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In vitro modeling studies of Lactobacillus acidophilus: Antimicrobial activity and growth
Abstract
Consumption of cultured dairy products results in an increase in the Lactobacillus count and a decrease in coliform count. Hence, model experiments were designed to study the antimicrobial effect of L. acidophilus and the resultant changes in fecal flora. Modeling of in vivo growth and antimicrobial activity of L. acidophilus in vitro requires its growth in the presence physiological concentrations of bile salts. L. acidophilus LA 15 antimicrobial activity was reduced from 20 mm in control to 14.1 mm (12mM of NaTCA or NaGCA) in vitro in the presence of bile salts (0-12 mM) when grown using the conventional technique. The reduction in antimicrobial activity was due to the bacteriocidal effect of accumulating deconjugated bile salts that strongly inhibit the growth of L. acidophilus LA 15 from 8.6 log # cfu/ml (control) to 4.4 log # cfu/ml in the presence of 3 mM NaTCA and 9 mM NaGCA. An "Add-back" in vitro technique has been developed, with the assumption that by periodically centrifuging out the conjugated and deconjugated bile salts, it may be possible to simulate the physiological conditions involving diffusion of conjugated and deconjugated bile salts. With the "Add-back" technique, L. acidophilus LA 15 growth was not inhibited in the presence of 3 mM NaTCA and 9 mM NaGCA concentration, the log # cfu/ml after 24 h were 8.1 and 6.3 in the "Add-back" and conventional techniques, respectively. In the "Add-back" technique the conjugated and deconjugated bile salts are removed periodically enabling the bacteria to grow. The individual and associative growth of E. coli and L. acidophilus was studied by activating the lactoperoxidase (LP) system in vitro. In individual grown cultures, the LP system at 30:30 ppm of hydrogen peroxide:SCN-, was more inhibitory to growth of E. coli (5.5 log # cfu/ml) than L. acidophilus (7.1 log # cfu/ml), as observed in cell counts at the end of 8 h. In associative growth studies at 30:30 ppm of hydrogen peroxide:SCN-, it was observed that the number of viable E. coli (6.0 log # cfu/ml) decreased whereas the number of L. acidophilus (7.0 log # cfu/ml) increased. This suggests that the LP system if activated in vivo may be responsible in part for the alteration in fecal flora.
Subject Area
Food science
Recommended Citation
Fernandes, Custodio F, "In vitro modeling studies of Lactobacillus acidophilus: Antimicrobial activity and growth" (1988). ETD collection for University of Nebraska-Lincoln. AAI8914076.
https://digitalcommons.unl.edu/dissertations/AAI8914076