Journal of food protection最新文献

Although one of the biggest listeriosis outbreaks was reported in South Africa, due to ready-to-eat (RTE) meat product, to date very few data on L. monocytogenes in foods and food environments are available from other African countries. The aims of this study were to: document L. monocytogenes presence in RTE products and food environments from Namibia, Sudan and Zambia, provide isolates genomic characterization, and evaluate genomic similarity using data available at the Italian National Reference Laboratory for L. monocytogenes database. A total of 768 samples, including RTE meat products (n=405), environmental swabs (n=228) and frozen chicken (n=135), were collected and tested for Listeria spp. and L. monocytogenes by African partners. Listeria spp. presence was observed mainly in Zambia (38.7%; n=41/106), followed by Sudan (5.0%; n=24/480) and Namibia (3.3%; n=6/182), mostly related to RTE meat products (10.1%; n=41/405). MALDI-TOF confirmed 14 of 71 strains as L. monocytogenes (n= 12 from meat RTE; n=2 from environments) and MLST identified six CCs: CC9 (n=7), CC1 (n=3), CC3 (n=1), CC37 (n=1), CC121 (n=1) and CC31 (n=1). A complete L. monocytogenes Pathogenicity Island 3 (LIPI-3) was observed in CC1 and CC3 strains, in addition to LIPI-1, which was identified in all 14 strains. Several resistance factors were detected, including stress islands (SSI-1 and SSI-2), Tn6188_qac, cadA and bcr genes. Furthermore, three cgMLST clusters were detected: two for CC9 from Zambia, one for CC1 from Sudan, all related to RTE foods. This study confirmed L. monocytogenes presence in African RTE meat products and food environments, posing a public health concern for consumers, mainly linked to CC1 strain presence, known to be a hyper-virulent clone. Moreover, the presence of L. monocytogenes strains harbouring several resistance factors, such as the CC9 clone, could help these strains to adapt, survive and persist.

The number of farmers' markets (FMs) has steadily increased over the years, creating economic opportunities for farmers. Although fruits and vegetables remain the primary products sold, there is a growing trend of consumers purchasing meat and poultry directly from farmers. As the availability of these products increases, so too does the potential risk of exposure to pathogenic bacteria, underscoring the need for vendor training in microbial safety practices. The objective of this review was to evaluate vendor practices, consumer perceptions, and the microbial safety of meat and poultry sold at FMs. Escherichia coli, Salmonella, and Campylobacter were identified as the most prevalent pathogens associated with these products. Tracking outbreaks linked to FM meat and poultry remains challenging, as the U.S. Centers for Disease Control and Prevention does not specify the source of purchase in outbreak reports. Findings revealed that vendors often lacked adequate handwashing and cross-contamination prevention practices. Many vendors did not perceive the use of additional safety precautions, such as wearing gloves or avoiding direct contact with food, as necessary to prevent microbial contamination during product handling and repackaging. This behavior reflects a broader lack of knowledge and awareness of proper food safety measures. Surveys further indicated that consumers generally perceived meat and poultry sold at FMs as safe, often prioritizing freshness and local sourcing over microbial risk. Overall, this review highlights gaps in vendor behavior and food safety training, emphasizing the need for targeted education and tailored interventions to improve microbial safety in direct-to-consumer meat and poultry sales.

Severe infection caused by Listeria monocytogenes in humans is primarily linked to the pathogen's ability to cross the intestinal barrier and disseminate within the host. Once internalised, L. monocytogenes exhibits intracellular motility that enables colonisation of secondary target organs, including the brain and placenta. This review aims to critically compare the infection pathways of L. monocytogenes in humans and ruminant hosts, highlighting the molecular mechanisms that enable bacterial survival, organ tropism, and adaptation to host-specific stressors. By focusing on these comparative pathways, we aim to clarify how differences in virulence and stress-response factors, influenced by clonal complex, strain type, and lineage, affect host susceptibility and disease outcome. Using a comparative approach, we explore how variation in virulence and stress-response determinants, influenced by lineage, clonal complex, and strain type, may shape host susceptibility and disease outcomes across species. While ruminant listeriosis is well recognized clinically, key aspects of infection dynamics, tissue tropism, and host-pathogen interactions in these hosts remain poorly understood. Addressing these knowledge gaps will strengthen comparative pathogenesis frameworks and enhance the interpretation of strain diversity and host association patterns, contributing to a more integrated understanding of L. monocytogenes biology in human and animal hosts.

Histamine-producing bacteria (HPB) generate histamine in decomposing scombrotoxin-forming fish tissue. Elevated histamine levels (≥200 ppm) can cause scombrotoxin fish poisoning in humans who consume decomposed fish and fishery products. In this study, four psychrotrophic Photobacterium species, P. kishitanii, P. angustum, P. aquimaris, and P. phosphoreum, were evaluated in pure culture for histamine production at 4, 10, and 20°C. P. kishitanii and P. angustum demonstrated the most prolific histamine production in vitro and were inoculated into tuna and mahi-mahi tissue to determine the time at which histamine exceeded FDA guidance levels at 4 and 10°C for P. kishitanii and 10 and 20°C for P. angustum. Current U.S. FDA guidance levels for histamine are ≥200 ppm for human health hazard and ≥35 ppm for evidence of decomposition. Samples were analyzed for histamine with a modified AOAC fluorometric method. Tuna inoculated at 10², 10⁴, and 10⁶ CFU/g P. kishitanii, accumulated histamine levels ≥200 ppm after 7, 5, and 3 days at 4°C and 2, 2, and 1 day(s) at 10°C, respectively. Tuna inoculated at 10², 10⁴, and 10⁶ CFU/g P. angustum, contained histamine levels ≥200 ppm after 6, 4, and 2 days at 10°C and 24, 20, and 12 h at 20°C, respectively. Mahi-mahi inoculated at 10², 10⁴, and 10⁶ CFU/g P. kishitanii, accumulated histamine levels ≥200 ppm after 9, 6, and 4 days at 4°C and 3, 3, and 2 days at 10°C, respectively. Mahi-mahi inoculated at 10², 10⁴, and 10⁶ CFU/g P. angustum, contained histamine levels ≥200 ppm after 10, 9, and 3 days at 10°C and 38, 16, and 12 h at 20°C, respectively. Tissues contained ≥200 ppm histamine after 3-9 days under storage temperature of 4°C but as early as 12 hours when held at elevated temperatures. Understanding how storage conditions affect HPB growth and histamine production in scombrotoxin-forming fish is important to inform guidance for recommended fish storage conditions and to mitigate risks.

This study examined how cellular proximity and inter-strain co-culture influence the time to first division in Listeria monocytogenes C5 (4b serotype) and 6179 (1/2a serotype) strains, previously shown to exhibit strong competitive interactions, using time-lapse microscopy. The strains were inoculated on 4.84 cm² Tryptic Soy Agar with 0.6% Yeast Extract as single or mixed 1:1 co-cultures, under two population densities: dense proximity (DP) and sparse proximity (SP). Phase-contrast images were acquired every 5 min for 2h at 37°C. An in-house-developed program detected and tracked the coordinates of single-cells across the image sequence. A total of 105-143 cells from two independent time-lapse experiments were analyzed to determine the times of the first and second divisions. Across both proximity conditions, singly-cultured 6179 cells showed a higher percentage of first-division events within 2h, along with fewer non-dividing cells and fewer cells reaching a second division. For both strains, the median time to first division was unaffected by cell proximity. In single cultures, 50% of C5 cells completed their first division within 35-40 min, whereas 6179 cells required approximately 60-65 min. In co-culture in SP, 50% of the cells divided for the first time within the first 30 min, almost faster than the singly-cultured strains. In contrast, under DP, the median division time shifted to 50-55 min, indicating that close inter-population proximity can delay first division. These findings indicate that cellular proximity may influence the behavior of the different co-existing strains at a single-cell level.

Biofilms in food processing environments are a major concern for hygiene and food safety as they can harbor spoilage bacteria and pathogens. The aim of this study was to determine the prevalence of biofilms and Listeria (L.) species (spp.) in five Albanian dairies. We analyzed the presence of biofilms on 80 visibly clean sites by enumeration of the bacterial load (>100 bacterial cell equivalents /cm²) and quantification of extracellular DNA, carbohydrates and proteins of the biofilm matrix. We furthermore isolated and characterized Listeria spp. from 200 samples including 80 biofilm and 120 additional samples. The biofilm prevalence (50% of 80 biofilm samples) and Listeria contamination (20% of 200 samples including biofilm and additional samples) was very high, indicating a low hygiene status of the five companies. We detected 40 biofilms in total, including food contact surfaces such as storage tanks. Furthermore, 40 of the 200 sampling sites were positive for Listeria.We isolated 46 strains including 38 L. innocua, 7 L. monocytogenes and 1 L. grayi isolates, resulting in a prevalence of 19% for L. innocua, 3.5% for L. monocytogenes and 0.5% for L. grayi. Listeria were frequently present in biofilms (n=11), 27.5% of 40 biofilms harbored Listeria. The genetic diversity of the L. innocua strains was low, as the isolates mainly belonged to sequence type (ST) 1489 (n=21) and 1085 (n=6). The L. monocytogenes strains, assigned to ST3, ST5 and ST619, harbored the full set of essential virulence genes, indicating a virulent genotype. Gene profiling confirmed the presence of many stress resistance genes in all Listeria spp. strains and the presence of plasmids in 54.3% strains. In conclusion, we successfully identified biofilm and Listeria spp. contamination hotspots in Albanian dairies, which should intensify cleaning and disinfection to improve food safety.

L. monocytogenes is a significant foodborne pathogen associated with serious health risks. The ability to genetically manipulate this bacterium is critical for understanding its pathogenic mechanisms and developing new interventions. However, low transformation efficiency and the absence of natural competence in L. monocytogenes present challenges for genetic studies. We optimized transformation by testing two isolates closely related to widely used laboratory reference strains F2365 and EGD-e (BL87-016 and BL91-025, respectively), and one CC121 isolate (BL87-028-B) that is ecologically relevant to food environments. Increasing the electroporation voltage from 10 to 11 kV/cm resulted in an increase in efficiency. In addition, supplementation with cyclic adenosine monophosphate (cAMP) prior to electroporation increased transformation efficiency in a dose-dependent manner, with an optimal concentration of 32 mM cAMP yielding increases of up to 377-fold. Recognizing the time constraints associated with liquid-based protocols, we developed a rapid agar-lawn method that simplified the workflow and reduced preparation time from approximately 10 h to under 3 h, though efficiencies remained lower than the gold standard method by Monk et al. (2008). The rapid agar-lawn protocol was tested in a panel of 66 L. monocytogenes isolates, with 83% of isolates showing transformability. Transformability showed no statistical correlation between lineage or mobile genetic elements (MGEs). Cooccurrence network analysis of defense and antidefense systems uncovered a higher incidence of interconnected defense repertoires in transformable isolates, suggesting adaptive immune architectures that facilitate DNA uptake. These findings establish optimized protocols and identify potential genomic determinants of transformability under the rapid agar-lawn protocol, broadening genetic accessibility for functional genomics and pathogenesis studies in L. monocytogenes.