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.
Highlights
Listeria monocytogenes is a food-borne pathogen responsible for human listeriosis, an invasive infection with high mortality rates
L. monocytogenes strain F2365 isolated from Mexican-style soft cheese that was implicated in an outbreak of listeriosis in California in 1985 [33] was used in this study since its genome is fully sequenced and annotated [20]
DNA sequence analysis indicates that the composition of the ATP-Binding Cassette (ABC) transporter operon is comprised of three genes: LMOf2365_1875, LMOf2365_1876 and LMOf2365_1877
Summary
Listeria monocytogenes is a food-borne pathogen responsible for human listeriosis, an invasive infection with high mortality rates. Listeriosis is responsible for an estimated 2500 serious illnesses and 500 deaths each year in the United States, accounting for 28% of annual deaths attributable to known food-borne pathogens, second only to deaths due to Salmonella infections [1]. Transmission of L. monocytogenes is generally through eating contaminated food, in particular, dairy products made from unpasteurized milk and ready-to-eat meat and fish products [3]. L. monocytogenes has been found in a variety of raw foods such as uncooked meats and vegetables, as well as in processed foods that become contaminated after processing, such as soft cheeses and cold cuts at the deli counter [3,4]. Unlike most food-borne pathogens, L. monocytogenes multiplies readily in refrigerated foods [7]
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