Construction of Listeria monocytogenes mutants with in-frame deletions in putative ATP-binding cassette (ABC) transporters and analysis of their growth under stress conditions

Abstract

Listeria monocytogenes is a food-borne pathogen that is difficult to eliminate since it can survive under different stress conditions such as low pH and high salt. Understanding its survival under stress conditions is important in controlling this pathogen in food. ABC transporters have been shown to be induced in L. monocytogenes subjected to high pressure and nisin treatments; therefore, we hypothesized that genes encoding the ABC transporters may be involved in general stress responses. To study the function of these genes, deletion mutants of ABC transporter genes (LMOf2365_1875, LMOf2365_1877) were created in L. monocytogenes F2365, and these deletion mutants were tested under different stress conditions. Compared to the wild type, ΔLMOf2365_1875 and ΔLMOf2365_1877 showed slower growth under nisin (250 μg/ml) and acid (pH 5) treatments. Under salt treatment (5% NaCl in minimal medium), ΔLMOf2365_1877 showed slower growth whereas ΔLMOf2365_1875 had growth similar to the wild type. Moreover, ΔLMOf2365_1875 had an increased capacity to form biofilms compared to the wild type. Our results indicate that these deletion mutants may be more sensitive to multiple stress conditions compared to the wild type, suggesting that LMOf2365_1875 and LMOf2365_1877 may contribute to the general stress response in L. monocytogenes. An understanding of the growth of these mutants under multiple stress conditions and their ability to form biofilms may help in the development of intervention strategies to control L. monocytogenes in food and in the environment. © 2012 Liu Y, et al.