Effect of Yoghourt Starter Culture and Nickel Oxide Nanoparticles on the Activity of Enterotoxigenic Staphylococcus aureus in Domiati Cheese

Domiati cheese is the most popular type of white soft cheese in Egypt. Staphylococcus aureus is a common microorganism that can easily contaminate Domiati cheese during processing and distribution. Enterotoxigenic S. aureus strains produce staphylococcal enterotoxins (SE) that have been involved in food poisoning outbreaks worldwide. The aim of the present study was to examine the inhibitory effect of yoghourt starter culture and nickel oxide nanoparticles (NiO NPs) on the development of the enterotoxigenic S. aureus together with the enterotoxin production during the manufacturing and storage of Domiati cheese. Fresh cow’s milk was inoculated with S. aureus in a count of six log CFU/mL with the addition of either yoghourt starter culture or NiO Nps. The cytotoxicity of NiO NPs on normal human epithelial cells (HEC) was assessed using the MTT assay. In the current study, the inoculated milk was used for making Domiati cheese and the survival Weibull and log-linear models were fitted to the observed data. The obtained results showed that the mean log count of S. aureus decreased one week earlier by using yoghourt starter culture. Staphylococcal enterotoxin A (SEA) was identified only in the control cheese. Notably, Domiati cheese contained MIC of NiO NPs (35 µg/mL), which resulted in a significant decrease in S. aureus counts since at day 21 of cheese ripening it was not detected (<10 CFU/g). Overall, the current study indicated that the addition of yoghourt starter culture and NiO NPs during the processing of Domiati cheese could be useful candidates against S. aureus and enterotoxin production in the dairy industry

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Inhibitory Effect of some Nanomaterials on Streptococcus species Producing Biofilm Isolated from some Dairy Farms

Multidrug resistant, Streptococcus (Strep.) producing biofilm (SPB) considered the most important environmental pathogens associated with concern problems in dairy farms and confers public health hazard. This cohort study aimed to evaluate Strep. spp. in dairy farms, antibiotic resistance pattern against 15 antibiotics, and detected the ability of isolates to biofilm formation phenotypically by quantitative (polystyrene), qualitative (Congo Red Agar (CRA)) and Geno-typically by lmb and brpA genes. The minimum biofilm eradication concentration (MBEC) of chitosan nanoparticles (CNPs) and carvacrol nano-emulsions (CNE) were investigated in vitro by polystyrene method (which is considered the first record, according to the authors knowledge) in field by washing milking utensils. A total of 150 milk samples (cows and buffaloes) were collected, in addition to 48 swabs from milking utensils of different farms in Assiut Governorate, Egypt. The prevalence of Strep. spp. was 21.72% of all examined samples and the most frequently isolated pathogen was Strep. agalactia (12.6 %). Overall, there were 14% of isolates resistant to vancomycin. Strep. uberis revealed the highest resistance to most antibiotics used and 80% of it considered biofilm producers. SPB were classified to strong (23.3%), moderate (32.5%), weak (27.9%) and non-producers (16.3%) by polystyrene method, while, 55.8% considered biofilm producers by CRA. All SPB were positive to lmb and only three were negative to brpA genes. The prepared nanomaterials were characterized by Transmission Electron Microscope (TEM) and the MBECs were 30% and 20 % for CNPs and CNE, respectively. In addition, complete inhibition to SPB in milking utensils occurred at 10 and 20 minutes from washing by CNE 20% and CNPs 30%, respectively. The present study concluded that most of the isolated Strep. spp. are biofilm producers, which are resistant to studied chemotherapeutic agents. CNE is considered more efficient than CNPs for elimination of SPB

Natural approach of using nisin and its nanoform as food bio-preservatives against methicillin resistant Staphylococcus aureus and E.coli O157:H7 in yoghurt

Abstract Background Natural antimicrobial agents such as nisin were used to control the growth of foodborne pathogens in dairy products. The current study aimed to examine the inhibitory effect of pure nisin and nisin nanoparticles (nisin NPs) against methicillin resistant Staphylococcus aureus (MRSA) and E.coli O157:H7 during the manufacturing and storage of yoghurt. Nisin NPs were prepared using new, natural, and safe nano-precipitation method by acetic acid. The prepared NPs were characterized using zeta-sizer and transmission electron microscopy (TEM). In addition, the cytotoxicity of nisin NPs on vero cells was assessed using the 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. The minimum inhibitory concentrations (MICs) of nisin and its nanoparticles were determined using agar well-diffusion method. Further, fresh buffalo’s milk was inoculated with MRSA or E.coli O157:H7 (1 × 106 CFU/ml) with the addition of either nisin or nisin NPs, and then the inoculated milk was used for yoghurt making. The organoleptic properties, pH and bacterial load of the obtained yoghurt were evaluated during storage in comparison to control group. Results The obtained results showed a strong antibacterial activity of nisin NPs (0.125 mg/mL) against MRSA and E.coli O157:H7 in comparison with control and pure nisin groups. Notably, complete eradication of MRSA and E.coli O157:H7 was observed in yoghurt formulated with nisin NPs after 24 h and 5th day of storage, respectively. The shelf life of yoghurt inoculated with nisin nanoparticles was extended than those manufactured without addition of such nanoparticles. Conclusions Overall, the present study indicated that the addition of nisin NPs during processing of yoghurt could be a useful tool for food preservation against MRSA and E.coli O157:H7 in dairy industry