Category Archives: Staphylococcus aureus

Research – The effect of silver nanocomposite packaging based on melt mixing and sol–gel methods on shelf life extension of fresh chicken stored at 4 °C

Wiley Online

Abstract

In the present study, seven types of films were produced using different proportions of polyethylene containing silver, clay, and titanium dioxide nanoparticles. Following the determination of the minimum inhibitory concentration of the films in the eradication of Staphylococcus aureus and Escherichia coli, the film containing 5% silver nanoparticles and 5% titanium dioxide nanoparticles was found to have the highest antimicrobial property and was determined to be an ideal cover for food products. The antibacterial effect of the films on the shelf life extension and quality of the chicken stored at 4 °C in the Days 1, 3, and 5 of the experiment was checked. The structure and morphology of the nanoparticles and the selected films were evaluated using a field emission scanning electron microscope, scanning electron microscope, transmission electron microscope, Fourier‐transform infrared spectroscopy, and dynamic light scattering. The analysis of the results indicated that the most appropriate inhibition growth was observed with S. aureus and E. coli in nutrient agar and the largest diameter of the radial inhibition zone occurred with S. aureus. Moreover, the analysis of variance showed that the effect of different concentrations of silver and titanium dioxide nanoparticles was significant (p < .05). The results of this study showed that the produced nanocomposite was used to preserve chicken meat for 5 days at 4 °C inhibited the growth of both types of bacteria.

Practical applications

Nowadays production of active packaging is increasing worldwide as they were proved to have numerous effects on inhibiting of microbial growth and even bactericidal effects. Therefore, a wide variety of food producers in different sections namely agriculture, dairy, and meat industries have applied nanopackaging using different nanoparticles. Thus, more research on different physicochemical and antimicrobial effects are needed.

Research – Nisin penetration and efficacy against Staphylococcus aureus biofilms under continuous-flow conditions

Microbiology Research

Biofilms may enhance the tolerance of bacterial pathogens to disinfectants, biocides and other stressors by restricting the penetration of antimicrobials into the matrix-enclosed cell aggregates, which contributes to the recalcitrance of biofilm-associated infections. In this work, we performed real-time monitoring of the penetration of nisin into the interior of Staphylococcus aureus biofilms under continuous flow and compared the efficacy of this lantibiotic against planktonic and sessile cells of S. aureus . Biofilms were grown in Center for Disease Control (CDC) reactors and the spatial and temporal effects of nisin action on S. aureus cells were monitored by real-time confocal microscopy. Under continuous flow, nisin caused loss of membrane integrity of sessile cells and reached the bottom of the biofilms within ~20 min of exposure. Viability analysis using propidium iodide staining indicated that nisin was bactericidal against S. aureus biofilm cells. Time-kill assays showed that S. aureus viability reduced 6.71 and 1.64 log c.f.u. ml for homogenized planktonic cells in exponential and stationary phase, respectively. For the homogenized and intact S. aureus CDC biofilms, mean viability decreased 1.25 and 0.50 log c.f.u. ml, respectively. Our results demonstrate the kinetics of biofilm killing by nisin under continuous-flow conditions, and shows that alterations in the physiology of S. aureus cells contribute to variations in sensitivity to the lantibiotic. The approach developed here could be useful to evaluate the antibiofilm efficacy of other bacteriocins either independently or in combination with other antimicrobials.

Research – Antibacterial Effects of Phytic Acid against Foodborne Pathogens and Investigation of Its Mode of Action

Journal of Food Protection

ABSTRACT

This study investigated the antimicrobial mechanism of phytic acid (PA) and its antibacterial effects in combination with ethanol. The MIC of PA on Escherichia coli ATCC 11229, Staphylococcus aureus ATCC 6538P, Bacillus subtilis ATCC 6633, and Salmonella Typhimurium CICC 27483 were 0.24, 0.20, 0.26, and 0.28% (w/w), respectively. E. coli ATCC 11229 and S. aureus ATCC 6538P were selected to investigate the mechanism of PA by analyzing its effects at 1/2MIC and at MIC on the cell morphology, intracellular ATP, and cell membrane integrity. Environmental scanning electron microscope images revealed that PA was able to change the cell morphology and disrupt the intercellular adhesion. PA retarded bacterial growth and caused cell membrane dysfunction, which was accompanied by decreased intracellular ATP concentrations. Flow cytometry analysis further revealed that almost all the bacterial cells were damaged after treatment with PA at its MIC for 2 h. Moreover, PA has a synergistic antimicrobial ability when used in combination with ethanol. These results suggested that PA is effective in inhibiting growth of foodborne pathogens mainly by the mechanism of cell membrane damage and to provide a theoretical basis for the development of natural antimicrobial agents in the food industry.

Research – Antibacterial Effects of Phytic Acid against Foodborne Pathogens and Investigation of Its Mode of Action

Journal of Food Protection

This study investigated the antimicrobial mechanism of phytic acid (PA) and its antibacterial effects in combination with ethanol. The MIC of PA on Escherichia coli ATCC 11229, Staphylococcus aureus ATCC 6538P, Bacillus subtilis ATCC 6633, and Salmonella Typhimurium CICC 27483 were 0.24, 0.20, 0.26, and 0.28% (w/w), respectively. E. coli ATCC 11229 and S. aureus ATCC 6538P were selected to investigate the mechanism of PA by analyzing its effects at 1/2MIC and at MIC on the cell morphology, intracellular ATP, and cell membrane integrity. Environmental scanning electron microscope images revealed that PA was able to change the cell morphology and disrupt the intercellular adhesion. PA retarded bacterial growth and caused cell membrane dysfunction, which was accompanied by decreased intracellular ATP concentrations. Flow cytometry analysis further revealed that almost all the bacterial cells were damaged after treatment with PA at its MIC for 2 h. Moreover, PA has a synergistic antimicrobial ability when used in combination with ethanol. These results suggested that PA is effective in inhibiting growth of foodborne pathogens mainly by the mechanism of cell membrane damage and to provide a theoretical basis for the development of natural antimicrobial agents in the food industry.

Research – An approach to improve the safety and quality of ready‐to‐eat blueberries

Wiley Online

Abstract

Bioactive edible coatings were developed and applied to blueberries as a natural treatment. E. coli O157:H7, L. innocuaS. aureus, and P. aeruginosa were subjected to four bioactive compounds and to three film‐forming solutions (FFS). Vanillin and geraniol at low concentrations (1.2–1.8 mg/mL and 0.4–1 μL/mL) demonstrated significant inhibitory effects on all pathogens counts. Chitosan (Ch) showed a high antimicrobial activity (final counts below 2 log CFU/mL). The effectiveness of Ch plus vanillin (Ch‐Va) and geraniol (Ch‐Ge) in improving the safety were tested against pathogens inoculated on blueberries. Ch, Ch‐Va, and Ch‐Ge coatings exerted a bactericidal effect on all pathogens (from 1.24 to more than 2 log reductions). Significant reduction in yeast and mold counts was achieved with Ch (1.09 log) and Ch + Va (1.74 log). Sensory attributes of blueberries remained acceptable. Ch‐Va and Ch‐Ge were an alternative to improve the quality and safety and could be effective in extending the shelf life of ready‐to‐eat blueberries.

Practical applications

The present study proposes the use of natural coatings enriched with biopreservatives as a technological alternative to enhance the quality and safety of minimally processed fruits. According to the results obtained, the application of chitosan plus vanillin/geraniol coatings on fresh blueberries would allow to offer a safe product and respond the growing demand of consumers for fresh, environmentally friendly and chemical preservatives‐free foods. These findings and those obtained by the sensory evaluation support the practical application of this alternative in the minimally processed fruit industry.

Research – Inactivation of Staphylococcus aureus and Escherichia coli in milk by different processing sequences of ultrasound and heat

Wiley Online

Abstract

Different processing sequences of ultrasound and heat were applied for the inactivation of Staphylococcus aureus and Escherichia coli in milk. The changes in whey protein content, particle size, zeta potential, pH, viscosity, and color values were studied to evaluate the effects on the quality of milk. Results indicated ultrasound treatment (600 W, 5 min) with postheating (63 °C 5 min) reduced S. aureus and E. coli by 1.58 and 2.02 log cfu/ml, respectively, but yielded 0.26 and 0.19 log cfu/ml sublethal S. aureus and E. coli. Milk preheated to 63 °C (5 min) followed by ultrasound (600 W, 5 min) showed 1.17 and 1.68 log reductions for S. aureus and E. coli, respectively, and the sublethal S. aureus and E. coliwere reduced to 0.16 and 0.09 log cfu/ml. The increased cavitation effects make the simultaneous treatment (600 W, 63 °C, 5 min) the most effective approach in killing S. aureus and E. coli, causing 1.67 and 2.16 log reductions, respectively, and producing negligible sublethal bacteria. The simultaneous treatment was also able to improve some physical–chemical properties of milk; smaller particle size and whiter color were achieved. However, whey protein and stability indices of milk were slightly deteriorated by this approach.

Practical applications

In food processing fields, thermosonication can serve as an alternative processing technique to thermal pasteurization. Especially, the simultaneous treatment of ultrasound and heat showed best inactivation effect for viable and sublethal cells, while maintaining the overall milk quality in the meantime. The results of this research may be useful for the treatment of various bacterial contamination and give the guidance for milk processing

Research – Microbial risks in food franchise: A step forward in establishing ideal cleaning and disinfection practices in SSOPs

Wiley Online

Abstract

Microbial contamination in coffee specialty franchises using uniform processing procedures in Korea was examined. Cleaning or disinfection practices for sanitation standard operating procedures (SSOPs) are proposed. For each processing step, food materials and associated processing environments were tested for heterotrophic bacteria (HB), Escherichia coli, coliform, and Staphylococcus aureus. Existing SSOP cleaning or disinfection practices were also evaluated. Ice‐making procedures revealed coliform and HB contamination in all coffee houses, with high HB contamination on several supplementary food materials and associated food utensils. Microbial loads in food materials or final products were high on structures and materials that are difficult to clean and disinfect. Staphylococcus species contaminated food machinery and utensils directly contacted by food handlers. Based on our analysis of cleaning and disinfection practices in each franchise’s SSOPs, current practices should be complemented to ensure food safety. Our results provide a foundation for developing sanitation standards optimized for coffee specialty franchises.

Practical applications

Franchise brands operating collectively require well‐established sanitation practices such as sanitation standard operating procedures (SSOPs) to ensure food safety and quality. Microbiological studies were performed to evaluate coffee processing procedures and environments at specialty franchise brands. Hygiene practices in SSOPs were simultaneously evaluated to examine cleaning and disinfection procedures. In several processing procedures and associated processing environments, coliform and Staphylococcus aureus were detected on food handlers’ hands, gloves, and hand‐accessible areas of food utensils or machinery simultaneously. Coliforms were also detected in edible ice cubes and on related utensils or machinery for ice production or storage (ice‐making machine, ice‐bin). Heterotrophic bacteria (HB) were detected at high densities in sugar syrup (under‐using) and edible ice (during production and storage). Particularly, HB concentrations increased during processing. Thus, microbial contamination is increased by various factors during processing, particularly inappropriate cleaning or disinfection of utensils or machinery. Evaluation of cleaning and disinfection practices for each franchise’s SSOPs revealed that the cleaning and disinfection practices for machinery or utensils accessible to worker’s hands must be supplemented. Establishments serving a wide variety of coffee beverages may require complex and different processing procedures. Because utensils and machinery affecting the microbial load of the final product can vary, the areas and targets of cleaning and disinfection should be expanded. Second, the structure or material characteristics of food utensils or machinery that are difficult to clean and disinfect can lead to microbial growth. Cleaning or disinfection of food utensils or machinery should be considered in SSOPs. Purchasing management (as a major category of SSOPs for food safety) should be expanded to utensils or machinery in addition to food materials. Furthermore, cleaning and disinfection targets aimed at under‐used utensils or facilities must be established in SSOPs.