Comparison of controlling capabilities of lactobionic acid, nisin, and K-Sorbate against dairy-borne Staphylococcus aureus, Escherichia coli, and mold in soft cheese.

Background: The utilization of chemical preservatives holds the promise of effectively controlling microbial growth in soft cheese. Aim: The first trial aimed to compare the effectiveness of lactobionic acid (LBA) and K-Sorbate in controlling the proliferation of Staphylococcus aureus, Escherichia coli, and mold in white soft cheese. The subsequent part of the study explored the inhibitory effects of K-Sorbate, nisin, and LBA on mold populations in cheese whey. Methods: Two sets of soft cheese were produced. One set was contaminated with S. aureus, while the other was with E. coli, each at concentrations of 1 log CFU/ml and 1 log CFU/100 ml. Different concentrations of LBA were incorporated into these sets of cheese. Similar cheese samples were treated with K-Sorbate. For the subsequent part of the study, it was manufactured and divided into groups that inoculated with LBA with different concentrations, K-Sorbate, and nisin. Results: With higher S. aureus inoculation, by day 18, the positive control exhibited growth exceeding 5 log CFU/g. In contrast, the LBA treatment dropped below limit of detection (LOD) and K-Sorbate yielded 4.8 log CFU/g. While with lower S. aureus inoculation, the positive control reached log CFU/g, while LBA treatment fell below LOD by day 14, and K-Sorbate reached 2.9 log CFU/g. For E. coli inoculation, with higher concentrations, by day 18, the positive control exceeded 5 log CFU/g. Conversely, LBA treatment greatly decreased and K-Sorbate treatment measured 5.1 log CFU/g. With lower E. coli concentrations, the positive control surpassed 3 log CFU/g, yet LBA treatment dropped below LOD by day 3. Mold counts indicated some inhibition with the K-Sorbate treatment, while control groups showed growth. LBA treatments exhibit noticeable growth inhibition. About the other part of the study, the outcomes demonstrated that while growth of mold occurred in the control group, inhibitory effects were apparent in the treatment groups, and significant distinctions existed between K-Sorbate, nisin, LBA treatments, and the control group. Conclusion: Our findings suggest that LBA has the potential to effectively control the growth of E. coli, S. aureus, and mold in soft cheese. Moreover, LBA displays greater preservative efficacy compared to K-Sorbate and nisin.

Beneficial effect of probiotics supplementation on quality of edible fresh table eggs during storage.

Background: This study discussed the effect of probiotic supplementation on laying hens' diets and the enhancement of egg quality during the cold storage period. Aim: To study the efficacy of the addition of probiotics to hen diets in terms of improving the egg's quality during the cold storage period and protection against enteric pathogens. Methods: 100 table eggs were collected from farms of laying hens on a battery system, 46 weeks old HylineW36 white in Sharkia Government. The collected eggs were separated into 2 groups (50 each); the control group from hens fed on diets without probiotics, and the probiotic group from hens fed on diets with (100 g/ton) of supplemented probiotics preparation. All groups were separated into 5 sub-groups for the examinations; on the fresh day, 7th, 14th, 21st, and 28th days on cold storage at 4°C. Chemical, physical, and microbiological examinations were done for internal egg contents and eggshells. Results: Our results showed that probiotics supplements have advantageous effects on the quality of eggs during cold storage periods. Also, microbiological examination proved that eggshells from hens fed on diets with probiotics supplemented (100 g/ton) have decreased the level of bacterial contamination with Salmonella and Escherichia coli than hens fed on a regular diet. Conclusion: It could be shown that the probiotics supplementation may decrease and reduce the effect of the storage period on the quality of shell, albumen, and yolk.

Occurrence and D-Tryptophan Application for Controlling the Growth of Multidrug-Resistant Non-O157 Shiga Toxin-Producing Escherichia coli in Dairy Products.

The objectives of the current study were first to determine the prevalence of non O157:H7E. coli, especially Shiga toxin-producing Escherichia coli (STEC) in retailed milk and dairy products in Egypt. Second, the antimicrobial resistance profiling and virulence genes of the isolated E. coli strains were screened. Third, evaluation of the inhibitory effects of D-tryptophan against E. coli O26:H11 was further performed. The results revealed that 20% (30/150) of the samples were STEC positive, with 64 isolates harboring some virulent genes, such as Stx1, Stx2, eaeA, and hylA. Serological identification revealed four different pathotypes belonging to EPEC, ETEC, EHEC, and EIEC. Antimicrobial susceptibility testing revealed that 100%, 98.44%, 92.19%, 71.87%, 65.63% and 64.06% of the isolates had a resistance against tetracycline, oxacillin, erythromycin, nalidixic acid, sulphamethoxazol, and ampicillin, respectively. D-tryptophan addition (40 mM) to E. coli O26:H11-inoculated soft cheese and ice cream revealed a significant reduction (p < 0.05) in bacterial growth, especially when accompanied with other food stressors. D-Tryptophan is considered as an effective food preservative and as a promising alternative candidate in the dairy industry.

Assessment of a regulatory sanitization process in Egyptian dairy plants in regard to the adherence of some food-borne pathogens and their biofilms.

Food-borne pathogens may develop certain strategies that enable them to defy harsh conditions such as chemical sanitization. Biofilm formation represents a prominent one among those adopted strategies, by which food-borne pathogens protect themselves against external threats. Thus, bacterial biofilm is considered as a major hazard for safe food production. This study was designed to investigate the adherence and the biofilm formation ability of some food-borne pathogens on stainless steel and polypropylene surfaces using chip assay, and to validate regular sanitizing process (sodium hypochlorite 250 mg/L) for effective elimination of those pathogens. Sixteen pathogenic bacterial strains, previously isolated from raw milk and dairy products at Zagazig city, Egypt (9 Staphylococcus aureus, 4 Cronobacter sakazakii and 3 Salmonella enterica serovar Typhimurium), were chosen for this study. Strains showed different patterns of adherence and biofilm formation on tested surfaces with minor significance between surfaces. The ability of sodium hypochlorite to completely eradicate either adhered or biofilm-embedded pathogens varied significantly depending on the strain and type of surface used. Whilst, sodium hypochlorite reduced tested pathogens counts per cm² of produced biofilms, but it was not able to entirely eliminate neither them nor adherent Cronobacter sakazakii to stainless steel surface. This study revealed that biofilm is considered as a sustainable source of contamination of dairy products with these pathogens, and also emphasized the need of paying more attention to the cleaning and sanitizing processes of food contact surfaces.

In vitro inhibition of expression of virulence genes responsible for colonization and systemic spread of enteric pathogens using Bifidobacterium bifidum secreted molecules.

Enteric pathogens such as Salmonella enterica serovar Typhimurium and Enterohaemorrhagic Escherichia coli require an initial indispensable step of attachment or invasion of enterocytes before they can produce systemic disease and translocate to their target organs. Prevention of either of these steps will result in an avirulent state and limit their pathogenicity. In vitro tests demonstrated that molecules secreted by Bifidobacterium bifidum interfere with both attachment and invasion. The main regulatory genes controlling the virulence factors essential for these pathogenicity steps were efficiently down-regulated when treated with chromatographically separated B. bifidum cell free fractions as measured by reporter constructs and confirmed by RT-PCR. Moreover, the ability of both pathogens to colonize eukaryotic cells was significantly reduced, and the capacity of Salmonella to survive and multiply within macrophages was also diminished upon treatment with these bioactive molecules. These results indicate that probiotic Bifidobacteria strains may represent an effective alternative approach to control food-borne enteric pathogens.

Probiotics down-regulate genes in Salmonella enterica serovar typhimurium pathogenicity islands 1 and 2.

Salmonella Typhimurium pathogenesis relies mainly on the expression of genes of two pathogenicity islands, Salmonella pathogenicity islands 1 and 2 (SPI1 and SPI2). Each island has its own pattern of expression and regulation. Success in suppression of the responsible key activator of each island would be an effective way of controlling Salmonella, especially with the emerging problem of antibiotic-resistant strains. Probiotics have been shown to inhibit several foodborne pathogens, and their mode of action may partly involve down-regulation of virulence genes. To investigate whether probiotics played a role in the regulation of the pathogenicity islands SPI1 and SPI2 in Salmonella, two reporter strains were constructed in which the general regulator of SPI1, hilA, and the response regulator of SPI2, ssrB, were fused with luxCDABE genes. These constructs were used to screen the effect of probiotics on the expression of each gene. Molecules secreted by Bifidobacterium bifidum were able to down-regulate both genes.