Prevalence of Viable Lactobacillus acidophilus in Dried Commercial Products.

Samples of 27 dried acidophilus products used as dietary adjuncts for Lactobacillus acidophilus in humans, were enumerated for viable cells on plate count agar (PCA), MRS broth plus 1.5% agar (MRSA) and MRSA plus 0.15 % oxgall (MRSOA). Colony-forming units did not differ greatly on plating media because most viable cells formed colonies aerobically, anaerobically or in the presence of bile salts. Health food samples had very low numbers of viable cells and counts varied between samples from different lots. Only one of four brands from the health food group had viable L. acidophilus cells. Samples from this group had organisms other than lactobacilli, including coliforms and gram-negative, lactose-negative, motile rods. Most pharmaceutical and milk culture samples had high numbers of viable cells, but only two brands from pharmaceutical samples had viable cells of L. acidophilus . L. acidophilus strains were susceptible to drying, with vacuum drying being more lethal than freeze drying.