METABOLIC AND STRUCTURAL SITES OF DAMAGE IN HEAT-INJURED AND SANITIZER-INJURED POPULATIONS OF LISTERIA-MONOCYTOGENES

Two food isolates of Listeria monocytogenes (strains ATCC 51414 and F5 027) were sublethally injured by exposure to heat (56 degrees C for 20 min) or to a chlorine sanitizer (Antibac, 100 ppm for 2 min). Percent injury following treatment ranged from 84% to 99%. Injured Listeria w ere repaired in Listeria repair broth (LRB) at 37 degrees C. Compariso n of the repair curves generated by each method indicated that the tim e for repair was greater for sanitizer-injured cells (14 h) than for h eat-injured cells (5 h). Sites of injury were determined by repairing heat- and sanitizer-treated Listeria in LRB supplemented with one of t he following inhibitors: rifampicin (10 and 20 mu g/ml), chloramphenic ol (5 mu g/ml), cycloserine D (10 and 20 mu g/ml), and carbonyl cyanid e m-chlorophenyl-hydrazone (CCCP) (2.5 mu g/ml). In both heat- and san itizer-injured populations, a total inhibition of repair was seen foll owing incubation with rifampicin, chloramphenicol and CCCP. These resu lts clearly indicate a requirement for mRNA, protein synthesis, and ox idative phosphorylation for repair to occur. The cell wall is not a si te of damage since cycloserine D had no effect on repair of heat- or s anitizer-injured Listeria. Investigation of damage to the cell membran e showed that stress caused by sublethal heat or sanitizer did not all ow proteins or nucleotides to leak into the medium. The recognition of injury and repair in Listeria will lead to improved methods of detect ion and ultimately to control strategies which prevent outgrowth of th is organism in foods.