Mode of action of sakacin C2 against Escherichia coli

Sakacin C2 was a novel broad-spectrum bacteriocin produced by Lactobacillus sakei C2 isolated from traditional Chinese fermented cabbage. Sakacin C2 could inhibit not only Gram-positive bacteria but also Gram-negative bacteria. In this paper, the mode of action of sakacin C2 against Escherichia coli ATCC 25922, a typical Gram-negative bacterium, was determined. Addition of 360 AU ml^?1 of sakacin C2 led to nearly entire inhibition of cell growth for at least 12 h, depolarization of trans-membrane electrical potential, efflux of UV-absorbing materials, fragmentary of cell membrane and permeabilization of cell to propidium iodide. These results suggested that the mode of sakacin C2 against E. coli ATCC 25922 was depolarization of trans-membrane electrical potential, pore formation in cell membrane and complete disintegration ultimately.     

Antimicrobial effect of cranberry juice and extracts

The antimicrobial effect of cranberry juice and of three cranberry extracts (water-soluble (E1) and apolar phenolic compounds (E2), and anthocyanins (E3)) was investigated against seven bacterial strains (Enterococcus faecium resistant to vancomycin (ERV), Escherichia coli O157:H7 EDL 933, Escherichia coli ATCC 25922, Listeria monocytogenes HPB 2812, Pseudomonas aeruginosa ATCC 15442, Salmonella Typhimurium SL1344, and Staphylococcus aureus ATCC 29213). Each cranberry sample was analyzed to determine the minimum inhibitory concentration (MIC) and the maximal tolerated concentration (MTC) at neutral pH. The results, reported in μg phenol/mL, indicated that all the bacterial strains, both Gram-positive and Gram-negative, were selectively inhibited by the cranberry phenolic compounds. The extract rich in water-soluble phenolic compounds caused the most important growth inhibitions. The bacteria ERV, and to a lesser degree, P. aeruginosa, S. aureus and E. coli ATCC 25922, were the most sensitive to the antimicrobial activity of extract E1. The growth of P. aeruginosa and E. coli ATCC was also affected by the presence of the anthocyanin-rich cranberry extract E3, although the observed antibacterial effect was not as important as with extract E1. In general, L. monocytogenes, E. coli O157:H7 and S. Typhimurium were the most resistant to the antibacterial activity of the cranberry extracts. Within 30 min of exposure with pure neutralized cranberry juice, L. monocytogenes and ERV were completely inactivated.     

A novel bacteriocin with a broad inhibitory spectrum produced by Lactobacillus sake C2, isolated from traditional Chinese fermented cabbage

By excluding the effects of organic acids and hydrogen peroxide, strain C2 producing a bacteriocin strongly inhibited Staphylococcus aureus ATCC 63589 and Escherichia coli ATCC 25922 was selected from 300 lactic acid bacteria isolated from traditional Chinese fermented cabbage. Strain C2 was identified as Lactobacillus sakei by phenotypical and physiological tests and 16S rDNA identification. This bacteriocin, which was designated sakacin C2, was purified by cold ethanol and Sephadex G50 column chromatography for further studies. The molecular weight of sakacin C2 was 5.5 kDa by Tris-Tricine SDS–PAGE, which was the largest among all known sakacins. Sakacin C2 exhibited a wide range of antimicrobial activity, strong heat stability (15 min at 121 °C) and pH stability (pH 3.0–8.0). Sakacin C2 was sensitive to protease but insensitive to lipase, α-amylase and β-amylase. These characters suggested that sakacin C2 was a novel Class II bacteriocin with a broad inhibitory spectrum and might broaden the application range of bacteriocins from LAB in the food industry.     

Efficacy of low concentration neutralised electrolysed water and ultrasound combination for inactivating Escherichia coli ATCC 25922, Pichia pastoris GS115 and Aureobasidium pullulans 2012 on stainless steel coupons

The sanitising effect of low concentration neutralised electrolysed water (LCNEW, pH: 7.0, free available chlorine (FAC): 4 mg/L) combined with ultrasound (37 kHz, 80 W) on food contact surface was evaluated. Stainless steel coupon was chosen as attachment surface for Escherichia coli ATCC 25922, Pichia pastoris GS115 and Aureobasidium pullulans 2012, representing bacteria, yeast and mold, respectively. The results showed that although LCNEW itself could effectively reduce survival population of E. coli ATCC 25922, P. pastoris GS115 and low concentration A. pullulans 2012 in planktonic status, LCNEW combined with ultrasound showed more sanitising efficacy for air-dried cells on coupons, with swift drops: 2.2 and 3.1 log CFU/coupon reductions within 0.2 min for E. coli ATCC 25922 and P. pastoris GS115, respectively and 1.0 log CFU/coupon reductions within 0.1 min for A. pullulans 2012. Air-dried cells after treatment were studied by atomic force microscopy (AFM)/optical microscopy (OM) and protein leakage analyses further. All three strains showed visible cell damage after LCNEW and LCNEW combined with ultrasound treatment and 1.41 and 1.73 μg/mL of protein leakage were observed for E. coli ATCC 25922 and P. pastoris GS115, respectively after 3 min combination treatment, while 6.22 μg/mL of protein leakage for A. pullulans 2012 after 2 min combination treatment. For biofilms, LCNEW combined with ultrasound also significantly reduced the survival cells both on coupons and in suspension for all three strains. The results suggest that LCNEW combined with ultrasound is a promising approach to sanitise food equipment.     

Inhibition of foodborne pathogens by Hf-1, a novel antibacterial peptide from the larvae of the housefly (Musca domestica) in medium and orange juice

Antibacterial molecules from edible insects may serve as a potentially significant group of food preservatives. Hf-1, a novel peptide from larvae of housefly (Musca domestica) with molecular weight approximately 8.0 KD, inhibited food pathogens Escherichia coli ATCC 25922, Pseudomonas aeruginosa ATCC 27553, Salmonella typhimurium 50013, Shigella dysenteriae 51302, Staphylococcus aureus 6538 and Bacillus subtilis 9372 with MIC ranging from 18 to 72 μg/ml. The presence of EDTA can enhance Hf-1 activity against Gram-negative bacteria. Hf-1 was bactericidal in orange juice, showing an antibacterial activity approximately equivalent to sodium benzoate. The mode of action of Hf-1 involved decreasing the cell surface hydrophobicity and damaging the cell membrane. The results suggested Hf-1 has the potential to be used as the food preservative.     

Antimicrobial effects of fractions from cranberry products on the growth of seven pathogenic bacteria

The antimicrobial effect of thirty HPLC fractions of different polarity obtained from two cranberry juices and three extracts (anthocyanins, water-soluble and apolar phenolic compounds) isolated from frozen cranberries and pomace was investigated against seven bacterial strains (Enterococcus faecium resistant to vancomycin (ERV), Escherichia coli O157:H7 EDL 933, Escherichia coli ATCC 25922, Listeria monocytogenes HPB 2812, Pseudomonas aeruginosa ATCC 15442; Salmonella Typhimurium SL1344 and Staphylococcus aureus ATCC 29213) The minimum inhibitory concentration (MIC) and the maximal tolerated concentration (MTC) of each fraction were determined for each pathogen using a 96-well microtiter plate method. The results, reported in μg phenol/mL, indicated that all the bacterial strains, both Gram-positive and Gram-negative, were selectively inhibited by the cranberry phenolic compounds. All pathogens were very sensitive to at least seven fractions with MTCs below 2 μg phenol/mL and five fractions with MICs below 10 μg phenol/mL. In addition, four fractions rich in apolar phenolic compounds were very efficient against all bacteria with MICs below 10 μg phenol/mL, and twenty five fractions completely inhibited microbial growth with MICs below100 μg phenol/well. L. monocytogenes exhibited the highest sensitivity with twelve very active fractions (MTCs and MICs below 1 and 10 μg phenol/mL, respectively) while E. coli O157H7 was the least sensitive to twenty seven fractions (with the highest MICs). Also, it appears that the technological process to manufacture cranberry juice can reduce the antimicrobial activity of phenolic fractions.     

Characterization of a novel bacteriocin produced by Lactobacillus sakei LSJ618 isolated from traditional Chinese fermented radish

A novel bacteriocin, sakacin LSJ618, produced by the strain Lactobacillus sakei LSJ618 isolated from traditional Chinese fermented radish, was studied. L. sakei LSJ618 was identified by both phenotypical and physiological tests combined with 16S rDNA sequence analysis. Sakacin LSJ618 is sensitive to hydrolytic enzymes including lipase, is stable between pH 2-8, and is heat resistant (30 min at 121 °C). Sakacin LSJ618 exhibits inhibitory activity against food-spoiling bacteria and food-borne pathogens, including the Gram-positive Listeria monocytogenes, Staphylococcus aureus, Sarcina sp., Micrococcus luteus, and the Gram-negative Proteus sp. and Escherichia coli, but not against most of the lactic acid bacteria tested. Maximal production of bacteriocin was reached in the late stationary phase, and inhibitory activity declined within 26 h. The mode of action of sakacin LSJ618 was determined to be bactericidal, as evidenced by its action upon Micrococcus tetragenus. After partial purification by ammonium sulfate precipitation and Sephadex G-25 chromatography, the molecular weight of sakacin LSJ618 was determined to be 5.2 kDa by Tricine-SDS-PAGE. The identified properties of sakacin LSJ618 indicate that it is a novel bacteriocin with potential application as a biopreservative in the food industry.     

Pulsed electric field inactivation of E. coli O157:H7 and non-pathogenic surrogate E. coli in strawberry juice as influenced by sodium benzoate,potassium sorbate,and citric acid

Current FDA regulations require that juice processors achieve a 5 log CFU/ml reduction of a target pathogen prior to distributing products. Whereas thermal pasteurization reduces the sensory characteristics of juice, pulsed electric field (PEF) treatments can be conducted at lower temperatures and may preserve sensory characteristics.Escherichia coli O157:H7 (ATCC 43895) and a non-pathogenic E. coli (ATCC 35218), respectively, were inoculated into single-strength strawberry juice with or without 750 ppm sodium benzoate (SB), 350 ppm potassium sorbate (PS), and 2.7% citric acid (CA). Juice was treated at outlet temperatures of 45, 50 and 55 °C at a field strength of 18.6 kV/cm for 150 μs with a laboratory-scale PEF unit. Inactivation of surrogate E. coli at 45, 50, and 55 °C were 2.86, 3.12, and 3.79 log CFU/ml, respectively, in plain juice (pH 3.4), and 2.75, 3.52, and 5.11 with the addition of benzoic and sorbic acids (pH 3.5). Inactivation of E. coli O157:H7 under the same conditions were 3.09, 4.08, and 4.71 log CFU/ml, respectively, and 2.27, 3.29, and 5.40 with antimicrobials. E. coli O157:H7 in juice with antimicrobials and 2.7% CA (pH 2.7) treated with PEF was reduced by 2.60, 4.32 and 6.95 log CFU/ml at 45, 50 and 55 °C while the surrogate E. coli decreased by 3.54, 5.69, and 7.13 log under the same conditions. When juice (pH 2.7) was held for 6 h without PEF treatment, higher numbers of E. coli 35218 (7.17 log CFU/ml) were inactivated than of acid-resistant E. coli O157:H7 (3.89 log). Slightly greater PEF inactivation of E. coli O157:H7 than of the surrogate bacterium indicates that E. coli ATCC 35218 provides a margin of safety when used as a surrogate for O157:H7 in plain strawberry juice or in juice + SB + PS at 45–50 °C, or with SB + PS and CA at 55 °C.     

Bactericidal effects of Cinnamon cassia oil against bovine mastitis bacterial pathogens

Organic food production is expanding rapidly. However, this industry is hampered by the lack of effective antimicrobial agents which can be used in organic food production. This study examined the antimicrobial activity of Cinnamon cassia oil against major pathogens causing bacterial bovine mastitis, its miscibility in milk and possible antimicrobial mechanisms. C. cassia oil had inhibitory activity against all tested pathogen isolates from bovine mastitis. We conducted disk diffusion assay and found that discs with 20 μL of 2% (v/v) C. cassia oil solution resulted in inhibition zones of 29.6, 19.1, 27.0, 33.3 and 30.7 mm for Staphylococcus aureus, Staphylococcus epidermidis, Staphylococcus hyicus, Staphylococcus xylosus and Escherichia coli 29, respectively. The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of C. cassia oil was 0.00625% and 0.025% (v/v) for S. hyicus, 0.025% and 0.10% (v/v) for E. coli 29, and 0.0125% and 0.05% for S. aureus, S. epidermidis and S. xylosus, respectively. We selected two common mastitis pathogens, a representative S. aureus isolate and E. coli 29 for further analyses. Based on time-kill assay in LB broth with 0.15% agar, 2MBC of C. cassia oil generated bactericidal effects on S. aureus and E. coli 29 within 30 min, and 4MBC caused 6 log reduction of S. aureus and E. coli 29 within 30 min. In milk, C. cassia oil at 4MBC reduced ∼6.0 Log₁₀ CFU/ml of S. aureus and E. coli 29 to undetectable level within 8 h. Using propidium iodide staining, we observed membrane damage on both S. aureus and E. coli 29 cells during incubation with C. cassia oil. In addition, C. cassia oil treatment at MIC impaired membrane integrity of E. coli and S. aureus, which was followed by a decrease in ATP synthesis. Bacterial extracellular signaling quorum sensing orchestrates important events related to bacterial pathogeneses through excreting autoinducer (AI). Sub-inhibitory concentration of C. cassia oil repressed AI-2, a universal signal molecule mediating quorum sensing, production in S. aureus and E. coli 29 isolates. Collectively, our data show that C. cassia oil provides an exciting potential to be used as an alternative antimicrobial for bovine mastitis in organic dairy farms.     

Antimicrobial activity and physical properties of protein films added with cell-free supernatant of Lactobacillus rhamnosus

Antimicrobial and physical properties of whey protein isolate (WPI) or calcium caseinate (CC) films added with cell-free supernatant of Lactobacillus rhamnosus NRRL B-442 were evaluated. Antimicrobial activity was probed against Listeria monocytogenes Scott A, Staphylococcus aureus ATCC 29413, Escherichia coli ATCC 25922, or Salmonella enterica serovar Typhimurium ATCC 14028. Cell-free supernatant was obtained by centrifugation and filtration from cultures of L. rhamnosus in MRS broth, freeze-dried, and rehydrated to add 6, 12, or 18 mg/ml to protein film solution. Films' inhibition zones were determined by agar disk diffusion assay against tested microorganisms. Films' thickness, puncture strength, color, moisture content, solubility, and water vapor permeability (WVP) were evaluated. Noticeable antimicrobial activity (about 3 mm) was observed against E. coli, L. monocytogenes, S. aureus, or S. Typhimurium when 18 mg/ml of cell-free supernatant were added. Gradual and significant (p < 0.05) increments were obtained in thickness, color, and solubility when different increasing concentrations of supernatant were added. Reductions in WVP and puncture strength were observed when adding supernatant. Antimicrobial films were brown colored and with variable moisture contents. WPI films were significantly (p < 0.05) better than CC films for most evaluated properties. Protein films added with cell-free supernatant are an interesting alternative to develop natural antimicrobial films that can have a potential food application as wrappings or coatings.     

Effects of Lactobacillus sakei C2 and sakacin C2 individually or in combination on the growth of Listeria monocytogenes,chemical and odor changes of vacuum-packed sliced cooked ham

The individual usage of Lactobacillus sakei C2 and sakacin C2 had an inhibitory effect against Listeria monocytogenes CMCC 54002, and the combination of L. sakei C2 and sakacin C2 exhibited a bactericidal action. L. sakei C2 and sakacin C2, individually or in combination, significantly lowered the pH values, proteolysis degree and odor score, and the effects were better when they were used in combination (P < 0.05). Moreover, L. sakei C2 exhibited certain anti-oxidative activity. These results showed that the usage of L. sakei C2 and its bacteriocin effectively controlled the growth of L. monocytogenes CMCC 54002, excessive proteolysis and the production of spoilage odor, did not have any unfavorable effects on the quality of vacuum-packaged sliced ham. Therefore, L. sakei C2 and its bacteriocin would provide an effective hurdle to improve the safe and quality, and would contribute to prevent the lipid oxidation of vacuum-packed sliced cooked ham at refrigeration temperature.     

In vitro enhancement of antibiotic susceptibility of drug resistant Escherichia coli by cinnamaldehyde

Cinnamaldehyde is a natural antimicrobial compound that has been found to damage the cytoplasmic membrane, inhibit septum development and cause cell elongation, as well as induce oxidative stress in Escherichia coli. Thus, cinnamaldehyde may be of value as a natural compound to enhance susceptibility of drug resistant E. coli to antibiotics in livestock production. This study examined the ability of cinnamaldehyde to increase the susceptibility of E. coli to antibiotics using the checkerboard method. Interactions between the antimicrobials were characterized using fractional inhibitory concentration (FIC) values. All tested E. coli strains were resistant to erythromycin and bacitracin but were susceptible to penicillin G and ampicillin. Strains 8WT, ATCC 23739 and 02:0627 were resistant to novobiocin and the latter two strains were also resistant to tetracycline. Cinnamaldehyde synergistically increased the susceptibility of all E. coli strains to erythromycin (FIC ≤ 0.5). Another synergistic effect between tetracycline and cinnamaldehyde was observed when tested against E. coli ATCC 23739 (FIC = 0.3). Cinnamaldehyde synergistically and additively reduced the MIC of novobiocin when tested against ATCC 23739 and 02:0627 (FIC ≤ 0.5) or 8WT (FIC = 1), respectively, suggesting that E. coli strains may respond differently to challenge by the cinnamaldehyde-novobiocin combination. With all strains, cinnamaldehyde was not effective at reducing the MIC value of bacitracin. Findings of this study suggest that cinnamaldehyde may be used in combination with several antibiotics to enhance susceptibility of drug resistant E. coli.     

Effects of spray volume, type of surface tissue and inoculum level on the survival of Escherichia coli on beef sprayed with 5% lactic acid

Membrane, fat and cut muscle surfaces of beef were inoculated with Escherichia coli at numbers about 4, 1 or −1 log cfu/cm². The inoculated meat was sprayed with water or 5% lactic acid at volumes of 0.5, 0.1 or 0.02 ml/cm². Spraying with water reduced the numbers of E. coli on membrane surfaces by up to 1 log unit, but had little effect on the numbers of E. coli on fat or cut muscle surfaces. Spraying with 5% lactic acid reduced the highest numbers of E. coli on membrane surfaces by up to 4 log units; but those numbers on fat or cut muscle surfaces were reduced by ≤1.5 log unit, and the reductions declined with decreasing volumes of 5% lactic acid. With inocula of 1 log cfu/cm², spraying lactic acid in any volume reduced the numbers of E. coli on membrane or fat surfaces by about 1 log unit, and the numbers on cut muscle surfaces by between 0.8 and 0.2 log unit. E. coli were detected in enrichment cultures of samples from all surfaces inoculated with E. coli at −1 log cfu/cm² and sprayed with 5% lactic acid at 0.5 ml/cm². The findings indicate that spraying relatively heavily contaminated cuts or trimmings with 5% lactic acid at ≥0.1 ml/cm² can be expected to reduce numbers of E. coli and, presumably, associated pathogens by between 0.5 and 1 log unit. However, such a treatment is likely to be at best marginally effective for reduce the numbers of these organisms on lightly contaminated product.     

Efficacy of pulsed electric fields for the inactivation of indicator microorganisms and foodborne pathogens in liquids and raw chicken

This study investigated the ability of pulsed electric fields (PEF) to inactivate a range of microorganisms in liquid media and on raw chicken meat. The susceptibilities of ten Campylobacter isolates (seven Campylobacter jejuni isolates and three Campylobacter coli isolates), Escherichia coli (ATCC 25922) and Salmonella Enteritidis (ATCC 13076) to PEF in liquid media were investigated. All Campylobacter isolates tested in liquid were susceptible to PEF treatment (65 kV/cm, 5 μs, 500 Hz) with reductions of between 4.33 and 7.22 log₁₀ CFU/mL observed for the longest treatment (30 s). Significant differences in susceptibility were observed between Campylobacter isolates subjected to equivalent PEF treatments ranging from 2.41 to 5.19 log₁₀ CFU/mL. Campylobacter isolates processed in liquid media were found to be more sensitive to PEF than E. coli and S. Enteritidis (P < 0.05). The application of PEF (3.75 and 15 kV/cm, 10 μs, 5 Hz) to inoculated samples of raw chicken did not result in any significant reductions in total viable counts, Enterobacteriaceae, C. jejuni, E. coli or S. Enteritidis. Therefore, under the conditions used in this study, PEF technology may not be suitable as a food safety intervention measure for the control of microbial contaminants on broilers during processing although it may have potential to reduce contamination of process water (e.g. scald or spin chill water).     

Antimicrobial efficacy of grape seed extract against Escherichia coli O157:H7 growth,motility and Shiga toxin production

Escherichia coli O157:H7 produces Shiga toxin (Stx) which is heat stable and causes Hemolytic Uremic Syndrome (HUS), a serious disease associated with bloody diarrhea and even death. To ensure food safety, both live E. coli O157:H7 and its toxin production in food products need to be controlled. Natural ingredients with inhibitory effects on E. coli O157:H7 growth and toxin production are top choices of antimicrobials for the food industry. The objectives of this study were to evaluate efficacy of grape seed extract (GSE) against the growth, swimming motility and Stx production of E. coli O157:H7. The disc diffusion assay indicated that 3.2 mg GSE per disc resulted in an inhibition zone of 14.8 ± 0.21 mm. The minimal inhibitory concentration of GSE against E. coli O157: H7 was 4.0 mg/ml. At high inoculation level (1 × 10⁷ CFU/ml), including GSE at 0.25–2.0 mg/ml reduced Stx production without inhibiting E. coli O157:H7 growth. At 5 × 10⁵ CFU/ml inoculation level, 2.0 and 4.0 mg/ml GSE effectively inhibited the growth of E. coli O157:H7 for at least 72 h, however, a low level of GSE (0.125–1.0 mg/ml) enhanced E. coli O157:H7 growth and Stx2 production. At 4 mg/ml, GSE completely abolished Stx2 production in addition to it bactericidal effect against E. coli O157:H7. In addition, GSE at concentration as low as 0.125% blocked the swimming motility, which is important for E. coli O157:H7 surface adherence. In conclusion, GSE is effective in inhibiting the motility of E. coli O157:H7, GSE shows potential to be used as a natural antimicrobial to control E. coli O157:H7.     

Purification and partial characterization of a novel bacteriocin produced by Lactobacillus casei TN-2 isolated from fermented camel milk (Shubat) of Xinjiang Uygur Autonomous region,China

Identification, characterization and assessment of novel bacteriocins for their potential use as biopreservatives continue to be highlighted in LAB research from past to present. A bacteriocin-producing Lactobacillus casei TN-2 strain was isolated from fermented camel milk (Shubat) of Xinjiang Uygur Autonomous region, China, after which the bacteriocin (designated as caseicin TN-2) was purified by performing ammonium sulfate precipitation, gel filtration, anion exchange chromatography and reversed-phase HPLC separation. According to MS spectrum, the molecular mass of caseicin TN-2 was 6352 Da, which was significantly different from previous reported bacteriocins produced by L. casei strains. Antibacterial activity of caseicin TN-2 was retained over a wide pH range and survived a heat treatment of 121 °C for 20 min. It was sensitive to proteases, such as trypsin and papain. Caseicin TN-2 exhibited a broad antimicrobial spectrum against Gram-positive and Gram-negative food-borne pathogenic strains including some antibiotic-resistant strains. It was found that the minimum inhibitory concentration of caseicin TN-2 to Escherichia coli ATCC25922 and Staphylococcus aureus ATCC25923 was 2.5 mg/mL and 5 mg/mL respectively. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) analyses were carried out to investigate the effect of caseicin TN-2 on the target cells, where it was demonstrated that the bacteriocidal mode of action was pore formation in the cytoplasmic membrane.     

Antibacterial activity of bovine milk lactoferrin on the emerging foodborne pathogen Cronobacter sakazakii: Effect of media and heat treatment

Cronobacter sakazakii is a pathogen transmitted by food, with high osmotic resistance and tolerance to desiccation, which affects mainly to newborns, infants and immunocompromised adults. C. sakazakii infection in infants has been associated with consumption of powdered milk. The purpose of this study was to evaluate the antibacterial activity of native and iron-saturated bovine lactoferrin (bLF) (from 0.5 to 5 mg/ml) on non-desiccated and desiccated C. sakazakii (10⁴ CFU/ml) in different media (phosphate buffer, bovine skim milk and whey). In general, native bLF was the only effective form that inhibited growth of C. sakazakii in all media, its activity increasing with concentration and time of incubation. These results suggest that the antibacterial effect of bLF on C. sakazakii is mainly due to iron sequestration. However, iron-saturated bLF showed some effect by reducing the viability of C. sakazakii in whey. There has not been observed an increased sensitivity of desiccated bacteria to native bLF in phosphate buffer. However, although the antibacterial activity of native bLF against non-desiccated C. sakazakii was drastically reduced in milk or whey compared to phosphate buffer, there was a certain activity when it was assayed against desiccated cells in those media. The effect of some heat treatments on the antibacterial activity of native bLF was evaluated and only those of 72 °C for 15 s, 85 °C for 15 s, and 63 °C for 30 min maintained its whole activity.     

Carvacrol nanoemulsion combined with acid electrolysed water to inactivate bacteria,yeast in vitro and native microflora on shredded cabbages

Carvacrol is an effective antimicrobial agent originated from essential oils, this natural antimicrobial agent has higher consumer acceptance compared to chemical agents. Due to the low solubility of carvacrol in water, carvacrol was delivered as a nanoemulsion. A carvacrol nanoemulsion contained 3.5% (w/w) oil phase (1% carvacrol and 2.5% corn oil, w/w) and 3.5% (w/w) Tween 80 was produced by ultrasonification at 10 min using 100% amplitude; the median particle size was 309 ± 19 nm. The nanoemulsion was shelf-life stable for 1 month without any significant changes in particle size. When applied against Escherichia coli ATCC 25922 and Pichia pastoris GS115 growth in nutrient broth, carvacrol nanoemulsion (0.5% w/w carvacrol) achieved 3 log reductions of microorganisms. When microorganisms were fixed and dried on stainless steel coupon surface, the carvacrol nanoemulsion treatment was more effective on E. coli than P. pastoris with about 5 and 0.3 log reduction of viable count, respectively. The native microflora on shredded cabbages was challenged by combining carvacrol nanoemulsion and acidic electrolysed water (AEW) that contained ≤ 4 mg/L free available chlorine (FAC). The treatment reduced about 0.5 log of aerobic mesophilic and psychrotropic bacteria counts and the antimicrobial activity of carvacrol nanoemulsion and AEW lasted up to 2 days. The results indicated that carvacrol nanoemulsion is promising in controlling the safety of fresh-cut vegetables.     

Comparison of a continuous flow dipper well and a reduced water dipper well combined with ultraviolet radiation for control of microbial contamination

Continuous flow (CF) dipper wells, or small countertop sinks, are used in the foodservice industry for rinsing utensils such as stirring spoons and dishers. In addition, these dipper wells are designed as continuous flow not only to rinse and clean but to also control for the buildup of microorganisms. Here, we evaluate a reduced water (RW) dipper well – with and without ultraviolet subtype C (UV-C) disinfection – for control and inactivation of Escherichia coli present on a stainless steel utensil. Overall, the RW dipper well (with and without UV-C) performed significantly better than the CF dipper well for removal of E. coli in 10% skim milk medium at various exposure and rinse times. More specifically, at 5, 10, and 30 s, the RW dipper well without UV-C achieved 1.04, 1.72, and 2.03 greater log₁₀ (CFU/ml) reduction in E. coli compared to the CF dipper well at the same treatment times, respectively. When combined with UV-C, the RW dipper well increased reduction of E. coli by 0.36–1.68 log₁₀ (CFU/ml) over prolonged use (i.e. 2 h continuous use). Moreover, the RW dipper well combined with UV-C may provide a preventative step to reduce the growth and/or persistence of bacteria on the utensil as well as the dipper well reservoir, especially for E. coli in 10% skim milk medium. To our knowledge this is the first study to evaluate the efficacy of dipper wells – both RW and CF systems – in the removal of E. coli on a stainless steel utensil.     

Determination of antimicrobial effect of mint and basil essential oils on survival of E. coli O157:H7 and S. typhimurium in fresh-cut lettuce and purslane

In this research, mint and basil essential oils at concentrations of 0.01 ml/L, 0.032 ml/L or 0.08 ml/L were used for disinfection treatments of fresh-cut lettuce and purslane samples inoculated with Salmonella typhimurium or Escherichia coli 0157:H7. Disinfection treatment time was applied as 10 min (short) or 15 min (long). Disinfected samples were packaged aerobically and stored at refrigerator +4 °C for 7 days. It was observed that mint and basil essential oils showed antimicrobial effect on the survival of E. coli O157:H7 and S. typhimurium inoculated into lettuce and purslane samples during refrigerated storage. Mint essential oil showed higher antimicrobial effect on pathogens when compared to basil essential oil. Mint and basil essential oils at concentration of 0.08 ml/L were the most effective antimicrobial treatment against pathogens in two different vegetable. S. typhimurium was more resistant against basil oil in lettuce samples when compared to its resistance against basil oil in purslane samples, whereas E. coli O157:H7 was more resistant to mint oil in purslane samples when compared to its resistance against mint oil in lettuce samples.