Food microbiology最新文献

Histamine is predominantly produced in sausages via the decarboxylation of histidine by bacteria. Furthermore, histamine-producing bacteria usually possess the enzyme histidine decarboxylase (hdc). Enterobacter hormaechei RH3 isolated from sausages exhibited significant levels of histamine production despite the absence of hdc. In this study, we elucidated the previously unidentified mechanism underlying histamine production by RH3. We identified an enzyme, NehdX-772, exhibiting the hdc activity from the cell lysate supernatant of RH3, which was annotated as ornithine decarboxylase. The optimal activity of NehdX-772 was recorded at 35 °C and pH 6.0, and it could tolerate a salt concentration of 2.5% (w/v) NaCl. Moreover, artificial inoculation revealed that NehdX-772 was synthesized at significant levels in sausages, leading to an increase in histamine levels. The discovery of NehdX-772 explains the underlying mechanism of histamine production by RH3 and can be applied to decrease histamine production in sausages.

Saccharomyces cerevisiae SPC-SNU 70-1 is a commercial diploid baking yeast strain valued for its excellent bread-making qualities, including superior leavening capabilities and the production of flavor-enhancing volatile organic acids. Despite its benefits, this strain faces challenges in fermenting both lean (low-sugar) and sweet (high-sugar) doughs. To address these issues, we employed the CRISPR/Cas9 genome editing system to modify genes without leaving any genetic scars. For lean doughs, we enhanced the yeast's ability to utilize maltose over glucose by deleting a gene involved in glucose repression. For sweet doughs, we increased glycerol production by overexpressing glycerol biosynthetic genes and optimizing redox balance, thereby improving the tolerence to osmotic stress during fermentation. Additionally, the glycerol-overproducing strain demonstrated enhanced freeze tolerance, and bread made from this strain exhibited improved storage properties. This study demonstrates the feasibility and benefits of using engineered yeast strains, created solely by editing their own genes without introducing foreign genes, to enhance bread making.

To prevent foodborne illness, adequate cleaning and disinfection (C&D) is essential to remove pathogenic bacteria from the slaughter environment. The aim of this study was to determine the presence of Campylobacter spp., Listeria monocytogenes, and extended-spectrum beta-lactamase-producing Escherichia coli (ESBL E. coli) before and after C&D in slaughterhouses.

Samples from food- and non-food contact surfaces taken before and after C&D in one red meat and one poultry slaughterhouse were analyzed for the target bacteria. Whole-genome sequencing and antimicrobial susceptibility testing were performed.

In total, 484 samples were analyzed. Campylobacter spp. were isolated from 13.0% to 15.5% of samples before C&D in the red meat and poultry slaughterhouse, respectively. Listeria monocytogenes was isolated before C&D in 12.5% and 5.2% of samples in the red meat and poultry slaughterhouse, respectively. It was noted that C. jejuni was detected on multiple surfaces and that L. monocytogenes showed potential persistence in one slaughterhouse. After C&D, L. monocytogenes was found in one sample. ESBL E. coli was not detected either before or after C&D.

These findings show the possibility to remove pathogenic bacteria from slaughter and meat processing facilities, but also indicate that deficiencies in slaughter hygiene pose a risk of cross-contamination of meat.

Food contamination and biofilm formation by Shigella in food processing facilities are major causes of acute gastrointestinal infection and mortality in humans. Bacteriophages (phages) are promising alternatives to antibiotics in controlling plankton and biofilms in food matrices. This study isolated two novel phages, S2_01 and S2_02, with lytic activity against various Shigella spp. From sewage samples. Transmission electron microscopy revealed that phages S2_01 and S2_02 belonged to the Caudovirales order. On characterizing their lytic ability, phage S2_01 initially exhibited relatively weak antibacterial activity, while phage S2_02 initially displayed rapid antibacterial activity after phage application. A combination of these phages in a 1:9 ratio was selected, as it has been suggested to elicit the most rapid and sustained lysis ability for up to 24 h. It demonstrated lytic activity against various foodborne pathogens, including six Shigella spp. The phage cocktail exhibited biofilm inhibition and disruption abilities of approximately 79.29% and 42.55%, respectively, after 24 h in a 96-well microplate. In addition, inhibition (up to 23.42%) and disruption (up to 19.89%) abilities were also observed on stainless steel surfaces, and plankton growth was also significantly suppressed. Therefore, the phage cocktail formulated in this study displays great potential as a biological control agent in improving food safety against biofilms and plankton.

Botrytis cinerea, which causes postharvest gray mold, is a primary pathogen that limits grape shelf-life and consumption and causes substantial yield loss worldwide. The combined use of biocontrol agents and food additives has attracted increasing interest. The effects of combined treatment with the endophyte Bacillus subtilis K1 and sodium dehydroacetate (SD) on the occurrence of gray mold and maintenance of grape fruit quality were studied. Treatment with a K1 suspension (1 × 10⁸ CFU/ml) combined with 0.32 g/L SD resulted in markedly improved control of B. cinerea on grapes. The disease incidence and severity in the groups treated with K1 alone or in combination with SD were significantly lower than those in the control groups (P < 0.05) when the mixtures were applied 2 h after pathogen inoculation. Moreover, application of the mixture could maintain the appearance, firmness, total soluble solid (TSS) content and titratable acidity (TA) of grape fruit. Furthermore, the combination triggered increases in the activities of defense-related enzymes such as peroxidase (POD), phenylalanine ammonia lyase (PAL), catalase (CAT), superoxide dismutase (SOD) and polyphenol oxidase (PPO). Additionally, it could increase the vitamin C content. Thus, appropriate combinations of biocontrol agents and chemical reagents can provide effective protection against postharvest decay.

This study was designed to evaluate the combination effects of antimicrobial peptides (FK13 and FK16) and phage-encoded endolysin (LysPB32) on the inhibition of growth of polymyxin B-resistant Salmonella Typhimurium ATCC 19585 (ST^PMB). The inhibitory effects of FK13, FK16, and LysPB32 against ST^PMB were evaluated by using antimicrobial susceptibility, membrane permeability, biofilm reduction, cross-resistance, and mutant frequency assay. The minimum inhibitory concentrations (MICs) of FK13 and FK16 treated with LysPB32 (FK13+LysPB32 and FK16+LysPB32) against ST^PMB were decreased from more than 512 to 128 μg/ml and from 64 to 32 μg/ml, respectively. Compared to the control, the number of ST^PMB in the growing culture was reduced by 4.2 and 5.2 log CFU/ml, respectively, for FK13+LysPB32 and FK16+LysPB32 after 12-h incubation at 37 °C. All treatments (FK13, FK16, FK13+LysPB32, FK16+LysPB32) significantly increased the permeability of the outer membrane of ST^PMB. Biofilms were significantly decreased from OD₆₀₀ of 0.6 to 0.16 for FK13+LysPB32 and from 0.6 to 0.13 for FK16+LysPB32. The ratios of MICs of erythromycin, ceftriaxone, polymyxin B, and ciprofloxacin to MIC of the control against ST^PMB were decreased to 0.50 for FK13+LysPB32 and FK16+LysPB32. The bactericidal activities of amikacin and gentamicin were enhanced for FK13+LysPB32 and FK16+LysPB32 (2-fold < MBC/MIC ratio). The mutant frequencies of ST^PMB to antibiotics were decreased when treated with FK13+LysPB32 and FK16+LysPB32. The results suggest that the combination of antimicrobial peptides and endolysins can be a promising strategy to control polymyxin B-resistant S. Typhimurium.

Clostridium perfringens, as a foodborne pathogen, can cause various intestinal diseases in both humans and animals according to its repertoire of toxins. In recent years, a multitude of studies have highlighted its threat to infants and young children. C. perfringens carries numerous toxins, with the newly identified BEC toxin confirmed as the second toxin to cause diarrheal illness, after CPE. However, the global dissemination of C. perfringens strains carrying becAB genes, which encode BEC toxins, has not been extensively studied. Following epidemiological surveillance of the prevalence of C. perfringens from different sources in various provinces of China, we identified two becAB-carrying strains and one strain carrying a sequence similar to becAB from distinct provinces and sources. When combined with genomic analysis of other becAB-carrying C. perfringens strains from public databases, we found that becAB was present in strains from different lineages. Our analysis of the plasmid and genetic environment corroborates previous findings on becAB-carrying strains, confirming that it currently achieves horizontal transmission through one type of evolutionarily conserved Pcp plasmid. This study provides a comprehensive analysis of the prevalence and transmission patterns of the newly emerged toxin gene locus, becAB, in C. perfringens. Despite the relatively low identification rate of becAB-carrying strains, their potential impact requires ongoing surveillance and investigation of their features, particularly their antimicrobial resistance.

Despite numerous studies evaluating the antimicrobial activity of essential oil components (EOCs) against different microorganisms, the effect of the composition of the matrix in which they are applied remains unexplored. Hence, the effect of different food components (i.e., proteins, lipids, carbohydrates, acids, ethanol) on vanillin antimicrobial activity was carried out by assessing the growth of E. coli at different incubation times (0, 1, 4, 8 and 24 h). Based on these outcomes, the food components that most adversely affected vanillin antimicrobial activity were subsequently tested with four other EOCs (i.e., carvacrol, eugenol, geraniol, thymol). The effective concentration of antimicrobials after coming into contact with food components was quantified. The results indicated that bovine serum albumin (BSA), sunflower oil and carbohydrates partially or completely inhibited the antimicrobial efficacy of the tested EOCs, and the inhibition rate depended on the specific EOC-food component combination. Geraniol was notably the most efficient with BSA present. Eugenol performed best with sunflower oil. Carvacrol, eugenol, geraniol and thymol were more effective than vanillin with D-lactose present. This study confirmed that loss of EOCs’ effective concentration due to an interaction with food constituents is a significant cause of antimicrobial activity inhibition. These findings underscore the importance of considering matrix composition when selecting antimicrobials to combat a particular strain in real food applications.