Acid tolerance in Listeria monocytogenes influences invasiveness of enterocyte-like cells and macrophage-like cells

Clinical and food Listeria monocytogenes isolates, pre-exposed to mild acid ic conditions, were able to readily develop acid tolerance, irrespective of their origin. We attempted to investigate the influence of acid tolerance mechanisms, either constitutive or induced, on the invasive behaviour of th is facultative food-borne pathogen. Entry efficiency and intracellular grow th of acid-tolerant strains were evaluated in in vitro cell models capable to mimic in vivo target cells, such as enterocytes and macrophages. An acid -adapted L. monocytogenes wild-type strain and a constitutively acid-tolera nt mutant were able to enter enterocyte-like (Caco-2) cells as well as to s urvive and proliferate intracellularly in lipopolysaccharide-treated macrop hage-like (J774.A1) cells, at a significant increased extent by respect of the non acid-adapted wild-type strain. These findings add new information a bout the influence of the acid tolerance response on L. monocytogenes virul ence, suggesting that in acid-adapted bacteria the early events of pathogen esis which allow the colonization and the spread of bacteria in the host ma y be highly promoted, (C) 2000 Academic Press.