Surface physiological changes induced by lactic acid on pathogens in consideration of pKa and pH

Antimicrobials affected the surface characteristics and membrane integrity of bacterial cells. The objective of this study was to investigate the physiological changes on the surface of Salmonella Enteritidis (ATCC 14028), Escherichia coli (CGMCC 1.2385), and Listeria monocytogenes (ATCC 19115) induced by lactic acid. Lactic acid was more effective than hydrochloric acid (HCl) at the same pH in inhibiting the growth of these pathogens. The results of zeta potential indicated that surface charges of three pathogens were significantly disturbed by lactic acid treatment. After exposure to 0.5% lactic acid, a rough cell surface with discrete ridges and concave collapses were observed by scanning electron microscopy (SEM). Meanwhile, the release of intracellular potassium (K⁺) also suggested the damage of cytoplasmic membrane. As an effective antimicrobial, lactic acid led to leakage of intracellular K⁺, damage of membrane permeability and integrity, and changes of surface charge in the pathogens.     

Antibacterial characteristics and mechanisms of ɛ-poly-lysine against Escherichia coli and Staphylococcus aureus

The aim of this study was to investigate the antibacterial characteristics and antibacterial mechanisms of ɛ-poly-lysine against Escherichia coli and Staphylococcus aureus. The diameters of inhibition zones of E. coli (10 ± 0.5 mm) and S. aureus (12 ± 0.1 mm) treated by 200 μg/ml ɛ-poly-lysine were much larger than control (5 ± 0.3 mm) (p < 0.05). Minimum inhibition concentration of ɛ-poly-lysine against E. coli and S. aureus was 12.5 μg/ml. Scanning electron microscopy showed that ɛ-poly-lysine damaged the morphology of tested bacterial cells. The increase in electric conductivity of bacterial cells suspension indicated that the cytoplasmic membranes were broken by ɛ-poly-lysine, which caused leakage of ions in cells. SDS-PAGE of bacterial proteins demonstrated that ɛ-poly-lysine could damage bacterial cells through the destruction of cellular proteins. These results indicated that ɛ-poly-lysine has good potential to be as a natural food preservative.     

Effect of organic acids on the photodynamic inactivation of selected foodborne pathogens using 461 nm LEDs

Light emitting diodes (LEDs) are known to inactivate foodborne pathogens. However, the effect of food acidulants on the antibacterial effect of LEDs is unknown. In this study, the influence of organic acids on the photodynamic inactivation of four foodborne pathogens (Escherichia coli O157:H7, Salmonella Typhimurium, Listeria monocytogenes and Staphylococcus aureus) by blue LEDs was investigated. Each pathogen was illuminated by 10-W 461 nm LEDs (22.1 mW/cm²) at 15 °C for 7.5 h in tryptone soya broth of pH 4.5 adjusted with citric, lactic or malic acids. The total energy dosage imparted by the LEDs over the course of the illumination was 596.7 J/cm². Our results showed that at the same pH, the nature of the acids significantly influenced the bacterial inactivation due to the LEDs, irrespective of the bacterial strain. Lactic acid was found to be the most effective in aiding the photodynamic inactivation of the pathogens, followed by citric and malic acids. The reparameterized Gompertz equation was fitted to the inactivation curves to determine the lag phase duration (λ) and the maximum inactivation rate (μ_max) under each condition. The λ values for E. coli O157:H7, S. Typhimurium, L. monocytogenes and S. aureus with lactic acid were 3.68, 3.29, 2.25 and 2.27 h, respectively. The corresponding μ_max values were 1.46, 1.31, 1.07 and 1.21 log CFU/h. The combination of organic acids and LEDs also caused significant sublethal injury to the bacterial cultures with trends similar to those of the inactivation tests. This study showed that food acidulants greatly enhanced the antibacterial effect of LEDs, suggesting the potential of LEDs in preserving acidic foods.     

Photodynamic inactivation of Salmonella enterica Enteritidis by 405 ± 5-nm light-emitting diode and its application to control salmonellosis on cooked chicken

A 405 ± 5-nm LED illumination was evaluated for its antibacterial effect against Salmonella Enteritidis in phosphate buffered saline (PBS) and on the surface of cooked chicken. Its antibacterial mechanism was also elucidated by determining the injury of cellular components using metabolic inhibitors. LED illuminated three S. Enteritidis strains in PBS at doses as high as 0.45 kJ/cm² (for 7.5 h) and on cooked chicken at doses of 1.58–3.80 kJ/cm² (for 20–48 h) at 4, 10, and 20 °C. Results showed that illumination inactivated 1.4–2.1 log CFU/ml of populations in PBS at 0.45 kJ/cm², indicating that S. Enteritidis 130 was more susceptible to illumination than 124 and 125 strains. At 4 °C, Salmonella populations on illuminated cooked chicken decreased by 0.8–0.9 log CFU/cm² at 3.80 kJ/cm², whereas bacterial growth inhibition and delay were observed by illumination at 10 and 20 °C, respectively, regardless of bacterial strain. These results indicate that illumination temperature significantly (P ≤ 0.05) influenced the antibacterial effect of LED on cooked chicken. LED illumination at 4 °C resulted in the incapability of Salmonella cells to repair cellular damage related to metabolism of DNA, RNA, protein, and cell wall. These results suggest that 405 ± 5-nm LEDs under refrigeration conditions could control Salmonella linked to cooked chicken.     

A simple quantum dot-based fluoroimmunoassay method for selective capturing and rapid detection of Salmonella Enteritidis on eggs

The aim of this paper was to demonstrate a rapid and selective fluorescence-linked immunoassay method based on quantum dots as the fluorescent marker for the detection of Salmonella Enteritidis on eggshell. Highly-fluorescent and water-soluble CdTe quantum dots were prepared by using thioglycolic acid and 1-thioglycerol as ligands and were then conjugated with anti-Salmonella antibodies. As a result of specific interaction, Salmonella Enteritidis were specifically captured by bioconjugated CdTe quantum dots which led to the detection of a fluorescent signal. The bacterial cell images were obtained using fluorescence microscopy. Under optimal conditions, the quenched fluorescence intensity increased linearly with the log total count of Salmonella Enteritidis ranging from 3 × 10² to 3 × 10⁷ CFU/mL within 1–2 h. The low detection limit was 1 × 10² CFU/mL without sample enrichment. This method was satisfactorily applied to the analysis of egg samples, which was demonstrated as a simple scheme for quick and selective detection of Salmonella Enteritidis on eggshell.     

Reduction of Escherichia coli O157, Listeria monocytogenes and Salmonella enterica sv. Typhimurium populations on fresh-cut bell pepper using gaseous ozone

Bacterial contamination is the main cause of food poisoning which can lead to diarrhoea, abdominal cramp, vomiting as well as death. Bacterial contamination can potentially be controlled by application of gaseous ozone due to its antibacterial activity. Therefore, the objective of this study was to investigate the efficacy of gaseous ozone for reducing food-borne pathogens such as Escherichia coli O157, Listeria monocytogenes and Salmonella enterica sv. Typhimurium on fresh-cut bell pepper. Efficacy of gaseous ozone to reduce bacterial populations was investigated in vitro and in vivo. Results showed that optimum effect of ozone on reducing bacterial populations was achieved with short term exposures of less than 6 h. Ozone reduced the bacterial population by disrupting bacterial cell structure, which lead to cellular death. Results also showed that bacterial cells have different resistance to ozone where ozone was more effective against L. monocytogenes, followed by E. coli O157 and Salmonella Typhimurium. Optimal reduction of the bacterial population on fresh-cut bell pepper was achieved with exposure to 9 ppm ozone for 6 h. This treatment reduced 2.89, 2.56 and 3.06 log of E. coli O157, Salmonella Typhimurium and L. monocytogenes populations, respectively. In conclusion, exposure to 9 ppm ozone for 6 h helps in reducing food-borne pathogen on fresh-cut bell pepper and has high potential to be an alternative sanitization treatment to reduce pathogen population on fruit.     

Decontamination of incoming beef trimmings with hot lactic acid solution to improve microbial safety of resulting dry fermented sausages – A pilot study

In the study, beef trimmings intended for sausage production were subjected to different decontamination treatments based on lactic acid-hot water combination, with aim to eliminate or reduce foodborne pathogens Escherichia coli O157, Salmonella Typhimurium and Listeria monocytogenes in resultant dry, fermented sausages. In finished sausages, produced from untreated trimmings, “natural” reductions of inoculated E. coli O157 and Salmonella Typhimurium were on average 1.9 logs, L. monocytogenes count remained unchanged, and no detectable concentrations of biogenic amines were found. The same type of sausages were also produced by using beef trimmings which was pathogen-inoculated and then decontaminated by: hot, 4% lactic acid in water solution (90 °C for 10 s; treatment HLA1); or hot, 4% lactic acid in water solution (85 °C for 20 s; treatment HLA2), or hot, 4% lactic acid in water solution (80 °C for 30 s; treatment HLA3). The use of HLA-decontaminated beef trimmings resulted in total E. coli O157 reductions of at least 3.9 logs and in total Salmonella Typhimurium reductions of at least 3.6 logs, whilst biogenic amines were not detected in finished sausages. The overall sensorial acceptability of finished sausages produced with HLA-decontaminated beef trimmings was somewhat diminished. Further work is required to optimise the HLA-based incoming beef treatments.     

Antibacterial properties of selenium nanoparticles and their toxicity to Caco-2 cells

The antibacterial properties of Se NPs were investigated against four foodborne pathogens (Escherichia coli O157:H7, Staphylococcus aureus, Salmonella, and Listeria monocytogenes). The cytotoxicity of Se NPs was also studied using the Caco-2 cell line. Se NPs at concentrations of 10 μg/mL or higher exhibited dose-dependent antimicrobial properties against S. aureus, but not on the other three pathogens. Se NPs also exhibited various degrees of toxicity on Caco-2 cells after 24 h of exposure. Cellular shrinkage and irregular shapes of treated bacterial cells indicated that the antimicrobial effects of Se NPs are bacteriostatic, not bactericidal. This is the first study to investigate the antimicrobial activity of Se NPs against important foodborne pathogens. The results of this study demonstrate that Se NPs can be used as an antimicrobial agent to inhibit the growth of S. aureus and can be potentially used for food safety applications.     

Single- and mixed-species biofilm formation by Escherichia coli O157:H7 and Salmonella,and their sensitivity to levulinic acid plus sodium dodecyl sulfate

The development of single- and mixed-species biofilms formed by Escherichia coli O157:H7 and Salmonella was observed, and the antimicrobial effectiveness of levulinic acid (LVA) plus sodium dodecyl sulfate (SDS) on the cells in single- and dual-species biofilms was determined. Biofilm-forming ability of single- and mixed-species cultures was observed by crystal violet staining and their resistance to levulinic acid plus SDS was determined by enumeration. Fluorescent protein-labeled E. coli O157:H7 and Salmonella were constructed and the bacterial composition of the biofilms after treatment with levulinic acid plus SDS was visualized by confocal laser scanning microscopy (CLSM). E. coli O157:H7 and Salmonella were antagonistic to each other, being more sensitive to levulinic acid plus SDS in mixed-species biofilms. Images captured by CLSM revealed that E. coli O157:H7 and Salmonella were distributed evenly in the single- and dual-species biofilms, and confirmed that the combination of levulinic acid and SDS was effective in inactivating bacterial cells in biofilms. Results revealed that levulinic acid with SDS may be used as a potential biofilm control intervention.     

Buffering effect of chicken skin and meat protects Salmonella enterica strains against hydrochloric acid but not organic acid treatment

This study investigated the buffering effect of chicken skin and meat by determining changes in the pH of phosphate buffered saline solutions (PBS; pH 2, 3, 5, 7, 9 and 11) before and after incubation at refrigeration temperature with these two chicken components. In addition, the effects of organic acids and hydrochloric acid on the survival of two strains each of Salmonella Typhimurium and Salmonella Enteritidis inoculated onto chicken skin and meat were determined. The Salmonella strains were enumerated before and after exposure to acid treatment and compared to Salmonella in PBS without chicken. Chicken meat buffered better than chicken skin and, for example, increased the pH 2 PBS to pH 4.8 (p < 0.001). Of the four acids acetic acid most rapidly reduced numbers of Salmonella on chicken, followed by citric acid, lactic acid and HCl. Acetic acid, lactic acid, citric acid and HCl effectively eliminated Salmonella at ∼ pH 3.8 (p < 0.001), ∼pH 2.5 (p < 0.05), ∼pH 2.9 (p < 0.05) and ∼pH 1.2 (p < 0.001), respectively. The buffering effect of chicken protected Salmonella against HCl at pH 2 but not from organic acids at the same pH. The ability of acetic acid to eliminate Salmonella on chicken meat at ∼ pH 4 suggests it has potential for application in commercial marination.     

Inactivation of foodborne pathogens in raw milk using high hydrostatic pressure

Plate counting, viability test, pulse field gel electrophoresis (PFGE) and transmission electron microscopy (TEM) were used to investigate the effect of high hydrostatic pressure (HHP) on Salmonella, Escherichia coli, Shigella and Staphyloccocus aureus in raw milk in order to determine the optimal inactivation conditions, and further understand the mechanisms of HHP on pathogens inactivation in food. The results exhibited that 300 Mpa treatment with 30 min duration at 25 °C was the optimal condition for Salmonella, E. coli, Shigella and S. aureus inactivation. Damage of the cell wall, cell membrane and cytoplasmic components by high pressure treatment can be observed in TEM micrographs. The injured cells could not be recovered, the growth rate of survivors was much lower than that of the untreated cells. PFGE showed neither corresponding DNA bands with same molecular weight nor DNA bands with same brightness could be found in the lanes between HHP treated pathogens and untreated ones. The results indicated that HHP processing can be applied to inactivate pathogens in food, the inactivation is mainly due to cell membrane damage, cell wall rupture and chromosome DNA degradation.     

Antimicrobial activity of ascorbic acid alone or in combination with lactic acid on Escherichia coli O157:H7 in laboratory medium and carrot juice

The antimicrobial effects of ascorbic acid alone and in combination with lactic acid, against Escherichia coli O157:H7 in Brain Heart Infusion (BHI) broth and in carrot juice as a food model was investigated. In control samples, E. coli O157:H7 continued to growth from 3.98 ± 0.2 log CFU and reached to 8.88 ± 0.1 log₁₀ CFU after 8 h at 37° C; however, bacterial population was undetectable level in BHI in the presence of 0.4% ascorbic acid and 0.2% lactic acid. In carrot juice, E. coli O157:H7 continue to grow from initial population count of 4.41 ± 0.9 log₁₀ CFU to 8.75 ± 0.07 log₁₀ CFU at 37 °C for 24 h. Similarly, the bacteria population was undetectable when 0.2 or 0.4% ascorbic acid and 0.2% lactic acid applied. Our findings suggest the application of ascorbic acid, in combination with lactic acid, may have potential as preservative to inhibit the growth of E. coli O157:H7 in food.     

Effect of Tween 20 on antibacterial effects of acidic,neutral and alkaline decontaminants on viability of Salmonella on chicken carcasses and survival in waste decontamination fluids

The effect of Tween 20 on antimicrobial effects of acidic (lactic acid), neutral (cetyl pyridinium chloride) and alkaline (trisodium phosphate) decontaminants to reduce the numbers of Salmonella inoculated to broiler carcasses were studied. In addition, survival of Salmonella in waste decontamination fluids was investigated. For this purpose, an average of 7 ± 1 log₁₀ cfu/ml Salmonella Enteritidis and Salmonella Typhimurium cocktail was surface-inoculated on to a total of 110 broiler carcasses. Contaminated carcasses were immersed in to tap water (control), lactic acid (LA) (1–2%), cetyl pyridinium chloride (CPC) (0.5–1%), or trisodium phosphate (TSP) (8%) and the combinations of these treatments with Tween 20 (TW20) (0.5%) for 15 min. Results indicated that, Salmonella numbers significantly decreased (P < 0.05) in all groups, except control and 1% LA. No significant difference was found between treatments with and without TW20. In waste decontamination fluids, 6.68 and 3.41 log₁₀ cfu/ml of Salmonella were recovered from control and CPC groups, respectively, while no viable Salmonella cell was detected in LA and TSP groups by direct plating. It was concluded that regardless of TW20, the antimicrobials tested were effective to reduce Salmonella in poultry carcasses. However, the pathogen may survive in neutral waste decontamination fluid such as CPC and can pose a risk for consumer health by contaminating the plant environment.     

Assessment of polyphenolic profile and antibacterial activity of pomegranate peel (Punica granatum) flour obtained from co-product of juice extraction

The aim of this work were to determine the polyphenolic profile and the antibacterial properties of pomegranate peel flour (PPF), in view to its application in the food industry as potential antimicrobial “natural” agent. For thus, the antibacterial properties of PPF were tested against: Listeria monocytogenes, Listeria innocua, Staphylococcus aureus, Pseudomonas aeruginosa, Escherichia coli and Salmonella sp. bacterial strains. The polyphenolic profile was determined by HPLC. The Total Phenolic and Total Flavonoid content were also determined. The HPLC analysis of the PPF, showed a total of eight phenolic compounds. Punicagalin was the main component found in PPF (16.67 mg/g) followed by ellagic acid (0.15 mg/g). PPF had antibacterial activity against all bacteria tested with minimal inhibitory concentrations comprised between 20 and 50 mg/mL. The antimicrobial activity was in a decreasing order: Salmonella sp = E. coli = S. aureus = L. monocytogenes > P. aeruginosa > L. innocua. The antibacterial properties of pomegranate peel flour suggested that it is a promising antibacterial agent.     

Modeling the growth rates of Escherichia coli spp. and Salmonella Typhimurium LT2 in baby spinach leaves under slow cooling

After field harvest, baby spinaches are transported to the packing shed where they are cooled by forced air systems. If contaminated, the temperature of spinaches will affect the number of pathogens in the leaves, and effective temperature control is critical to restrict their growth. Hence, the need to assess the impact of cooling practices on the growth of pathogens in leafy greens. The Baranyi model was used to describe the experimental data and build a dynamic model to predict microorganism growth rate in baby spinach leaves as function of temperature.Baby spinach leaves, inoculated with 10⁴ CFU/ml of Salmonella Typhimurium LT2 or 10² CFU/ml of an Escherichia coli cocktail, and were maintained at temperatures ranging from 10 to 37 °C for 30 h. At 10–30 °C, the E. coli strains grew significantly more (～2–4 log cycles) than the Salmonella strain (～0.11–2.4 log cycles) while at 37 °C, both bacterial populations increased by ～6 log cycles for 30 h. The growth kinetics of each microorganism followed the Baranyi model. The maximum bacterial population increased with temperature and the values were similar for both bacteria. The theoretical minimum temperature for growth was 5.88 °C and 4.76 °C for Salmonella and E. coli, respectively. The dynamic model was validated with an experimental linear cooling profile (slow cooling) and could be incorporated into a risk assessment tool to evaluate the growth of pathogens in baby spinach during processing and distribution.     

Inactivation by 405 ± 5 nm light emitting diode on Escherichia coli O157:H7, Salmonella Typhimurium,and Shigella sonnei under refrigerated condition might be due to the loss of membrane integrity

The objective of this study was to evaluate the antibacterial effect of 405 ± 5 nm light emitting diode (LED) on Escherichia coli O157:H7, Salmonella Typhimurium and Shigella sonnei. Its antibacterial mechanism was also investigated by determining the permeability of bacterial membrane and DNA degradation. Bacterial strains in phosphate-buffered saline were exposed to 405 ± 5 nm LED to a final dose of 486 J/cm² (7.5 h) at 4 °C. The inactivation curves were fitted by Weibull model to compare the sensitivities of pathogens to the LED illumination by calculating the decimal reduction times (t_R). The bacterial sensitivity to bile salts and NaCl by LED illumination was also determined. LIVE/DEAD^® BacLight™ staining as well as comet assay and DNA ladder analysis were carried out to determine the bacterial membrane integrity and DNA degradation, respectively. Results showed that LED illumination inactivated 1.0, 2.0, and 0.8 log CFU/ml for E. coli O157:H7, S. Typhimurium, and S. sonnei for 7.5 h, respectively. The comparison of t_R values demonstrated that S. Typhimurium was found to be the most (P < 0.05) susceptible strain to LED illumination. Regardless of the bacterial strain, the sensitivity of illuminated bacterial cells to bile salts and NaCl considerably increased compared to non-illuminated controls. Furthermore, LIVE/DEAD^® assay clearly showed that LED illumination resulted in loss of bacterial membrane permeability. On the other hand, no DNA degradation was observed by both comet assay and DNA ladder analysis. Therefore, these results suggest that the antibacterial effect of 405 ± 5 nm LED might be partly attributed to the physical damage to bacterial cell membrane. This study proposes that 405 ± 5 nm LED under refrigerated conditions may be effective to control the pathogens on foods.     

Efficacy of lactic acid in reducing foodborne pathogens in minimally processed lotus sprouts

Fresh lotus sprout is easily browned and perishable due to microbial growth and degradation. Therefore, browning and foodborne pathogen have become the most serious problems. The objective of this study was to investigate the effect of lactic acid (0.25%, 0.5%, 1% and 2% (v/v)) on reduction of foodborne pathogens, such as Escherichia coli O157:H7, Salmonella Typhimurium, and Listeria monocytogenes, in lotus sprouts. Tap water and sodium hypochlorite (200 mg/l) were used as control treatments. Results indicated that tap water caused a slight reduction (<0.5 log) in the microbial loads. The sodium hypochlorite treatment led to 1.3 log reductions of the microbial population. When treated with 0.5% and 2.0% lactic acid solutions, 1.5 and 2.3 log reductions were achieved, respectively. The effectiveness of lactic acid treatment increased with the increase of lactic acid concentration. Results showed that the lactic acid treatment at 0.5% or higher was effective to reduce foodborne pathogens in lotus sprouts. The L* values of samples treated with lactic acid decreased slightly during storage. Furthermore, the lactic acid treatment contributed to slow accumulation of red color on lotus sprouts, which was more effective than sodium hypochlorite treatment to reduce the discoloration of lotus sprouts. These results indicated that lactic acid can be used to improve the color and safety of minimally processed lotus sprouts.     

Combined sustainable sanitising treatments to reduce Escherichia coli and Salmonella Enteritidis growth on fresh-cut kailan-hybrid broccoli

The effects of peroxyacetic acid (PA), neutral electrolysed water (NEW), ultraviolet C light (UV-C) and superatmospheric O₂ packaging (HO), single or combined, on the growth rate of Escherichia coli and S. Enteritidis inoculated onto fresh-cut kailan-hybrid broccoli were studied throughout 14 days of shelf life at 5 and 10 °C. As controls, unwashed, water-washed and NaClO-washed were used. PA and NEW showed a better sanitising effect than NaClO against both E. coli/S. Enteritidis with reductions of 2.2/2.7 and 2.6/2.6 log CFU g⁻¹, respectively. UV-C attained E. coli/S. Enteritidis decreases of 1.3–1.4/2.1–2.2 log CFU g⁻¹ compared to unwashed samples. The bacteriostatic effects of PA or NEW were improved when they were combined with UV-C, decreasing E. coli and S. Enteritidis counts by about 3 log CFU g⁻¹. After 14 days, PA and NEW-treated samples attained E. coli/S. Enteritidis reductions at 5 °C of 2.3/1.4 and about 1 log CFU g⁻¹, respectively. Storage of those samples at 10 °C masked that sanitising effect. At both storage temperatures, UV-C-treated samples registered lower E. coli and S. Enteritidis reductions (or higher increases for S. Enteritidis at 10 °C) regarding conventional NaClO-sanitized samples or other single treatments. However, PA, NEW or UV-C-treated samples under HO at both storage temperatures showed better bacterial control than individual treatments with the greatest effectiveness for UV-C + HO. Triple combination did not imply an enhanced benefit over double combinations. Conclusively, PA, NEW and UV-C seems to be effective emergent alternatives to NaClO to reduce initial E. coli and S. Enteritidis populations in fresh-cut kailan-hybrid broccoli. Storage at 5 or 10 °C under HO greatly controlled microbial growth.     

Sublethal injury and recovery of Escherichia coli O157:H7 and K-12 after exposure to lactic acid

Lactic acid can induce sublethal injury of Escherichia coli. When conditions become favorable, injured E. coli can recover physiological function and fully virulence, which is a great concern in the field of food safety. The injury and recovery of E. coli O157:H7 and K-12 by lactic acid were investigated in this study. Sublethally injured E. coli cells widely persisted after a 60-min exposure to lactic acid with different pH values (E. coli O157:H7: pH 3.0–4.6, E. coli K-12: pH 3.4–5.0). The sublethally injured ratio of E. coli O157:H7 and K-12 by lactic acid decreased as incubation temperature decreasing. Both sublethally injured E. coli O157:H7 and K-12 induced by lactic acid could be completely recovered in trypticase soy broth at 37 °C within 60 min. For both E. coli O157:H7 and K-12, sodium pyruvate, Tween 80, or certain cations (Mn, Fe, or Zn) could significantly increase the recovery ratio. The recovery ratios of injured E. coli K-12 and O157:H7 were only 74.2% and 92.6% after 80 min incubation in minA, respectively. But they can both be completely recovered within 80 min in minA with sodium pyruvate, with Tween 80, or with cations (Mn, Fe, or Zn). But Mg and Ca cations did not affect the recovery time. The understanding of injury and recovery of E. coli could contribute to develop effective decontaminating treatment by lactic acid, and develop techniques for detecting sublethally injured E. coli cells.     

Simulation of decontamination and transmission of Escherichia coli O157:H7, Salmonella Enteritidis,and Listeria monocytogenes during handling of raw vegetables in domestic kitchens

Epidemiological data indicates that a large number of foodborne illnesses are attributed to cross-contamination during food preparation in the domestic kitchen. The objectives of this study were to evaluate the efficiency of household washing practices in removing Escherichia coli O157:H7, Listeria monocytogenes, and Salmonella Enteritidis on artificially contaminated lettuce and to determine the transfer rate of these three foodborne pathogens from contaminated lettuce to wash water, tomato, cabbage, and cutting boards during washing and cutting processes. Washing under the running tap water with scrubbing for 60 s was the most effective method in reducing pathogen populations by 1.86–2.60 log₁₀ CFU/g. Also, final rinsing and scrubbing practices were found to enhance the efficiency of washing treatment. In this study, the transfer rates of S. Enteritidis, E. coli O157:H7, and L. monocytogenes from cutting board to cabbage and tomato via cutting process (17.5–31.7%) were higher (P < 0.05) than from wash water to cabbage and tomato (0.8–23.0%) during washing treatment. Overall, our findings suggest that wash water and cutting board can be potential vehicles in the dissemination of foodborne pathogens. Therefore, there is a need to promote consumer awareness for proper handling practices in the kitchen to minimise the risk of foodborne infection.