Glutamate Decarboxylase-Mediated Nisin Resistance in Listeria monocytogenes

Abstract

ABSTRACT Analysis of a complete set of glutamate decarboxylase ( gad ) mutants of Listeria monocytogenes strain LO28 (Δ gadD1 , Δ gadDT1 , Δ gadD2 , Δ gadT2 , and Δ gadD3 mutants) revealed that the Δ gadD1 mutant is impaired in its ability to tolerate exposure to both sublethal and lethal levels of the lantibiotic nisin. gadD1 is strain variable and is found only in approximately 50% of L. monocytogenes strains. Growth and survival experiments revealed that possession of gadD1 correlates with a higher degree of tolerance to nisin. Significantly, a similar finding using a gadB mutant of L. lactis IL1403 implies that this may be a general phenomenon in Gram-positive bacteria. Our findings thus suggest that the specific inhibition of GAD activity or a reduction in the levels of free glutamate may prevent the growth of otherwise resistant GAD + bacteria in foods where low pH and/or nisin is used as a preservative.