Search

Cronobacter malonaticus is a highly hyperosmotic‐resistant pathogen classified as Class A pathogen by the Food and Agriculture Organization of the United Nations (FAO). This study explored the roles of LuxS as a quorum‐sensing transcription factor in C. malonaticus to tolerate hyperosmotic stress, illustrating that LuxS contributed to survival, biofilm formation and reduced cellular injury when grown with 5.5% NaCl stress. Comparative proteomics between C. malonaticus WT and ΔluxS demonstrated that differentially expressed proteins (DEPs) were abundant in Fe‐S cluster proteins and oxidoreductases, suggesting a potential cross‐tolerance mediated by LuxS could contribute to resisting hyperosmotic stress. Herein, these findings will provide valuable information on LuxS‐mediated osmotic tolerance to controlling C. malonaticus contamination. [ABSTRACT FROM AUTHOR]

Foodborne pathogens detection is important to ensure food safety and human health. In this study, we designed a comet structure to rapidly and sensitively detect foodborne Listeria monocytogenes. This method combined isothermal sequence exchange amplification (SEA) and surface-enhanced Raman spectroscopy. Listeria monocytogenes DNA could be rapidly amplified at a constant temperature via SEA with a pair of modified primers, which rendered the precise thermal control instrumentation unnecessary. Efficient SEA amplification generated a large number of DNA duplexes that could be easily captured by streptavidin-modified magnetic bead and AuMB@Ag-isothiocyanate fluorescein antibody (anti-FITC). AuMB@Ag-anti-FITC was used as a signal probe, which generated a significant excitation signal at 1,616 cm−1 for quantitative detection and analysis. The results displayed sensitive detection of L. monocytogenes in cheese from 2.0 × 101 cfu/mL to 2.0 × 106 cfu/mL within 1.0 h with a detection limit of 7.8 cfu/mL. Furthermore, this comet structure displayed the desirable specificity as its specific primers and amplified DNA ends were attached to streptavidin-modified magnetic beads and AuMB@Ag-anti-FITC, respectively. We expected that the method devised would provide a promising new approach to screening for L. monocytogenes and guarantee the microbiological safety of dairy products. [ABSTRACT FROM AUTHOR]

Cronobacter malonaticus is one of the opportunistic food-borne pathogens in powdered infant formula and has unusual abilities to survive under environmental stresses such as osmotic conditions. However, the genes involved in osmotic stress have received little attention in C. malonaticus. Here, genes involved in osmotic stress were determined in C. malonaticus using a transposon mutagenesis approach. According to the growth of mutants (n = 215) under 5.0% NaCl concentration, the survival of 5 mutants under osmotic stress was significantly decreased compared with that of the wild type strain. Five mutating sites, including potassium efflux protein KefA, inner membrane protein YqjF, peptidylprolyl isomerase, Cys-tRNA(Pro)/CystRNA( Cys) deacylase, and oligogalacturonate lyase were successfully identified. In addition, the biofilm formation of 5 mutants was determined using crystal violet staining, scanning electron microscopy, and confocal laser scanning microscopy, and the biofilms of 5 mutants significantly decreased within 72 h compared with that of wild type strain. This is the first report to determine the genes involved in osmotic tolerance in C. malonaticus. The findings provided valuable information for deep understanding of the mechanism of survival of C. malonaticus under osmotic stress, and a possible relationship between biofilm formation and tolerance to osmotic stress was also demonstrated in C. malonaticus. [ABSTRACT FROM AUTHOR]

Cronobacter malonaticus is one of the important foodborne pathogens causing infections mainly in adults. Biofilm formation, adhesion, and motility in Cronobacter have been documented, but the implying molecular mechanism has received little attention. Here, a comparison in biofilm formation, adhesion ability, and cell motility among wild type (WT), △ luxS , and △ fliC strains were analyzed using scanning electron microscope (SEM) and confocal laser scanning microscopy (CLSM). The thickest biofilm was formed by WT, followed by △ luxS and △ fliC. Furthermore, the deletion of fliC caused the loss of cell motility and the failure to flagella biosynthesis and mature biofilm formation. Besides, the adhesion abilities of △ luxS and △ fliC to biotic cells (LoVo and IEC-6) and abiotic surface (glass) were significantly decreased compared to WT, revealing that fliC might have an important role in the organism's invasion properties. We further demonstrated that the expression of negative regulator (flgM) of flagellin in △ luxS was higher than that in WT, which indicated that luxS indirectly contributed to fliC expression. Our findings provided a novel perspective for precaution and control of C. malonaticus through intercepting fliC -mediated adhesion to biotic cells and abiotic surface. • C. malonaticus △fliC failed to flagella biosynthesis and mature biofilms formation. • Deletion of fliC resulted in the loss of swimming motility and the adhesion to abiotic surfaces and biotic cells;. • C. malonaticus luxS contributed to expression of fliC through negatively regulating flgM. [ABSTRACT FROM AUTHOR]