The viable counts of Salmonella typhimurium on nutrient agar (NA) decreased upon the addition of either the essential oil of thyme or its constituent thymol, especially under anaerobic conditions. Antagonistic effects of thymol against Staphylococcus aureus were also greater under anaerobic conditions. In contrast to the phenolic constituents of the oil, thymol and carvacrol, the chemically related terpenes p-cymene and gamma-terpinene had no antagonistic effects against Salm. typhimurium. The addition of Desferal to NA counteracted the antibacterial effects of both thyme oil and thymol. No support was obtained, however, for a possible role of iron in the oxygen-related antibacterial action of the thyme oil and thymol or for the observed effect of Desferal. In the presence of thymol, the viable counts of Salm. typhimurium obtained on a minimal medium (MM) were lower than those obtained on NA. Addition of bovine serum albumin (BSA) neutralized the antibacterial action of thymol. It is suggested that the effects of BSA or Desferal are due to their ability to bind phenolic compounds through their amino and hydroxylamine groups, respectively, thus preventing complexation reactions between the oil phenolic constituents and bacterial membrane proteins. This hypothesis is supported by the marked decrease in the viable counts of Salm. typhimurium caused by either thyme oil or thymol when the pH of the medium was changed from 6.5 to 5.5 or the concentration of Tween 80 in the medium was reduced.

Pediococcus acidilactici SJ-1, isolated from a naturally-fermented meat product, produced an antibacterial agent active against selected strains of Lactobacillus spp., Clostridium perfringens and Listeria monocytogenes. The agent was bactericidal against sensitive indicators, and sensitive to proteolytic enzymes; it was identified as a bacteriocin, and was designated as pediocin SJ-1. It was stable over a wide pH range (3-9), and apparently most stable in the lower part of that range. At pH 3.6, pediocin SJ-1 was stable at heat-processing temperatures within the range 65-121 degrees C; its activity decreased significantly, however, when it was heated at pH 7.0. The activity of pediocin SJ-1 on sensitive indicator cells was lost in the presence of alpha-amylase, suggesting that it contains a glyco moiety, necessary for its antibacterial action. Native pediocin SJ-1 exists in the form of monomers and aggregates (with molecular weights in the range 80-150 kDa). Pediocin SJ-1 was purified 262-fold by direct application of cell-free supernatant fluids to a cation-exchange chromatography column, and was resolved by SDS-PAGE as a single peptide band with a MW of ca 4 kDa. The original pediocin SJ-1-producing strain (bac+) harbours three plasmids of 4.6, 23.5, and 45.7 MDa. Production of pediocin SJ-1, but not immunity to SJ-1, is associated with the 4.6 MDa plasmid.

The production of antagonistic compounds was studied with a strain of Lactobacillus acidophilus isolated from chicken intestinal tract. Accumulation of lactic acid (0.15 mol/l), hydrogen peroxide (280 nmol/h/mg cell dry weight), and a bacteriocin (ca. 10,000 arbitrary activity units per ml) was observed in cultures of this strain. In conditions eliminating the effects of organic acids and hydrogen peroxide, the bacteriocin, designated LA-147, showed inhibitory activity against strains of Lactobacillus leichmannii but not against several other species of Lactobacillus, or other selected gram-positive and gram-negative species. LA-147 (MW ca. 38.5 kDa) was bactericidal against sensitive cells; it was inactivated by heating for 15 min at 100°C, and by the action of protease and alpha-chymotrysin.

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Maltol (3‐hydroxy‐2‐methyl‐4H‐pyran‐4‐one) inhibits the rate of oxidation of different o‐dihydroxyphenols by tyrosinase when assayed spectrophotometrically, but not when assayed polarographically. The spectral changes occurring during the oxidation of different o‐dihydroxyphenols by tyrosinase (or by sodium periodate) in the absence or presence of maltol were different, suggesting that maltol conjugates with the o‐quinones formed. Maltol does not inhibit tyrosinase activity per se but only gives an apparent inhibition probably due to its ability to conjugate with o‐quinones.