MECHANISM OF RESISTANCE OF LACTIC-ACID BACTERIA TO TRANS-ISOHUMULONE

Resistance of beer-spoilage lactic acid bacteria to trans-isohumulone is not due to an ability of the organisms to convert the bitter acid t o 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-i sohumulone 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 organism s, resistant organisms maintain a transmembrane pH gradient and adenos ine 5'-triphosphate pool in the presence of trans-isohumulone. These r esults suggest that hop resistance has its origins in the cell membran es of bacteria.