Mechanism of Resistance of Lactic Acid Bacteria to trans-Isohumulone. W. J. Simpson and Jacqueline L. Fernandez, BRF International, Nutfield, Surrey, England RH1 4HY. J. Am. Soc. Brew. Chem. 52:0009, 1994.

Resistance of beer-spoilage lactic acid bacteria to trans-isohumulone is not due to an ability of the organisms to convert the bitter acid to a less inhibitory substance. The bacteria are unable to grow in the absence of a transmembrane pH gradient after it has been dissipated by trans-isohumulone. There are no differences in the amounts of trans-isohumulone that bind to hop-sensitive and hop-resistant organisms. An inability of the antibacterial agent to reach its target is, therefore, unlikely to form the nature of resistance. Unlike sensitive organisms, resistant organisms maintain a transmembrane pH gradient and adenosine 5'-triphosphate pool in the presence of trans-isohumulone. These results suggest that hop resistance has its origins in the cell membranes of bacteria.

Keywords: Hops, Lactobacillus, Pediococcus, Resistance, trans-Isohumulone