascorbic acid, and vitamin B12 is satisfactory for the isolation and propagation of branched L. bifidus from the stools and intestinal content of breast-fed infants. Unbranched strains, probably derived by mutation from branched organisms, occur frequently but can be differentiated readily on agar plates and on stained prepns. of the branched organisms. The bifid organisms growing on a solid medium require small amts. of atm. CO2; they tolerate up to 3% of atm. 02. When grown in broth tubes the organisms tolerate atm. O2 and do not require CO2. The unbranched strains and American Type Culture Collection strains of L. bifidus nos. 4962 and 4963 (now classified as L. acidophilus) and L. acidophilus nos. 4355, 4357, and 9857 growing in either solid or liquid media do not require CO2, will grow aerobically, and are facultative anaerobes. The growth range of bifid organisms at varying temps. is more limited than that of the unbranched strains and ATCC strains of L. bifidus and L. acidophilus no. 4357. Growth of the bifid strains is poor at pH 6 and usually absent at pH 5.6. Maximum growth of unbranched strains and ATCC strains of L. bifidus and L. acidophilus no. 4357 occurs at pH 5.6. None of the bifid strains produce CO2; all but one of the unbranched strains and 3 of 5 ATCC strains produce large amts. of molecular CO2 under the conditions of the expt. Dextro-rotatory lactic acid is formed by the bifid strains and inactive lactic acid by the unbranched strains and ATCC strains. The relative amt. of volatile acid produced by the bifid strains is greatly in excess of that formed by the unbranched and ATCC strains. In both instances, the volatile acid appears to be acetic. None of the organisms listed produces catalase or indole or reduce nitrates to nitrites. Evidence is presented that suggests that unbranched strains may be mutants of branched organisms. It is proposed that the branched organisms the authors have isolated from the stools of breast-fed infants, are the same as those described by Tissier, and that the name L. bifidus should be applied to them rather than the unbranched organisms of Weiss and Rettger; and that the unbranched CO2-producing strains should be called L. parabifidus [n. sp.].