Inactivation of food poisoning bacteria and Geobacillus stearothermophilus spores by high pressure carbon dioxide treatment

Inactivation of the vegetative foodborne pathogens by high pressure carbon dioxide treatment (HPCT) was investigated. Pseudomonas aeruginosa IFO3445, Aeromonas hydrophila IFO13286, Salmonella enteritidis JCM3313, Salmonella typhimurium IID1000, Yersinia enterocolitica JCM1677, Escherichia coli O157:H7 ATCC35150, E. coli O157:H7 ATCC43889, Staphylococcus aureus FDA209P and Listeria monocytogenes 1/2a were used in this study. In all cases, HPCT at 35 °C, 10 MPa for 1 min reduced initial numbers by approximately 6 logs. In addition HPCT inactivation of 9 pathogenic strains of Bacillus cereus (mixture of spores and vegetative cells) was investigated. HPCT at 75 °C, 10 MPa for 120 min resulted in significant inactivation in all the strains. The effect of HPCT (30 MPa at 95 °C for up to 120 min) on the inactivation of Geobacillus stearothermophilus spores in the presence of sodium chloride (3% and 6% w/v), glucose (6% and 12% w/v) and ethanol (10% and 20% v/v) was also studied. Both sodium chloride and glucose had a protective effect and the level of inactivation was reduced. The effect was in proportion to the solute concentration. However, 10% and 20% ethanol did not significantly affect the level of inactivation.     

Quantification and variability of Escherichia coli and Staphylococcus aureus cross-contamination during serving and consumption of cooked thick porridge in Lungwena rural households, Malawi

The study investigated bacterial transfer to cooked thick porridge via ladles and hands during serving in 29 households in Lungwena, rural Malawi. Household stored water used for hand and ladle washing, was contaminated with Escherichia coli and Staphylococcus. aureus from hands of members of the household or from contaminated ladles used in food preparation. The results showed that hands became contaminated with E. coli and S. aureus cells in the range 0.6–3.7 and 2.2–4.3 log₁₀ CFU/cm², respectively, following washing with the contaminated water. Ladles became contaminated with 0.9–3.2 log₁₀ CFU/cm² of E. coli cells whereas contamination with S. aureus on ladles ranged between 1.9 and 4.6 log₁₀ CFU/cm². Bacterial transfer from hands to food ranged from <1 to 3.6 log₁₀ CFU/g for E. coli and 2.1 to 4.2 log₁₀ CFU/g for S. aureus. Ladle surfaces transferred from 1.3 to 3.1 and from 1.2 to 4.3 log₁₀ CFU/g of E. coli and S. aureus, respectively, on to the food. Contamination of food by hands was significantly (p < 0.05) higher than that of ladles and transfer of S. aureus was significantly (p < 0.05) higher than that of E. coli. The amount of bacteria transferred to the recipient depended on the wash water type and bacteria type. The study has demonstrated that although the traditional cooking of thick porridge inactivates S. aureus and E. coli, the porridge can be contaminated with bacteria during consumption using hands and serving on to a plate with wooden ladles.     

Efficacy of ozone to reduce microbial populations in date fruits

Ozone is strong oxidant and potent disinfecting agent. There are numerous application areas of ozone in food industry such as sanitation of food plant equipments, surface hygiene and reuse of waste water. While the application of ozone for dried fruits disinfection and for fresh fruits and vegetables microflora destruction has been studied extensively, relatively little information is available on the potential of ozone to reduce microbial populations in date fruits. In this study, ozone was applied in gas form at three concentrations (1, 3, and 5 ppm) for four different periods (15, 30, 45 and 60 min) on Iranian date fruits and the reduction in the total bacterial count, Coliform, Staphylococcus aureus as well as yeast/mold counts were examined. The promising results indicated the efficacy of ozone to reduce the microbial populations in date fruits. Escherichia coli and S. aureus were not found on cultured plates inoculated with the treated samples after treatment with 5 ppm (p < 0.05) in 60 min. The method of ozone generation, type of application, as well as the optimal exposure time and concentration of ozone as an antimicrobial agent in date fruit is mentioned in detail.     

Disinfection of selected vegetables under nonthermal treatments: Chlorine,acid citric,ultraviolet light and ozone

Lettuce, tomatoes and carrots were evaluated under four disinfection methods. Chlorine (50, 100 and 200 ppm) was compared for effectiveness with citric acid (0.5, 1 and 1.5%), ultraviolet light (UV-C) (0.65 and 1.6 mW/cm²) and ozone (5 ppm) to inactivate Escherichia coli ATCC 11775. Processing times were from 3 min up to 60 min. Hunter color parameters, color functions (ΔE, hue, chroma), tomato color index (TCI) and whiteness index (WI) were evaluated after disinfection. Results showed that citric acid was not effective for inactivation of E. coli at the tested conditions. UV-C was effective in the inactivation of the microorganism when fluence was higher, being more effective in the smooth surface of tomato (2.7 log). Meanwhile, ozone was also able to inactivate bacteria in tomatoes (2.2 log) after only 3 min. Carrots and lettuce showed lower inactivation for all treatments because of their porous and roughened surfaces. UV-C was the treatment that most affected the color of the produce; it generated browning of lettuce, and increase of TCI and WI of carrots. Ozone also affected the greenness of lettuce. Concentration, dose and processing times of novel disinfection methods need to be evaluated not only for microbial counts, but also sensory properties.     

Inactivation of Salmonella spp. in ground chicken using high pressure processing

High Pressure Processing (HPP) is a safe and effective process for improving the microbial safety and shelf-life of foods. Salmonella is a common contaminant in poultry meat and is frequently responsible for foodborne illness associated with contaminated poultry meat. In this study the inactivation of a five-isolate cocktail of Salmonella spp. in ground chicken (95% lean) using HPP at refrigeration temperature (4–6 °C) was studied. More than 5-log CFU/g inactivation was achieved at 450 MPa for10 min. In contrast, HPP treatment at 250 MPa or 350 MPa (single-cycle, 15 min) inactivated 0.5 log or 1.7 log CFU/g, respectively. The multiple-cycle HPP mode at 250 or 350 MPa (3-cycle with 5 min/cycle) showed higher cell reduction at 1.3 or 3.3 log CFU/g, respectively. HPP at 550 MPa for 10 min may reduce the cell counts, initially at 8.5 log CFU/g, to below the detection limit (1.0 log CFU/g) in current study. The images (electron microscopy) of the HPP shocked cells were examined for structural damage, which demonstrated that Salmonella cells may still look intact (with damages on rough/irregular surface at 450 MPa stress) under Scanning Electron Microscopy (SEM), but have significant damage internally (voids and uneven mass distribution patterns) under Transmission Electron Microscopy (TEM).     

Moisture, sawdust, and bleach regulate the persistence of Escherichia coli O157:H7 on floor surfaces in butcher shops

Survival of Escherichia coli O157:H7 on typical butcher shop ceramic floor tiles contaminated with meat juice was compared in the presence and absence of sawdust, and under different moisture and cleaning regimes. Floor tiles from a butcher shop were cut into 5 × 5 cm pieces, and half were cleaned with commercial bleach diluted with water at 60 °C to simulate mopping. A coating of commercial sawdust was applied to half of the tiles, while the other half were left bare. Meat juice collected from beef joints was inoculated with E. coli O157:H7 (strain #3704), and subsequently applied onto tiles at a density of 6.47 log₁₀ CFU cm⁻². Thereafter, tiles were stored at room temperature (20 ± 2 °C), with half maintained under moist conditions [relative humidity (RH) close to 100%] and the other half gradually air-dried (RH 70 ± 5%). Viable E. coli O157:H7 persisted on all tiles over 72 h, although die-off rate varied with environmental conditions. Desiccation of surfaces resulted in a more rapid decline in E. coli O157:H7 numbers, while cleaning of the tiles with bleach prior to contaminating also affected pathogen recovery. Overall, greater numbers of cells were recovered from tiles when no sawdust had been applied; however the presence of sawdust only reduced survival on tiles under dry conditions, and damp sawdust actually increased survival. This highlights the importance of regular cleaning and removal of sawdust to reduce pathogen persistence.     

Evaluation of electrolyzed water as cleaning and disinfection agent on stainless steel as a model surface in the dairy industry

In the dairy industry, cleaning and disinfection of surfaces are important issues and development of innovative strategies may improve food safety. This study was aimed to optimize the combined effect of alkaline electrolyzed water (AEW) and neutral electrolyzed water (NEW) as alternative cleaning and disinfection procedure on stainless steel plates (SSP) with and without electropolishing. NEW at 10 ppm total available chlorine (TAC), achieved a ˃5 log CFU/mL reduction of milk spoilage bacterial suspension, grown in trypticase soy broth (8.7 log CFU/mL of each bacterial strain: Pseudomonas aeruginosa, Enterococcus faecalis and Micrococcus luteus) contacted for 30 s. An optimal design of experiments was used to assess the combined effect of cleaning with AEW, followed by disinfection with NEW (40 ppm TAC, contact time 3 min). Tested factors were contact time (10, 20 and 30 min), concentration of AEW (100, 200 and 300 mg NaOH/L), temperature (30, 40 and 50 °C), and surface type (304-2B SSP with or without electropolishing), using sixteen treatments with two replicates. The response variable was bacterial cells removal (log CFU/cm²). All main effects, two factors interactions and a quadratic term significantly influenced cells removal, and were modeled using a second order polynomial. Best cleaning procedures were significantly affected by surface roughness; electropolished SSP required 10 min, 100 mg/L AEW at 30 °C, whereas SSP without modification required 30 min, 300 mg/L AEW at 30 °C. From confirmatory tests cells removed were 3.90 ± 0.25 log CFU/cm² for electropolished SSP, and 3.20 ± 0.20 log CFU/cm² for SSP without modification. NEW is non-corrosive, and can be advantageously used for environmentally friendly cleaning and disinfection processes.     

Glycerol monocaprate (monocaprin) reduces contamination by Escherichia coli and Salmonella enteritidis on hard surfaces

Emulsions of glycerol monocaprate (monocaprin) kill a variety of pathogenic bacteria and viruses in suspension. In this study the microbicidal activity of monocaprin against enterobacteria was tested on contaminated hard surfaces. Surfaces were contaminated with nutrient broth or meat juice containing large numbers of Escherichia coli or Salmonella enteritidis. They were then treated with acidified monocaprin emulsions and the surviving bacteria counted. Monocaprin killed S. enteritidis in chicken meat juice on plastic cutting boards and reduced the number of viable E. coli and S. enteritidis by more than 5 log₁₀ in 2 min on a laminated plastic kitchen counter contaminated with nutrient broth. Monocaprin rapidly killed E. coli on glass, stainless steel, laminated plastic, glazed ceramic tiles and polypropylene boards. It was most effective on glass and stainless steel and more effective on dry than on wet surfaces. It was concluded that acidified monocaprin emulsions reduce contamination by pathogenic enterobacteria on hard surfaces. They may be useful as sanitizers in the home, and possibly in public places, where contaminated surfaces are a potential source of transmission of pathogens to humans. Cleaning with monocaprin emulsions may therefore be a means to improve hygiene and infection control.     

Inactivation of Staphylococcus saprophyticus in chicken meat and purge using thermal processing,high pressure processing,gamma radiation,and ultraviolet light (254 nm)

Staphylococcus saprophyticus is a common contaminant in meat and poultry, and causes urinary tract infections after colonization of the gastrointestinal tract, followed by accidental transfer of contaminated feces to the urethra. There is limited information regarding the inactivation kinetics of S. saprophyticus in meat and poultry. When S. saprophyticus was suspended in ground chicken meat (GCM) the thermal processing D₁₀ was 6.26, 0.60 and 0.09 min at 55, 60 and 65 °C, respectively. When S. saprophyticus was inoculated into GCM and subjected to high pressure processing (5 °C, 0–25 min) at 200, 300 or 400 MPa the HPP D₁₀ was 15.5, 9.43, and 3.54 min, respectively. When the S. saprophyticus cocktail was inoculated into GCM and irradiated (5 and −20 °C) the gamma radiation D₁₀ were 0.64 and 0.77 kGy, respectively. When S. saprophyticus was inoculated into chicken purge which was then placed on food contact surfaces including stainless steel, and high density polyethylene and polypropylene and treated with UV-C (0–60 mJ/cm²) the UV-C D₁₀ ranged from 14.9 to 18.5 mJ/cm². These results indicate the inactivation kinetics for S. saprophyticus are consistent with those for other foodborne pathogens and could be controlled in poultry meat and purge without difficulty.     

Removal of Listeria monocytogenes, Staphylococcus aureus and Escherichia coli O157:H7 biofilms on stainless steel using scallop shell powder

Biofilms on steel surfaces containing Listeria monocytogenes, Staphylococcus aureus and Escherichia coli O157:H7 continue to threaten dairy and meat processors. In this study, the ability of scallop shell powder (SSP) to remove biofilms formed by these three pathogens on stainless steel plates was examined. Whey powder solution (WPS) and bench wash water (BWW) provided by dairy and meat factories, respectively, were inoculated with L. monocytogenes, S. aureus or E. coli O157:H7 (9 log₁₀ CFU/ml). Stainless steel plates (10 cm²) were placed in the inoculated fluids and incubated at 20 °C at 48 h to form biofilms. After drying and washing in sterile water, the plates were treated with 0.0, 0.25, or 0.50% (w/v) SSP slurries for 1, 5, or 10 min and then quantitatively examined for the three pathogens. Both 0.25 and 0.50% SSP reduced L. monocytogenes on the plates by 4 log CFU/cm² with a 1 min exposure to 0.50% SSP decreasing S. aureus by 5 logs CFU/cm². After 1 min in 0.25 and 0.50% SSP, E. coli O157:H7 populations in WPS and BWW biofilms decreased 4 and 6 log CFU/cm² and 3 and 5 log CFU/cm², respectively. Increasing the concentration of SSP led to significantly increased efficacy against the tested pathogens (P < 0.05). In conclusion, this study showed that SSP slurries could significantly reduce the numbers of L. monocytogenes, S. aureus and E. coli O157:H7 in biofilms on stainless steel surfaces.     

Distribution of microflora on cattle hides and its transmission to meat via direct contact

In the study, total numbers and distribution of hide microflora, as well as its transferability to meat via direct contact, were investigated. Average total viable counts of bacteria (TVC) and Enterobacteriaceae counts (EC) on 40 bovine hides (cattle from three geographic regions; slaughtered at single abattoir) were 6.7 and 4.3 log cfu/cm², respectively. All hides contained generic Escherichia coli (GEC) but Salmonella spp. was not isolated from any bovine hide examined. Distal leg (metacarpus) and brisket areas were contaminated significantly heavier, in terms of TVC (6.9 and 7.1 log cfu/cm², respectively), EC (4.5 and 4.3 log cfu/cm², respectively) and GEC (occurrence 75% and 65%, respectively), than rump, flank and neck areas. No statistically significant differences in TVC, EC and GEC between the top layer and the lower layer (closer to skin) of the hide hair on visually clean hides were found. Only a small proportion (between 0.5 and 0.00002%) of total microflora (TVC) of hide was transmitted onto meat via direct contact under applied contact conditions (0.5–2 kg for 2 s; stationary or “sliding” contact). Nevertheless, the associated meat safety risks are assessed as significant, due to both high microbial loads existing on hide and high frequency of the hide-origin carcass cross contamination occurring in practice.     

Tenacity of Bacillus cereus and Staphylococcus aureus in dried spices and herbs

Numerous studies examined the antimicrobial effects of spice and herb extracts, whereas little is known about the effects of dry condiments on the survival of microorganisms. This study investigated the impact of dried condiments on the survival of Bacillus cereus and B. thuringiensis spores as well as Staphylococcus aureus cells. In addition, the survival variability between different strains was evaluated. Condiments (allspice, basil, cinnamon, nutmeg, oregano, paprika, parsley and pepper) were artificially contaminated by a dry spiking method using sand as carrier matrix and as control. The results show that counts of B. cereus and B. thuringiensis spores (initial spore count 5.6 ± 0.2 log₁₀ cfu/g and 6.7 ± 0.1 log₁₀ cfu/g, respectively) did not decline significantly in all condiments over a period of 50 weeks. In contrast, in some of the spiked test materials, cell counts of S. aureus (initial cell count 8.1 ± 0.5 log₁₀ cfu/g) were reduced below the detection limit of 10 cfu/g within 10 weeks of storage. D values for S. aureus ranged between 5 and 31 days depending on the strain, condiment and initial contamination level. In conclusion, dried condiments may not affect the survival of spores but can significantly affect the survival of non-spore forming bacteria. As strain variability can occur, tenacity studies should be conducted including a variety of strains.     

Plantaricin MG active against Gram-negative bacteria produced by Lactobacillus plantarum KLDS1.0391 isolated from “Jiaoke”, a traditional fermented cream from China

A bacteriocin named plantaricin MG produced by Lactobacillus plantarum KLDS1.0391 which was isolated from “Jiaoke”, a traditional, naturally fermented cream from Inner Mongolia in China is reported in this article. Plantaricin MG was purified by ammonium sulfate precipitation followed by sequential gel filtration chromatography and reverse-phase chromatography. Mass spectrometry analysis showed the mass of plantaricin MG to be approximately 2180 Da. The bacteriocin showed a broad inhibitory activity against Gram-positive and Gram-negative bacteria including Listeria monocytogenes, Staphylococcus aureus, Salmonella typhimurium and Escherichia coli. The bacteriocin was extremely heat-stable (30 min at 121 °C) and remained active after incubation at pH 2.0–10.0. It was found to be sensitive to proteolytic enzymes (pepsin, trypsin, papain, α-chymotrypsin, proteinase K, Neutrase and Alcalase). The mode of action of plantaricin MG was identified as bactericidal.     

Disinfectant action of Cymbopogon sp. essential oils in different phases of biofilm formation by Listeria monocytogenes on stainless steel surface

Disinfectant solutions based on the essential oils of Cymbopogon citratus (D.C.) Stapf. and Cymbopogon nardus (L.) Rendle, applied alone or in combination, and a control disinfectant solution were tested in two phases (3 and 240 h) of biofilm formation by Listeria monocytogenes ATCC 19117 on AISI 304 (#4) stainless steel surface. Disinfectant solutions based on essential oils have effectively reduced the number of surface-adhered cells, especially after 60 min of contact. The disinfectant solutions based on a combination of essential oils were capable of reducing 100% (5.64 Log CFU cm⁻²) the number of surface-adhered cells after 60 min of contact, at 240 h of biofilm formation. Essential oils of C. citratus and C. nardus, alone or in combination, are new alternatives for disinfection of industrial stainless steel surfaces contaminated by L. monocytogenes.     

An assessment of L. monocytogenes transfer from wooden ripening shelves to cheeses: Comparison with glass and plastic surfaces

Food contact surfaces are subject to contamination by pathogens, which can lead to cross-contamination by transfer to other food products. However, the European regulation specifies that materials intended for safe food contact must not interfere with foodstuff characteristics. Considered a traditional and natural material, wooden boards are used as a “technological tool” during the cheese-ripening process. In France, wood is authorized for food-contact.The aim of this study was to determine the behavior of deliberately contaminated wooden surfaces in direct contact with foodstuffs. The model studied consisted of spruce ripening shelves experimentally inoculated with a well-known potential hazard throughout the production chain of some dairy products: Listeria monocytogenes. Then, the transfer from deliberately inoculated wood to cheese was analyzed and compared with plastic and glass inoculated surfaces.For this purpose, a protocol was developed and first-use spruce boards were inoculated with L. monocytogenes solution at a concentration of 10⁵ CFU/cm² then the microbial transfer to pressed non-cooked cheeses was studied. Factors such as cheese contact time, wood and cheese moisture contents, were tested. We compared the transfer rate with glass plates and plastic sheets with inclined meshes, commonly used throughout the cheese production chain, in the same conditions.The results showed a transfer yield below 3% (CFU/cm²) in the first hour of contact for all surfaces tested and was 0.55% for the wooden boards. No differences were found for drier cheeses or for higher wood moisture content. The wooden porous surface in contact with cheeses was not a factor that increased the L. monocytogenes direct transfer rates. In conclusion, wooden shelves have the lowest transfer rate of L. monocytogenes to pressed non-cooked cheeses compared to glass and polypropylene surfaces. This results contribute to the suitability of use of wooden material for direct contact with food.     

The sanitizing action of essential oil-based solutions against Salmonella enterica serotype Enteritidis S64 biofilm formation on AISI 304 stainless steel

Bacterial adhesion and biofilm formation by Salmonella enterica serovar Enteritidis is a serious concern in the food processing industry; organism persistence in biofilms represents a continual source of contamination. Due to unsuccessful disinfection processes and emerging resistance, conventional control methods are rapidly becoming ineffective, necessitating the development of new control strategies. The following study evaluated the anti-biofilm effect of disinfectant solutions formulated with essential oils (EOs) of peppermint (Mentha piperita) and lemongrass (Cymbopogon citratus) against biofilm formation by S. enterica serotype Enteritidis S64 on stainless steel surface AISI 304 (#4) after 10, 20 and 40 min of contact. A minimum inhibitory concentration (MIC) of 7.8 μL/mL was found for both EOs and disinfectant solutions were formulated based on these MIC values. Ten minutes of sanitizing solution contact significantly reduced (p ≤ 0.05) adhered bacterial populations for both EOs tested. After 20 and 40 min of treatment, cell counts were not detected. Thus, M. piperita and C. citratus EOs can be considered convenient, quality alternatives to the application of conventional sanitizing agents in the food industry; further, use of these EOs addresses the increasing consumer demand for natural products.     

Survival of Listeria innocua and Listeria monocytogenes in muscle of cod (Gadus morhua L.) during salt-curing and growth during chilled storage of rehydrated product

The aim of this work was to study survival of Listeria innocua and Listeria monocytogenes in muscle of cod during salt-curing and growth during chilled storage of the rehydrated product. Fresh cod was inoculated with L. innocua and L. monocytogenes at different levels before salt-curing. After salt-curing and rehydration, the levels were within 1 log₁₀ CFU/g lower than prior to salt-curing in all experiments. During the first 5 days of storage after rehydration, growth of L. innocua was observed in 1 out of 5 experiments at 4 °C, but a 10–100-fold increase were observed in all experiments from day 5 to day 10. The growth started earlier and was more rapid when samples were stored at 7 °C. Growth of L. monocytogenes at 4 °C appeared to start earlier than for L. innocua, but a 10–100-fold increase was observed also for this bacterium. The lag phases in rehydrated products were longer than in experiments with cod muscle juice. The differences could be explained by a different level of salt stress. This work demonstrates that long term exposure to very high salt concentrations does not eliminate Listeria spp., and that Listeria being present in the fish prior to salt-curing can recover and grow in rehydrated salt-cured cod during chilled storage.     

Autochthonous yeasts as potential biocontrol agents in dry-cured meat products

This work aimed to evaluate the ability of selected yeasts, previously isolated from dry-cured hams, to compete with Penicillium nordicum and to inhibit ochratoxin A (OTA) accumulation in a dry-cured pork meat model system in the perspective of their use as surface starter cultures. Two strains of Debaryomyces hansenii and one strain of Hyphopichia burtonii were used. A dry-cured pork meat model system was prepared using meat portions at 0.88 and 0.92 a_w; meat surface disinfection (disinfected or non disinfected) was considered to take into account the possible role of naturally occurring microbial population. P. nordicum (10⁵ spores/ml) was co-inoculated with each yeast strain (around 10⁶ cells/cm² on meat surface) one at a time. Meat portions were incubated in the dark at 18 °C for 30 days. The co-inoculation of P. nordicum and yeasts allowed a decrease in penicillia counts between 1 and 3 Log compared to the control, irrespective of the investigated conditions. Ochratoxin A content in meat portions was significantly reduced when yeasts were co-inoculated with P. nordicum. D. hansenii 147 showed the greatest antagonistic activity and proved to be effective in the investigated conditions. This strain is supposed to be appropriate for typical flavour development, being native to the production plants. Therefore, it is eligible to be tested as biocontrol agent in the dry-cured meat production chain.     

Disinfection efficacy and mechanism of slightly acidic electrolyzed water on Staphylococcus aureus in pure culture

Slightly acidic electrolyzed water (SAEW), considered as a broad-spectrum and high-performance bactericide are increasingly applied in the food industry. However, its disinfection mechanism has not been completely elucidated. This study aims to examine the disinfection efficacy and mechanism of SAEW on Staphylococcus aureus, compared with that of sodium hypochlorite (NaClO) and hydrochloric acid (HCl). SAEW treatment significantly reduced S. aureus by 5.8 log CFU/mL in 1 min, while 3.26 and 2.73 log reductions were obtained with NaClO and HCl treatments, respectively. A series of biological changes including intracellular potassium leakage, TTC-dehydrogenase relative activity and bacterial ultrastructure destruction were studied following disinfection treatment of S. aureus. The results showed that SAEW decreased the relative activity of TTC-dehydrogenase by 65.84%. Comparing intracellular potassium leakage, the SAEW treatment caused a greater percent of protein leakage (108.34%) than the NaClO (18.75%) or HCl (0.84%) treatments. These results demonstrated the potent impact SAEW had on the permeability of cell membranes. In addition, the ranking of partly agglutinated cellular inclusion formation was HCl > SAEW > NaClO. It appeared that HCl, along with its low pH value, are responsible for most of the cytoplasmic disruptions. Overall, this study demonstrated that the disinfection mechanism of SAEW was disrupting the permeability of cell membrane and the cytoplasmic ultrastructures in S. aureus cells.     

Influence of food soiling matrix on cleaning and disinfection efficiency on surface attached Listeria monocytogenes

Cleaning and disinfection are essential steps in preventing contamination of foods with pathogenic and spoilage bacteria. The efficacy of cleaning and disinfection products differ depending on target bacteria and type of soiling. We evaluated the effectiveness of cleaning and disinfecting products against Listeria monocytogenes attached on food soiled inert surfaces in a laboratory model. The number of bacteria on surfaces before and after treatment was quantified using indirect conductometric measurements. L. monocytogenes attached to stainless steel surfaces in fish broth systems reached approx. 10⁴ CFU/cm². However, all cleaning and disinfection products were equally effective in this system since all bacteria were removed or killed. When the steel disks were immersed in a fish or meat emulsions, a level of approx. 10⁵–10⁶ L. monocytogenes per cm² was reached after 2–3 days at 20 °C. In this case, 2–3 log were removed or killed by alkaline cleaning products (MC103 or FC140). Direct use of a peracetic acid based disinfectant (Oxivit Active Plus) killed all bacteria when attached in salmon emulsions, whereas only 1–2 log were removed or killed in the meat emulsion system. Thus, the efficiency of cleaning and disinfection products against L. monocytogenes is strongly influenced by the food matrix.