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.     

Evaluation of antimicrobial activity,probiotic properties and safety of wild strain Enterococcus faecium AQ71 isolated from Azerbaijani Motal cheese

The aims of this study were to characterize bacteriocin activity, some functional and probiotic properties, and to evaluate the safety of Enterococcus faecium AQ71 isolated from Azerbaijani Motal cheese. The studied strain inhibited the growth of selected tested LAB, Listeria monocytogenes and Bacillus cereus strains. PCR amplification with specific primers indicated that E. faecium AQ71 carry genes encoding enterocins P, L50A, L50B and A. Bacteriocin(s) produced by the studied strain was/were heat stable and active in a broad pH range. Triton X-20, Triton X-80, Triton X-100, β-mercaptoethanol, Na-EDTA, SDS and NaCl did not affect the antimicrobial activity of the strain. The cell free supernatants of the strain caused the lysis of cells of Lactobacillus brevis F145 and inhibited the growth of L. monocytogenes. E. faecium AQ71 was negative for the tested virulence factors and did not present multi-resistance to antibiotics. The strain was resistant to physiological concentrations of bile salts and showed good auto-aggregation ability as well as co-aggregation ability with L. monocytogenes. E. faecium AQ71 exhibited good esterase, esterase lipase, acid phosphatase and aminopeptidase activities.     

Enterococcus faecium LM-2, a multi-bacteriocinogenic strain naturally occurring in “Byaslag”, a traditional cheese of Inner Mongolia in China

A bacteriocin-producing strain LM-2 was isolated from “Byaslag”, a traditional cheese in Inner Mongolia of China, and identified as Enterococcus faecium. The strain produced the maximum activity of enterocin (5120 AU ml^?1) in MRS medium in the mid-stationary phase of growth (i.e. after 30 h at 37 °C). Purified enterocin LM-2 was obtained by using a two-step procedure consisting of ammonium sulfate precipitation and cation exchange chromatography. Tricine–SDS–PAGE of the purified enteriocin LM-2 contained two active protein bands between 3.5 and 6.4 kDa. It showed a broad spectrum of activity against most of the tested strains in the genera Listeria, Staphylococcus, Bacillus, Clostridium, Salmonella and Pseudomonas. All Listeria strains tested, including L. monocytogenes, were highly sensitive to this bacteriocin. The inhibitory activity of enterocin LM-2 against L. monocytogenes was bactericidal without concomitant cell growth, and the highest level of adsorption (87.5%) to the surface of L. monocytogenes 54002 cells was founded at pH 6.0. This strong inhibitory activity against L. monocytogenes, coupled with its broad pH-resistance and heat-stability indicated its potential use as a food preservative to enhance the safety of fermented foods. The presence of enterocin P and L50-like structural genes in E. faecium LM-2 was established by PCR and direct sequencing, which indicated strain LM-2 may be a new multi-bacteriocin producer strain.     

Reuterin,lactoperoxidase, lactoferrin and high hydrostatic pressure on the inactivation of food-borne pathogens in cooked ham

The antimicrobial effect of high hydrostatic pressure (HHP) processing combined with reuterin, lactoperoxydase system (LPS) and lactoferrin (LF) on the survival of Listeria monocytogenes, Salmonella enterica subsp. enterica serovar Enteritidis and Escherichia coli O157:H7 in sliced cooked ham stored under strict refrigeration temperature (4 °C) and mild temperature abuse conditions (10 °C) was investigated. One day after treatment, L. monocytogenes counts in HHP at 450 MPa for 5 min were 0.8 log units lower, but a recovery was observed with counts not significantly different to those observed in control after 35 d. S. Enteritidis and E. coli O157:H7 levels were reduced around 5 log cfu/g by the pressure treatment (450 MPa/5 min) and the numbers of these pathogens did not increase significantly during the 35 d of storage at 4 °C. The individual application of reuterin and LPS influenced the survival of the three pathogens studied, extending the lag phase of L. monocytogenes and diminishing S. Enteritidis and E. coli levels throughout storage, whereas no effect was recorded when LF was added. When reuterin or LPS were applied in combination with HHP there was a synergistic antimicrobial effect against L. monocytogenes, avoiding at 4 °C the recovery observed with individual treatments. These combined treatments also kept the levels of S. Enteritidis and E. coli O157:H7 below the detection limit (<1 log unit) in cooked ham stored at 4 and 10 °C during 35 d. The results obtained in the present work suggest that HHP at 450 MPa for 5 min in combination with LPS or reuterin would be useful as a hurdle technology approach against L. monocytogenes, S. Enteritidis and E. coli O157:H7 in cooked ham.     

Pre-processed bovine milk quality in Trinidad: Prevalence and characteristics of bacterial pathogens and occurrence of antimicrobial residues in milk from collection centres

The study was conducted to assess the impact of the changes in the milk collection system in Trinidad (from twice daily collection to once, introduction of chilling facilities to the collection centres and transportation of milk to the processing plant in insulated truck instead of in metal churns at ambient temperature) on the microbial load and antimicrobial residue quality of the milk as well as the temperature and pH of milk, using standard methods. The presence of antimicrobial residues was detected using the Delvo test kit. Of a total of 266 milk samples from churns, the mean ± sd temperature and log₁₀ ± sd TAPC per ml was 20.36 ± 7.91 °C and 6.3 ± 1.09 respectively. For 20 milk samples from the chillers, the mean temperature and log₁₀ ± sd TAPC per ml was 15.10 ± 2.73 °C and 7.04 ± 0.33 respectively compared with corresponding values for 36 samples collected from the truck, 11.64 ± 4.22 °C and 7.11 ± 0.62 respectively (P < 0.05; X²). The mean TAPC, staphylococcal and E. coli counts per ml of milk from churns were significantly (P < 0.05; X²) higher for milk at low temperature (0–20 °C) compared with milk at high temperature (>30 °C). Eight (4.2%) of 192 milk samples tested contained antimicrobial residues. Of 168 S. aureus isolates tested, 24 (14.3%) were enterotoxigenic while 53 (45.3%) of 117 isolates tested exhibited resistance to various antimicrobial agents while of 386 isolates of E. coli tested, 3 (0.8%) were O157 strain and 129 (64.5%) of 200 isolates exhibited resistance to antimicrobial agents. It was concluded that despite the changes, the microbial load of milk was still high suggesting poor sanitary practices at the farm level. The detection of antimicrobial residues agents coupled with toxigenic S. aureus and E. coli isolates could pose health hazards to consumers.     

Effects of changes in pH and temperature on the inhibition of Salmonella and Listeria monocytogenes by Allyl isothiocyanate

The minimum inhibitory (MIC) and minimum bactericidal concentrations (MBC) of mustard allyl isothiocyanate (AITC) against five strains each of Salmonella and Listeria monocytogenes individually, and when combined by genus were studied in Mueller-Hinton broth at 21 or 37 °C as well as the interactive effects of pH (5.0–9.0) at temperatures of 4–21 °C on cell viability when held under these conditions for up to 10 d. The stability of 200 ppm AITC was monitored during these trials. The MIC and MBC values of AITC ranged from 60 to 100 ppm and 120–180 ppm, respectively, at 37 °C and ranged from 10 to 40 ppm and 200–600 ppm, respectively, at 21 °C against both pathogens. AITC had no antimicrobial activity at low temperatures (4 or 10 °C) and alkaline pH over 10 d, but at neutral pH, AITC reduced L. monocytogenes by 4.14 and 8.45 log₁₀ CFU/ml at 4 or 10 °C, respectively. At acidic pH, AITC was more effective against Salmonella which was reduced by 2.56 and 6.48 log₁₀ CFU/ml at 4 and 10 °C, respectively. However, AITC was more effective at combinations of 21 °C and neutral pH against L. monocytogenes (cells were not detected at and beyond 3 d) and at combinations of the higher temperature and acidic pH against Salmonella (cells were not detected at and beyond 6 d). Mustard AITC was more stable at low pH and temperature indicating that it can be an effective antimicrobial at combinations of low or neutral pH values and room or refrigerator temperatures (4–10 °C) against these foodborne pathogens.     

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.     

Stilbene phytoallexins inclusion complexes: A natural-based strategy to control foodborne pathogen Campylobacter

Due to the highly epidemic character of Campylobacter infections and to the increased antibiotic resistance of these microorganisms, new approaches to control them are highly demanded. In this work, we investigated the anti-Campylobacter activity and mode of action of stilbenes encapsulated in cyclodextrins. Results showed that pterostilbene and pinosylvin and their inclusion complexes (ICs) had antimicrobial activity against Campylobacter jejuni and Campylobacter coli. Furthermore, pinosylvin ICs had a bactericidal activity against both Campylobacter species at 37 °C and even at 4 or 20 °C. This bactericidal action is due to membrane damage, resulting in the impairment of several cellular functions such as membrane polarization, permeability and efflux activity. This is the first study describing the antimicrobial activity of stilbenes and their inclusion complexes against Campylobacter spp. and the results obtained encourage the use of pinosylvin as a preservative for the effective control of Campylobacter in foods.     

Antimicrobial action and effects on beef quality attributes of a gaseous ozone treatment at refrigeration temperatures

The effects of gaseous ozone treatment at refrigeration temperatures, on microbial counts (total aerobic mesophilic heterotrophic microorganisms and inoculated Escherichia coli) in culture media and in beef samples were analyzed. The influence of ozone on beef quality properties such as surface color and rancidity was measured.The effect of gaseous ozone (154 × 10^?6 kg m^?3) in culture media inoculated with E. coli after 3- or 24-h treatment at 0° and 4 °C caused a total inactivation of this microorganism.For beef samples treated with the same gaseous ozone concentration, the highest microbial inhibition was observed at 0 °C and after 24-h exposure, producing a decrease of 0.7 and 2.0 log₁₀ cycles in E. coli and total aerobic mesophilic heterotrophic microorganism counts respectively; however, both the surface color and lipid oxidation of these beef samples were unacceptable. Shorter exposure times (3 h) to the tested ozone concentration at both temperatures (0–4 °C), reduced 0.5 log₁₀ cycles the counts of total aerobic mesophilic heterotrophic microorganisms and 0.6–1.0 log₁₀ cycles the counts of E. coli, without changing the color or producing rancidity in beef.     

Effect of organic acids,hydrogen peroxide and mild heat on inactivation of Escherichia coli O157:H7 on baby spinach

Minimally processed baby spinach contaminated with Escherichia coli O157:H7 has been associated with multiple outbreaks of foodborne illnesses recently. Chlorinated water is widely used to wash vegetables commercially, but this washing procedure has limited efficacy and can lead to the formation of carcinogenic substances. This study was conducted to determine the effects of organic acids and hydrogen peroxide alone and in binary combinations with or without mild heat (40 and 50 °C) on the inactivation of Escherichia coli O157:H7 on baby spinach. Baby spinach leaves were dip-inoculated with E. coli O157:H7 to a level of 6 log CFU/g and stored at 4 °C for 24 h before treatment. Individual washing solutions (1% and 2% lactic acid [LA], citric acid [CA], malic acid [MA], tartaric acid [TA], acetic acid [AA], hydrogen peroxide [H₂O₂] as well as binary combinations of LA, CA, MA and H₂O₂ at final concentrations of 1% were used to decontaminate spinach leaves at 22, 40 or 50 °C for 2–5 min to test their efficacy in reducing E. coli O157:H7. Chlorinated water (200 ppm free chlorine) decreased the population of E. coli O157:H7 on baby spinach by only 1.2–1.6 log CFU/g, which was not significantly different from DI water washing. Washing with 1% LA at 40 °C for 5 min was the most effective treatment achieving a 2.7 log reduction of E. coli O157:H7 which is significantly higher than chlorine washing. Washing with LA + CA or LA + HP at 40 °C for 5 min was equally effective against E. coli O157:H7, resulting in a 2.7 log reduction of E. coli O157:H7. The application of mild heat significantly enhanced the efficacy of washing solutions on the inactivation of E. coli O157:H7. There was, however, no significant difference between treatments at 40 °C for 5 min and 50 °C for 2 min. The results suggested that the use of organic acids in combination with mild heat can be a potential intervention to control E. coli O157:H7 on spinach.     

Characterization of bacPPK34 a bacteriocin produced by Pediococcus pentosaceus strain K34 isolated from “Alheira”

Different lactic acid bacteria were isolated during different stages in the production of “Alheiras”, a traditionally fermented sausage produced in the north of Portugal, between 2005 and 2007, in a total of 484 isolates. One of 484 isolates (K34) produced a bacteriocin, designated as bacPPK34, and was identified as a strain of Pediococcus pentosaceus by 16S rRNA sequencing. The highest bacteriocin production was noted at late log/early stationary phase after 15–18 h of growth in MRS broth at 37 °C (3200 AU/ml) against Enterococcus faecalis ATCC 29212 and 12800 AU/ml against Listeria monocytogenes (L1, L2, L3). bacPPK34 was between 2.5 kDa and 6.2 kDa in size, as determined by tricine-SDS-PAGE. Complete inactivation or significant reduction in antimicrobial activity was observed after treatment of cell-free supernatants with proteinase K, pepsin and trypsin. No change in activity was recorded when treated with catalase. The bacteriocin was resistant to treatments with lipase and detergents Triton X-100, Tween 20, SDS, NaCl, urea and EDTA. Furthermore, the bacteriocin remained active after 2 h at pH 2–12 and temperature treatments at 60, 80, 100 °C, 1 month of storage at ?20 and 4 °C and 20 min at 121 °C. Addition of bacPPK34 to a mid-log culture of L. monocytogenes and E. faecalis ATCC 29212 inhibited growth. The bacteriocin did not adhere to the surface of the producer cells.     

Effects of Quillaja saponaria extract and Nα-lauroyl-l-arginine ethyl ester on reducing selected foodborne pathogens in vitro and maintaining quality of fresh-cut endive (Cichorium endivia L.) at pilot plant scale

The aim of the present study was to evaluate the applicability of Quillaja saponaria extract (QSE) and N^α-lauroyl-l-arginine ethyl ester (LAE) as antimicrobial wash water additives in fresh-cut lettuce processing. Antibacterial activities of LAE and QSE against selected strains of the foodborne pathogens Salmonella enterica, Bacillus cereus, Staphylococcus aureus, Pseudomonas aeruginosa, and Listeria monocytogenes were examined in vitro. Minimum inhibitory concentrations determined by broth microdilution assay demonstrated that LAE exhibited a strong antimicrobial activity with MICs between 4 and 32 μg/mL against all tested strains, whereas QSE showed a weaker antimicrobial activity with MICs >512 μg/mL. On a pilot-plant scale, the effects of warm water washing at 45 °C for 120 s with and without 40 mg/L QSE or 100 mg/L LAE as well as cold water washing at 4 °C for 120 s with QSE or LAE, respectively, of shredded endive (Cichorium endivia L.) were investigated regarding microbiological and sensory quality as well as physiological properties. Samples were analyzed for headspace O₂ and CO₂ levels, phenylalanine-ammonia-lyase activity and contents of nitrite and nitrate during nine days of cold storage at 4 °C. By analogy to its antimicrobial effect against the foodborne pathogens in vitro, LAE allowed up to 4 log₁₀ cfu/mL reduction of the microbial load in the washing water of the pilot plant, and might therefore reduce cross-contamination while saving water. The addition of LAE to warm washing water impaired sensory properties of fresh-cut endive during storage, which was predicted by chlorophyll fluorescence imaging analyses. QSE treatment combined with warm water washing best retained sensory appearance throughout our study, being possibly suitable for the production of premium products.     

Antimicrobial activity of açaí against Listeria innocua

A study was carried out to evaluate antimicrobial activity of açaí against Listeria innocua, as a non-pathogenic surrogate for Listeria monocytogenes, at different temperatures (37, 22, and 10 °C), from a kinetic point of view. With this aim, first the Minimum Inhibitory Concentration (MIC) under optimal growth conditions was established (37 °C), and then the effect of 3 non-inhibitory doses (3, 5, and 7 g/L) at 37, 22, and 10 °C was evaluated on the basis of the kinetic parameters lag time (λ) and maximum specific growth rate (μ_max). The Total Phenolic Content (TPC) of the samples tested as a function of açaí concentration was also determined. Results obtained showed that the MIC was 10 g/L, containing 2154.91 ± 126.10 mg of Gallic Acid Equivalents (GAE)/L. At non-inhibitory doses, regardless of temperature, the higher the açaí concentration, the higher the value of λ, and the effect of a variation in açaí concentration on λ was greater at high temperatures. Therefore, the addition of non-inhibitory doses of açaí could provide a means of controlling the growth of L. monocytogenes if a cold chain failure occurs, or if any other reason compromises the microbiological safety of minimally processed foods. Consequently, the present study is important both for the science community and for the food industry because it provides the first mathematical characterization of açaí antimicrobial activity and reveals its potential use to control the concentration and growth of pathogenic bacteria in foods free of non-synthetic additives.     

Antimicrobial activity of polysaccharide films containing essential oils

Antimicrobial films were prepared by incorporating different concentrations of bergamot (BO), lemon (LO) and tea tree (TTO) essential oils (EO), into chitosan (CH) and hydroxypropylmethylcellulose (HPMC) films. Their antibacterial effectiveness against Listeria monocytogenes, Escherichia coli and Staphylococcus aureus was studied at 10 °C during a storage period of 12 days. HPMC-EO and CH-EO composite films present a significant antimicrobial activity against the three pathogens considered. The nature and amount of the essential oils (EO), the structure of the film and the possible interactions which exist between the polymers and active constituents of EO affected the antimicrobial activity of the films. In all film matrices, TTO exhibited the highest antimicrobial activity. A complete inhibition of microbial growth was observed for CH or HPMC-TTO films for E. coli, HPMC-TTO for L. monocytogenes and HPMC-BO for S. aureus.     

Effectiveness of several chemical decontamination treatments against Gram-negative bacteria on poultry during storage under different simulated cold chain disruptions

Five chemical compounds – 12% trisodium phosphate (TSP), 1200 ppm acidified sodium chlorite (ASC), 2% citric acid (CA), 220 ppm peroxyacids (PA) and 50 ppm chlorine dioxide (CD) – were analyzed to determine their effectiveness against Gram-negative bacteria (Salmonella enterica serotype Enteritidis, Yersinia enterocolitica, Escherichia coli and Pseudomonas fluorescens) artificially inoculated on skinless chicken legs. Samples were stored for 120 h under three different simulated cold chain disruptions: T1 (12 h at 1 ± 1 °C, followed by 6 h at 15 ± 1 °C and then 102 h at 4 ± 1 °C), T2 (18 h at 1 ± 1 °C, 6 h at 15 ± 1 °C and 96 h at 10 ± 1 °C) or T3 (18 h at 4 ± 1 °C, 6 h at 20 ± 1 °C and 96 h at 7 ± 1 °C). Microbiological analyses and pH determinations were carried out at 0, 24, 72 and 120 h of storage. TSP, ASC and CA significantly (P < 0.05) reduced microbial populations, relative to control (untreated) samples. TSP and ASC caused higher (P < 0.05) reductions of S. enterica than CA under moderate temperature abuse conditions (T2 and T3). TSP and ASC (T2) or TSP and CA (T1 and T3) were the most effective compounds against E. coli. TSP and ASC showed the highest antimicrobial effect (P < 0.05) at mild temperature abuse conditions (T1) for Y. enterocolitica, while ASC was the most active compound against this pathogen under T2 and T3 conditions. TSP caused the largest average reductions of Ps. fluorescens at T1. PA and DC originated scant microbial reductions under all of the conditions proposed. These findings extend current knowledge about these chemical decontaminants, and may help the Regulatory Authorities in their decisions about the poultry decontamination authorization process within the European Union.     

Changes in resistance of Salmonella Typhimurium biofilms formed under various conditions to industrial sanitizers

The aim of this study was to understand how different factors including biofilm age, attachment surface (stainless steel and acrylic) and various growth conditions such as different pH (pH 6 and 7) and temperature (28, 37 and 42 °C) affected the resistance of Salmonella Typhimurium biofilm against industrial sanitizers. The sanitizers tested were quaternary ammonium compounds (QAC, 200 ppm), mixed peroxyacetic acid/organic acids (PAO, 0.1%) and sodium hypochlorite (chlorine, 50 ppm). It was observed that, for biofilms formed at pH 7–37 °C, chlorine was the most effective sanitizer, followed by QAC and PAO. For all conditions tested, attachment surfaces didn't cause any significant difference in biofilm resistance against sanitizers. Increasing biofilm age led to an increase in resistance to sanitizers, although such effect was growth condition- and sanitizer-dependent. The resistance of biofilm formed on stainless steel at pH 6–37 °C increased with increasing biofilm ages. The effect of temperature and pH on biofilm resistance was dependent on biofilm ages. For 168-h biofilm formed at pH 6, the resistance to all three sanitizers was highest for 37 °C, followed by 28 and 42 °C; while biofilm formed at 37 °C for 168 h, pH 6 condition increased biofilm resistance to QAC and PAO, but not chlorine, compared with pH 7. These results indicate that the resistance of biofilms against sanitizers was dependent on biofilm age, temperature, and pH.     

Antimicrobial activities of red wine-based formulations containing plant extracts against Escherichia coli O157:H7 and Salmonella enterica serovar Hadar

We evaluated the antimicrobial activities of three red wine based plant extract/plant essential oil (EO) formulations: olive extract powder/oregano EO, apple skin extract powder/lemongrass EO, and green tea extract powder/bitter almond EO, and their formula permutations against the foodborne pathogens Escherichia coli O157:H7 and Salmonella enterica serovar Hadar. The following parameters that were expected to affect antimicrobial activity were evaluated: pH (3.6 or 7.0), temperature (4, 22, and 37 °C), incubation time (0, 5, 30, and 60 min) and bacterial load (∼10⁴ or ∼10⁹ bacteria/ml). The formulations with oregano, lemongrass, or bitter almond EO inhibited the growth of both pathogens at acidic pH with bacterial loads of ∼10⁴ or ∼10⁹ bacteria/ml. At neutral pH, the formulations were less effective. Although all the 3-component formulations were fast acting; showing significant activity in less than 5 min, only the activity of the lemongrass-containing formulation markedly increased with longer incubation times from 0 to 60 min. Activity also increased for all 3-component formulations with increasing temperature from 4 °C to 37 °C, although the activity of the lemongrass formulation appeared to level off at 22 °C. Of the tested formulations, the lemongrass EO formulations, at pH 3.6, appeared to be the most effective against the tested pathogens, especially against Salmonella. The most active formulations merit evaluation for antimicrobial efficacy in liquid and solid food.     

Inhibition of Listeria monocytogenes in vitro and in goat milk by liposomal nanovesicles containing bacteriocins produced by Lactobacillus sakei subsp. sakei 2a

Lactobacillus sakei subsp. sakei 2a is a bacteriocinogenic lactic acid bacteria isolated from a Brazilian meat product, capable to inhibit Listeria monocytogenes in vitro and in foods. In this study, bacteriocin produced by this strain were encapsulated in phosphatidylcholine (FC) and 1,2-dioleoyloxy-3-trimethylammonium-propane (DOTAP) liposomes, separately and in combination, were characterized and evaluated for activity against L. monocytogenes in vitro and in experimentally contaminated UHT goat milk, during storage at 7 °C for 14 days and 30 °C for 24 h. The FC and DOTAP/FC (3:1) nanovesicles containing bacteriocins (12.800 AU mL⁻¹) presented zeta potential of −1.54 and + 38.13 mV, Entrapment Efficiency of 80.0% and 94.1%, and diameter of 91.19 and 81.49 nm, respectively. DOTAP/FC nanovesicle presented excellent stability, and maintained the same physicochemical characteristics over 28 days. Both free and encapsulated bacteriocins controlled L. monocytogenes growth in BHI medium and goat milk stored at 30 °C for at least 8 h, in a similar pattern. After 24 h in BHI medium, bacteriocins encapsulated in FC nanovesicles were more effective (p < 0.05) than free bacteriocins. However, in goat milk, no significant differences (p ≥ 0.05) were observed for the two types of nanovesicles. At 7 °C, both free and encapsulated bacteriocins retarded the L. monocytogenes growth, and after 5 days, counts were 5 log lower than in the controls, both in BHI and in goat milk. Encapsulation of bacteriocin in FC and DOTAP/FC nanovesicles did not affect the antimicrobial activity, but the advantages of their application for control of L. monocytogenes in goat milk based dairy products, when compared to free bacteriocins, remain unclear and more studies are needed.     

Adherence of cold-adapted Escherichia coli O157:H7 to stainless steel and glass surfaces

The effects of previous cold-induced cell elongation on adherence of Escherichia coli O157:H7 to glass slides and stainless steel surfaces was evaluated at 4 °C for ≤48 h. Planktonic E. coli O157:H7 with and without cold adaptation were prepared at 15 and 37 °C, respectively, and planktonic E. coli O157:H7 containing elongated (>4 ≤ 10 μm) and filamentous (>10 μm) cells were prepared at 6 °C. Despite morphological differences in planktonic E. coli O157:H7 preparations, all three cell types attached to a greater extent to glass than to the stainless steel surfaces. E. coli O157:H7 cells adapted to growth at 15 °C attached better to both glass and stainless steel surfaces (3.2 and 2.6 log cfu/cm², respectively) than cells of the other treatments at ≥24 h. Cells adapted at 6 °C attached to glass slides and stainless steel coupons at levels of 3.0 and 1.8 log cfu/cm², respectively, while E. coli O157:H7 cells grown at 37 °C attached to these surfaces at levels of 2.0 and 1.7 log cfu/cm², respectively. No further attachment of cells from any of the treatments was noted between 24 and 48 h at 4 °C. These results suggest that E. coli O157:H7 cells adapted at 6 °C–15 °C have greater potential to attach to food contact surfaces than those grown at higher temperature. The enhanced biofilm-forming ability of 6 °C or 15 °C-adapted, elongated and filamentous E. coli O157:H7 cells did not appear to be related to the greater entanglement of longer cells within biofilm matrices.