Browsing by Subject "heat tolerance"

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  • Pöntinen, Anna; Aalto-Araneda, Mariella; Lindström, Miia; Korkeala, Hannu (2017)
    Listeria monocytogenes is one of the most heat-resistant non-sporeforming food-borne pathogens and poses a notable risk to food safety, particularly when mild heat treatments are used in food processing and preparation. While general heat stress properties and response mechanisms of L. monocytogenes have been described, accessory mechanisms providing particular L. monocytogenes strains with the advantage of enhanced heat resistance are unknown. Here, we report plasmidmediated heat resistance of L. monocytogenes for the first time. This resistance is mediated by the ATP-dependent protease ClpL. We tested the survival of two wildtype L. monocytogenes strains-both of serotype 1/2c, sequence type ST9, and high sequence identity-at high temperatures and compared their genome composition in order to identify genetic mechanisms involved in their heat survival phenotype. L. monocytogenes AT3E was more heat resistant (0.0 CFU/ml log(10) reduction) than strain AL4E (1.4 CFU/ml log(10) reduction) after heating at 55 degrees C for 40 min. A prominent difference in the genome compositions of the two strains was a 58-kb plasmid (pLM58) harbored by the heat-resistant AT3E strain, suggesting plasmid-mediated heat resistance. Indeed, plasmid curing resulted in significantly decreased heat resistance (1.1 CFU/ml log(10) reduction) at 55 degrees C. pLM58 harbored a 2,115-bp open reading frame annotated as an ATP-dependent protease (ClpL)-encoding clpL gene. Introducing the clpL gene into a natively heat-sensitive L. monocytogenes strain (1.2 CFU/ml log(10) reduction) significantly increased the heat resistance of the recipient strain (0.4 CFU/ml log(10) reduction) at 55 degrees C. Plasmid-borne ClpL is thus a potential predictor of elevated heat resistance in L. monocytogenes. IMPORTANCE Listeria monocytogenes is a dangerous food pathogen causing the severe illness listeriosis that has a high mortality rate in immunocompromised individuals. Although destroyed by pasteurization, L. monocytogenes is among the most heat-resistant non-spore-forming bacteria. This poses a risk to food safety, as listeriosis is commonly associated with ready-to-eat foods that are consumed without thorough heating. However, L. monocytogenes strains differ in their ability to survive high temperatures, and comprehensive understanding of the genetic mechanisms underlying these differences is still limited. Whole-genome-sequence analysis and phenotypic characterization allowed us to identify a novel plasmid, designated pLM58, and a plasmid-borne ATP-dependent protease (ClpL), which mediated heat resistance in L. monocytogenes. As the first report on plasmid-mediated heat resistance in L. monocytogenes, our study sheds light on the accessory genetic mechanisms rendering certain L. monocytogenes strains particularly capable of surviving high temperatures-with plasmid-borne ClpL being a potential predictor of elevated heat resistance.
  • Tong, Haibei; Gao, Yan; Li, Jialiang; Li, Jiachen; Huang, Di; Shi, Jisen; Santos, Hélder A.; Xia, Bing (2021)
    Recently, mitochondria‐targeted photothermal nanoagents demonstrated an improved therapeutic efficacy of cancer cells, compared with non‐targeting ones. Herein, copper sulfide (CuS) nanoparticles are in situ synthesized via bovine serum albumin (BSA) templates to prepare photothermal BSA@CuS nanocomposites with high efficiency (42.0%) of photothermal conversion. Subsequently, rhodamine‐110 (R) molecules are covalently conjugated with BSA@CuS nanocomposites to construct mitochondria‐targeted R‐BSA@CuS nanocomposites, which still retained 22.8% of photothermal conversion efficiency. Furthermore, as‐prepared R‐BSA@CuS nanocomposites can be efficiently internalized by human breast cancer (MCF‐7) cells, and then specifically accumulated in their subcellular mitochondria, not lysosomes. Compared with non‐targeting BSA@CuS nanocomposites, these mitochondria‐targeted R‐BSA@CuS nanocomposites show a significant enhancement (***p < 0.001) of their anticancer efficacy under the same near‐infrared irradiation conditions, whose mechanism is further explored in details. Finally, these R‐BSA@CuS nanocomposites can succeed in penetrating in 3D multicellular tumor spheroids composed of MCF‐7 cells. And they also show a significant inhibition effect (**p < 0.01) on the growth of spheroids via photothermal therapy, in contrast to bare BSA@CuS nanocomposites under the same irradiation conditions. Therefore, these mitochondria‐targeted and photothermal R‐BSA@CuS nanocomposites have important potential applications on cancer photothermal therapy with an enhanced efficacy.