Prevalence of multidrug resistant Salmonella spp. in dairy products with the evaluation of the inhibitory effects of ascorbic acid, pomegranate peel extract, and D-tryptophan against Salmonella growth in cheese

Food Pathways of Salmonella and Its Ability to Cause Gastroenteritis in North Africa

Infections caused by human pathogenic bacteria in food sources pose significant and widespread concerns, leading to substantial economic losses and adverse impacts on public health. This review seeks to shed light on the recent literature addressing the prevalence of Salmonella in the food supply chains of North African countries. Additionally, it aims to provide an overview of the available information regarding health-related concerns, such as virulence genes, and the presence of antibiotic resistance in Salmonella. This review highlights a gap in our comprehensive understanding of Salmonella prevalence in the food supply chains of North African nations, with limited molecular characterization efforts to identify its sources. Studies at the molecular level across the region have shown the diversity of Salmonella strains and their virulence profiles, thus, these results show the difficulty of controlling Salmonella infections in the region. In addition, the discussion of antibiotic resistance makes it clear that there is a need for the development of comprehensive strategies to fight the potential threat of antimicrobial resistance in Salmonella strains. Despite common reports on animal-derived foods in this region, this review underscores the persistent challenges that Salmonella may pose to food safety and public health in North African countries.

Biological function of d-tryptophan: a bibliometric analysis and review

Background

d-Tryptophan is recognised for its unique physiological properties. In this study, we aimed to explore the dynamic trends and emerging topics in d-tryptophan research to offer fresh perspectives for future studies.

Methods

Employing bibliometric analysis, we examined the literature on d-tryptophan indexed in the Web of Science Core Collection from January 1987 to December 2023. The "Bibliometrix" R package and CiteSpace were utilised for data processing.

Results

Analyses of 865 publications revealed 2209 keywords, 4068 authors, 2094 institutions, and contributors from 302 regions. The USA was at the forefront of publications concerning d-tryptophan, but the European Journal of Pharmacology, Journal of Biological Chemistry, and Journal of Medicinal Chemistry were notable for their contributions, co-citations, and impact, respectively. This literature review reveals that since 1987, studies have developed from a focus on d-tryptophan metabolism to the exploration of its functions in organic and medicinal chemistry and food science. Recent findings highlight the potential of d-tryptophan as a non-nutritional sweetener and food preservative as well as its role in inhibiting the growth of bacterial biofilms. Additionally, its immunomodulatory properties are being investigated in relation to allergic diseases. Furthermore, d-tryptophan plays a role in the therapy of atherosclerosis, osteoporosis, tuberculosis, and cancer.

Conclusion

The results of bibliometric analysis highlight that future research should focus on the biological functions of d-tryptophan as a food preservative and its use in immunomodulation and drug development, providing strong guidance for future research.

Biofilm formation in food industries: Challenges and control strategies for food safety

Various pathogens have the ability to grow on food matrices and instruments. This grow may reach to form biofilms. Bacterial biofilms are community of microorganisms embedded in extracellular polymeric substances (EPSs) containing lipids, DNA, proteins, and polysaccharides. These EPSs provide a tolerance and favorable living condition for microorganisms. Biofilm formations could not only contribute a risk for food safety but also have negative impacts on healthcare sector. Once biofilms form, they reveal resistances to traditional detergents and disinfectants, leading to cross-contamination. Inhibition of biofilms formation and abolition of mature biofilms is the main target for controlling of biofilm hazards in the food industry. Some novel eco-friendly technologies such as ultrasound, ultraviolet, cold plasma, magnetic nanoparticles, different chemicals additives as vitamins, D-amino acids, enzymes, antimicrobial peptides, and many other inhibitors provide a significant value on biofilm inhibition. These anti-biofilm agents represent promising tools for food industries and researchers to interfere with different phases of biofilms including adherence, quorum sensing molecules, and cell-to-cell communication. This perspective review highlights the biofilm formation mechanisms, issues associated with biofilms, environmental factors influencing bacterial biofilm development, and recent strategies employed to control biofilm-forming bacteria in the food industry. Further studies are still needed to explore the effects of biofilm regulation in food industries and exploit more regulation strategies for improving the quality and decreasing economic losses.

Combined Ascorbic Acid and Mild Heat Treatment to Improve the Quality of Fresh-Cut Carrots

Mild heat (MH) treatment and ascorbic acid (AsA) addition can improve the quality of fresh-cut produce when used individually; however, their combined effect remains unclear. Herein, fresh-cut carrots were used as models to explore the effects of MH (50 °C)-AsA (0.5%) on quality properties including reactive oxygen species (ROS) metabolism, antioxidants, lignin metabolism, naturally present microbes, and inoculated pathogens (Escherichia coli O157: H7 and Salmonella Typhimurium) during storage (0-5 d, 4 °C). The results indicate that the antioxidant properties in the MH-AsA group were consistent with those of single treatments, resulting in a consistent ROS-scavenging effect. From day 3-5, lignin synthesis was significantly inhibited by MH-AsA as compared with single treatments, probably because the two enzymes (phenylalanine ammonia-lyase and peroxidase) responsible for lignin synthesis exhibited lower expressions. Microbial analysis revealed that MH-AsA treatment led to the lowest counts of both pathogens and aerobic mesophilic bacteria at 0-5 d. Conversely, the inhibitory effect of MH-AsA treatment on mold and yeast was consistent with the single treatments. These results suggest that MH-AsA is a low-cost and safe approach to improve the physiological characteristics of fresh-cut produce while reducing microbial risk.

Rumi and Pasteurized Kareish Cheeses Are a Source of β-Lactam-Resistant Salmonella in the Nile Delta Region of Egypt: Insights into Their Incidence, AMR Pattern, Genotypic Determinants of Virulence and β-Lactam Resistance

The spread of superbugs in dairy products can jeopardize global public health. To date, information on the incidence rates of virulent and β-lactams-resistant (BLR) Salmonella in cheeses from rural areas of Egypt has been lacking. Biochemical, serological, antibiotic susceptibility, and multiplex PCR (M-PCR) tests were performed to identify and characterize Salmonella isolates. In this study, 44 (15.71%) Salmonella isolates of eight different serotypes were recovered from 280 samples of Rumi and pasteurized Kariesh cheeses across the Nile Delta region of Egypt. The most predominant serotypes were S. Typhimurium, S. Enteritidis, and S. Infantis. The virulence genes (invA, stn, and hilA) were identified in all isolates. However, spvC was only detected in S. Typhimurium. The highest resistance was developed against Erythromycin and Clindamycin (90.91%), followed by Ceftazidime and Cephalothin (84.09%). Meropenem and colistin were the most effective antibiotics. A high proportion (79.55%) of multi-drug resistance (MDR) isolates carried narrow spectrum (NS), extended-spectrum (ES), and AmpC-BLR genes. The blaOXA-1, blaOXA-2, blaTEM-1, blaCTX-M, blaCMY-1, and blaCMY-2 BLR genes were positive in 37.04%, 29.63%, 25.93%, 14.81%, 37.04%, and 3.70% of isolates, respectively. In conclusion, a high prevalence of virulence and BLR genes harboring Salmonella strains in Egyptian cheeses is considered a great threat to public health.

D-tryptophan, an eco-friendly natural, safe, and healthy compound with antimicrobial activity against food-borne pathogens: A systematic review

Recently, the use of D-amino acids as food preservatives has attracted considerable attention because these natural compounds do not have adverse effects on human health. In addition, D-amino acids such as D-tryptophan can reduce the harmful effects of other treatments. For instance, the use of D-tryptophan in food reduces the requirement for high temperatures and their damaging effects on nutrients such as proteins and vitamins. The purpose of this systematic review was to investigate the antimicrobial effect of D-tryptophan on food-borne pathogens in vitro and in food models. To identify related studies, scientific digital databases such as PubMed, Science Direct, and Google Scholar were searched from January 2000 to February 2023. The results of the studies showed that when D-tryptophan was used with other stresses such as using different salt concentrations, refrigeration, or high temperatures, it showed significant antimicrobial effects on Gram-positive and Gram-negative food-borne pathogens, and antibiofilm impacts were also observed with D-tryptophan. Since studies have shown that the antimicrobial activity of D-tryptophan depends on several factors, including the pathogen strain, the type of stress, and the concentration of D-tryptophan, and every article has focused on one of these factors, there is a need for a systematic review that summarizes and concludes the effect of all these factors on the antimicrobial activity of D-tryptophan against food-borne pathogens.

Utilization of Whey for Eco-Friendly Bio-Preservation of Mexican-Style Fresh Cheeses: Antimicrobial Activity of Lactobacillus casei 21/1 Cell-Free Supernatants (CFS)

Using whey, a by-product of the cheese-making process, is important for maximizing resource efficiency and promoting sustainable practices in the food industry. Reusing whey can help minimize environmental impact and produce bio-preservatives for foods with high bacterial loads, such as Mexican-style fresh cheeses. This research aims to evaluate the antimicrobial and physicochemical effect of CFS from Lactobacillus casei 21/1 produced in a conventional culture medium (MRS broth) and another medium using whey (WB medium) when applied in Mexican-style fresh cheese inoculated with several indicator bacteria (Escherichia coli, Salmonella enterica serovar Typhimurium, Staphylococcus aureus, and Listeria monocytogenes). The CFSs (MRS or WB) were characterized for organic acids concentration, pH, and titratable acidity. By surface spreading, CFSs were tested on indicator bacteria inoculated in fresh cheese. Microbial counts were performed on inoculated cheeses during and after seven days of storage at 4 ± 1.0 °C. Moreover, pH and color were determined in cheeses with CFS treatment. Lactic and acetic acid were identified as the primary antimicrobial metabolites produced by the Lb. casei 21/1 fermentation in the food application. A longer storage time (7 days) led to significant reductions (p < 0.05) in the microbial population of the indicator bacteria inoculated in the cheese when it was treated with the CFSs (MRS or WB). S. enterica serovar Typhimurium was the most sensitive bacteria, decreasing 1.60 ± 0.04 log10 CFU/g with MRS-CFS, whereas WB-CFS reduced the microbial population of L. monocytogenes to 1.67 log10 CFU/g. E. coli and S. aureus were the most resistant at the end of storage. The cheese's pH with CFSs (MRS or WB) showed a significant reduction (p < 0.05) after CFS treatment, while the application of WB-CFS did not show greater differences in color (ΔE) compared with MRS-CFS. This study highlights the potential of CFS from Lb. casei 21/1 in the WB medium as an ecological bio-preservative for Mexican-style fresh cheese, aligning with the objectives of sustainable food production and guaranteeing food safety.

Punicalagin, a pomegranate polyphenol sensitizes the activity of antibiotics against three MDR pathogens of the Enterobacteriaceae

BACKGROUND

Multidrug resistance (MDR) in the family Enterobacteriaceae is a perniciously increasing threat to global health security. The discovery of new antimicrobials having the reversing drug resistance potential may contribute to augment and revive the antibiotic arsenal in hand. This study aimed to explore the anti-Enterobacteriaceae capability of bioactive polyphenols from Punica granatum (P. granatum) and their co-action with antibiotics against clinical isolates of Enterobacteriaceae predominantly prevalent in South Asian countries.

METHODS

The Kandhari P. granatum (Pakistani origin) extracts were tested for anti-Enterobacteriaceae activity by agar well diffusion assay against MDR Salmonella enterica serovar Typhi, serovar Typhimurium and Escherichia coli. Predominant compounds of active extract were determined by mass spectrometry and screened for bioactivity by agar well diffusion and minimum inhibitory concentration (MIC) assay. The active punicalagin was further evaluated at sub-inhibitory concentrations (SICs) for coactivity with nine conventional antimicrobials using a disc diffusion assay followed by time-kill experiments that proceeded with SICs of punicalagin and antimicrobials.

RESULTS

Among all P. granatum crude extracts, pomegranate peel methanol extract showed the largest inhibition zones of 25, 22 and 19 mm, and the MICs as 3.9, 7.8 and 7.8 mg/mL for S. typhi, S. typhimurium and E. coli, respectively. Punicalagin and ellagic acid were determined as predominant compounds by mass spectrometry. In plate assay, punicalagin (10 mg/mL) was active with hazy inhibition zones of 17, 14, and 13 mm against S. typhi, S. typhimurium and E. coli, respectively. However, in broth dilution assay punicalagin showed no MIC up to 10 mg/mL. The SICs 30 μg, 100 μg, and 500 μg of punicalagin combined with antimicrobials i.e., aminoglycoside, β-lactam, and fluoroquinolone act in synergy against MDR strains with % increase in inhibition zone values varying from 3.4 ± 2.7% to 73.8 ± 8.4%. In time-kill curves, a significant decrease in cell density was observed with the SICs of antimicrobials/punicalagin (0.03-60 μg/mL/30, 100, 500 μg/mL of punicalagin) combinations.

CONCLUSIONS

The P. granatum peel methanol extract exhibited antimicrobial activity against MDR Enterobacteriaceae pathogens. Punicalagin, the bacteriostatic flavonoid act as a concentration-dependent sensitizing agent for antimicrobials against Enterobacteriaceae. Our findings for the therapeutic punicalagin-antimicrobial combination prompt further evaluation of punicalagin as a potent activator for drugs, which otherwise remain less or inactive against MDR strains.

Assessment of the Microbiological Safety and Hygiene of Raw and Thermally Treated Milk Cheeses Marketed in Central Italy between 2013 and 2020

A profile of the microbial safety and hygiene of cheese in central Italy was defined based on an analysis of 1373 cheeses sampled under the Italian National Control Plan for Food Safety spanning the years 2013 to 2020 and tested according to Commission Regulation (EC) No. 2073/2005 (as amended). A total of 97.4% of cheese samples were assessed as being satisfactory for food safety criteria and 80.5% for process hygiene criteria. Staphylococcal enterotoxin was found in 2/414 samples, while Salmonella spp. and Listeria monocytogenes were detected in 15 samples out of 373 and 437, respectively. Escherichia coli and coagulase-positive staphylococci counts were found unsatisfactory in 12/61 and 17/88 cheese samples, respectively. The impact of milking species, milk thermal treatment, and cheese hardness category was considered. A statistically significant association (p < 0.05) was found between milk thermal treatment and the prevalence of coagulase-positive staphylococci and Listeria monocytogenes and between hardness and unsatisfactory levels of Escherichia coli. The data depict a contained public health risk associated with these products and confirm, at the same time, the importance of strict compliance with good hygiene practices during milk and cheese production. These results can assist in bolstering risk analysis and providing insights for food safety decision making.

Multiplex polymerase spiral reaction for simultaneous detection of Salmonella typhimurium and Staphylococcus aureus

Salmonella typhimurium (S. typhimurium) and Staphylococcus aureus (S. aureus) are common food-borne pahogens that cause food poisoning in humans. In this study, we developed a method for the simultaneous determination of S. typhimurium and S. aureus based on multiplex polymerase spiral reaction (m-PSR) and melting curve analysis. Two pairs of primers were designed specifically to target the conserved invA gene of S. typhimurium and nuc gene of S. aureus, and the nucleic acid amplification reaction was achieved under isothermal conditions in the same reaction tube for 40 min at 61 °C, melting curve analysis of the amplification product was carried out. The distinct mean melting temperature allowed simultaneous differentiation of the two target bacteria in the m-PSR assay. The limit of detection of S. typhimurium and S. aureus that could be detected simultaneously was 4.1 × 10^-4 ng genomic DNA and 2 × 10¹ CFU/mL pure bacterial culture. Based on this method, analysis of artificially contaminated samples showed excellent sensitivity and specificity consistent with those of pure bacterial cultures. This method is rapid, simultaneous and promises to be a useful tool for the detection of food-borne pathogens in the food industry.

Combination of ultrasound-peracetic acid washing and ultrasound-assisted aerosolized ascorbic acid: A novel rinsing-free disinfection method that improves the antibacterial and antioxidant activities in cherry tomato

Traditional ultrasound (US)-assisted disinfection is only effective during washing. Coating is an effective method to control microbial growth after washing; however, cross-contamination can occur during immersion in the coating aqueous solution. Tap water (TW) rinsing is generally used to remove sanitizer residues after US-assisted washing; however, the Food and Drug Administration stated that rinsing is unnecessary when the peracetic acid (PAA) concentration does not exceed 80 ppm. In this study, we proposed a novel US-assisted hurdle technology of 80 ppm PAA combined with low-frequency US (25 kHz) during washing, followed by US-assisted aerosolization processing (nonimmersion coating). Ascorbic acid (AA), a safe and low-cost agent, was selected as the aerosolization solution. Cherry tomatoes were selected as the model, and the proposed method was compared with traditional US-assisted disinfection methods (US-10 ppm free chlorine washing + TW rinsing and US-5 ppm chlorine dioxide washing + TW rinsing) to analyze the disinfection efficacy and quality changes. During storage, US-PAA + 1%AA facilitated additional 0.7-0.9, 0.6-0.8, 0.7-1.0, and 0.5-1.0 log CFU/g reductions in the counts of Escherichia coli O157:H7, Salmonella Typhimurium, aerobic mesophilic counts, and molds and yeasts, respectively, as compared with traditional US-assisted methods. Sensory properties, color index, total soluble solids, titratable acidity, and weight loss were not negatively affected by any of the treatments. Firmness was slightly reduced after all treatments; however, the firmness of the samples was maintained during storage, in contrast with the decreased firmness observed in the control. Phenolic content and antioxidant activity significantly increased after all treatments. Further analysis of two key enzymes (phenylalanine ammonia-lyase and 4-coumarate-CoA ligase) involved in phenolic synthesis showed that their levels significantly increased following all treatments, leading to an increase in phenolic content and antioxidant activity. This result also indicated that US-assisted washing could act as an abiotic elicitor to increase nutritional content. Overall, US-PAA + 1%AA treatment served as an effective method for disinfecting produce during washing and for controlling microbial growth after washing without prolonging the processing time, which is an advantage over traditional US-assisted washing.

Prevalence of Multidrug-Resistant Listeria monocytogenes in Dairy Products with Reduction Trials Using Rosmarinic Acid, Ascorbic Acid, Clove, and Thyme Essential Oils

Continuous monitoring of Listeria spp., particularly Listeria monocytogenes, in foods is a mandatory task for food safety and microbiology sectors. This study aimed to determine the prevalence and antimicrobial resistance patterns of L. monocytogenes in milk and dairy products retailed in Egypt. Furthermore, an experimental trial was conducted to investigate the antilisterial effects of some phytochemicals. A total of 200 samples (market raw milk, Kareish cheese, Damietta cheese, and plain yoghurt, 50 each) were collected and examined for detection of Listeria spp. The results revealed that 8, 12, 1, and 0 samples of market raw milk, Damietta cheese, Kareish cheese, and plain yoghurt were contaminated with Listeria spp., respectively. Antimicrobial sensitivity testing revealed that all L. monocytogenes isolates (15) were resistant to streptomycin and erythromycin. Molecular analysis revealed that 86.67% of L. monocytogenes harbored hylA virulent gene. Use of rosmarinic acid, ascorbic acid, thyme, and clove essential oils significantly ( $P<0.05$ ) reduced L. monocytogenes growth in soft cheese—artificially contaminated with L. monocytogenes throughout a 4-week incubation period. In conclusion, strict hygienic conditions should be adopted during the preparation and distribution of dairy products. In addition, rosmarinic acid, ascorbic acid, clove, and thyme essential oils are good candidates as food preservatives with antilisterial activities.