Phage-like Structures from Lactobacillus acidophilus

Attempts to isolate phages active on strains of Lactobacillus acidophilus from sewage (Coetzee, de Klerk & Sacks, 1960) and by u.v. light-induction of these strains were unsuccessful (Coetzee & de Klerk, 1962). In renewed attempts to derive phages from L. acidophilus, 80 strains were treated with mitomycin C. Early log phase cultures of the L. acidophilus strains in MRS broth (de Man, Rogosa & Sharpe, 1960) were exposed to mitomycin C (1 µg./ml.) for 20 min. at 37°. The cells were harvested and suspended in equal volumes of fresh warm broth and incubated for 6 hr. After centrifugation, culture supernatant fluids were sterilized with chloroform and dilutions spotted on lawns of all the 80 L. acidophilus strains and also 98 Lactobacillus fermenti and 50 Lactobacillus casei strains, as previously described (de Klerk & Coetzee, 1961). No plaques were ever seen, but 16 of the 80 supernatant fluids produced zones of growth inhibition on some of the L. acidophilus indicators.