Antimicrobial efficacy of cinnamon oil against Salmonella in almond based matrices

Reduced moisture enhances resistance of Salmonella and subsequently reduces the antimicrobial efficacy of thermal treatment. Alternative and supplementary non-thermal intervention methods are urgently needed. In this study, Cinnamonum cassia oil was tested for its antimicrobial effect against outbreak strains Salmonella Enteritidis PT30 and S. Tennessee K4643. Minimal inhibitory concentration and minimal bactericidal concentration for both strains were 0.05% (v/v) and 0.1% (v/v), respectively. Death curves showed that including 0.1% and 0.15% (v/v) C. cassia oil resulted in ∼7 Log reduction of bacteria within 2 h and 1 h, respectively. However, the antimicrobial efficacy of C. cassia oil was reduced when S. Enteritidis PT30 existed in low moisture condition. When S. Enteritidis PT30 was established on almonds/paper discs, 0.4% C. cassia oil resulted in ∼1.7 Log₁₀ CFU/almond or 3.2 Log₁₀ CFU/disc reduction within 2 h at room temperature, respectively. S. Enteritidis PT30 established on both almonds and paper discs were very stable, there was only a 0.80 Log₁₀ CFU/almond and 1.20 Log₁₀ CFU/disc reduction during 9-week and 7-week storage at room temperature, respectively. C. cassia oil intervention increased S. Enteritidis PT30 reduction on both almonds and paper discs during storage with more reduction on paper discs. 0.4% C. cassia oil treatment reduced S. Enteritidis PT30 on paper disc to undetectable level within 4 weeks, but only led to 2 Log₁₀ CFU reduction on almonds, indicating a protection effect from the almond matrix or almond surface components. Additionally, S. Enteritidis PT30 established on paper disc coated with almond surface components exhibited higher resistance to desiccation and C. cassia oil treatment, further demonstrating the protection role of food matrix. In conclusion, C. cassia oil is effective against S. Enteritidis PT30 and S. Tennessee K4643, but its antimicrobial efficacy against the tested Salmonella was compromised by low moisture environment and food matrix.     

Inhibitory effect of Cinnamomum cassia oil on non-O157 Shiga toxin-producing Escherichia coli

Shiga toxin-producing Escherichia coli (STEC) have caused numerous foodborne outbreaks. Compared with the most well-known STEC E. coli O157:H7, importance of non-O157 STEC has been underestimated and they have gained far less attention till increasing outbreaks recently. Using natural plant materials as antimicrobial agents is a heated area. Therefore in this study, Cinnamomum cassia, a widely used spice in cuisine, was tested for its antibacterial efficacy on CDC “top six” non-O157 STECs including O26, O45, O103, O111, O121, O145. Gas chromatography-mass spectrometry analysis showed that the major component of C. cassia oil was cinnamaldehyde (59.96%). The disk diffusion assay indicated that 20 μL 4% (v/v) C. cassia oil per disk resulted in inhibition zones of 15.0 mm, 18.5 mm, 15.7 mm, 19.3 mm, 18.8 mm, and 25.3 mm for O26:H11, O45:NM, O103:H2, O111:H2, O121:H19, and O145:NT, respectively. Minimum inhibitory concentration for all tested non-O157 STECs were 0.025% (v/v). Minimum bactericidal concentration was strain dependent, which was 0.05% (v/v) for O26:H11, O121:H19, O145:NT, while 0.1% (v/v) for O45:NM, O103:H2 and O111:H2. Growth kinetics showed that at the low inoculation of approximate 2.5 × 10⁵ CFU/mL, C. cassia oil at the concentration of 0.01875% (v/v) completely inhibited the growth of O26:H11 and O145:NT for at least 24 h, and increased the duration of lag phase of O45:NM, O103:H2, O111:H2, O121:H19 by18, 12, 6, and 16 h, respectively. Including 0.025% (v/v) C. cassia oil completely inhibited the growth of all tested non-O157 STECs for at least 24 h. At high inoculation of 5 × 10⁶ CFU/mL, inhibition effect of C. cassia oil decreased. Death curve showed that including as low as 0.05% (v/v) C. cassia oil could kill non-O157 STECs. 0.1% (v/v) C. cassia oil showed bactericidal effects on all tested non-O157 STECs within 15 min. C. cassia oil at the concentration of 0.15% (v/v) killed all O26:H11, O121:H19 and O145:NT within 30 min, while O45:NM, O103:H2 and O111:H2 at 120, 60, and 60 min, respectively. In conclusion, C. cassia oil can effectively inhibit the growth of non-O157 STECs at concentration as low as 0.025% (v/v). Our data suggest that C. cassia oil has the potential to be used as a natural antibacterial agent in food industry.     

Antibacterial activity and mechanism of cinnamon essential oil against Escherichia coli and Staphylococcus aureus

Cinnamon essential oil (EO) exhibited effective antibacterial activity against foodborne spoilage and pathogenic bacteria in model systems using Escherichia coli and Staphylococcus. The minimum inhibition concentration (MIC) of cinnamon EO was similar for both bacteria (1.0 mg/ml) while the minimum bactericide concentration (MBC) were 4.0 mg/ml and 2.0 mg/ml for E. coli and Staphylococcus aureus. GC–MS analysis confirmed that cinnamaldehyde was the major constituent in cinnamon EO (92.40%). Much effort was focused on elucidating the mechanism of antibacterial action of cinnamon EO against E. coli and S. aureus by observing the changes of cell microstructure using scanning electron microscope, determination of cell permeability, membrane integrity and membrane potential. After adding cinnamon EO at MIC level, there were obvious changes in the morphology of bacteria cells indicating cell damage. When cinnamon EO were added at MBC levels, the cells were destroyed. Cinnamon EO led to leakage of small electrolytes, causing rapid increase in the electric conductivity of samples at the first few hours. The values for E. coli and S. aureus reached 60% and 79.4% respectively at 7 h. Moreover, the concentration of proteins and nucleic acids in cell suspension also rose with increased cinnamon EO. Bacterial metabolic activity was decreased 3–5 folds as reflected by the results of membrane potential. Overall, S. aureus was more susceptible to cinnamon EO than E. coli.     

The specific antibacterial activity of liposome-encapsulated Clove oil and its application in tofu

In this study, the antibacterial activities of Clove oil and liposome-encapsulated Clove oil were investigated. First, the antibacterial activity of Clove oil demonstrated that the essential oil exhibited favorable antimicrobial activity for both Escherichia coli and Staphylococcus aureus. However, a setback of using Clove oil as a disinfectant is its low chemical stability. Then Clove oil was incorporated into a liposome formulation to increase its stability. The optimal polydispersity index (PDI) (0.196), Zeta potential (−24.5 mV) and entrapment efficiency (20.41%) of liposome were obtained at the concentration of Clove oil to 5.0 mg/mL. In addition, selective antimicrobial activity for S. aureus by utilizing pore-forming toxins (PFTs) to activate Clove oil release from liposome was observed. By contrast, liposome-encapsulated Clove oil has no effect on E. coli that doesn't secrete PFTs because antimicrobial component can't reach bacteria. Gas chromatography (GC) assay found that when liposome met S. aureus that secrete PFTs, PFTs would insert into the liposome membranes and form pores, through which the encapsulated Clove oil was released. Besides, liposome-encapsulated Clove oil exhibited efficient antimicrobial activity for S. aureus in tofu.     

Antimicrobial resistance of Escherichia coli and Staphylococcus aureus isolated from food handler's hands

The aim of this study was to determine the antimicrobial resistance of Escherichia coli and Staphylococcus aureus isolates from food handlers' hands at primary schools in Hulu Langat district, Selangor (Malaysia). Disc diffusion methods were used to examine the antimicrobial resistance of the bacteria by using ten types of antibiotic discs with different concentrations. The results show that the prevalence of S. aureus (65.88–74.12%) was far higher than the prevalence of E. coli (9.41–14.12%). The percentage isolates of E. coli that were resistant to the antibiotics was 85.71% Penicillin and Chloramphenicol, 57.14% Sulfamethoxazole-Trimethoprim, Ampicillin and Trimethoprim, 28.57% Kanamycin and Tetracycline and 14.29% Ciprofloxacin. All of the isolates had shown susceptible to Gentamicin and Nitrofurantoin. For S. aureus, the percentage isolates that were resistant to the antibiotics was 72.30% Ampicillin, 53.38% Penicillin, 4.73% Nitrofurantoin,1.35% Chloramphenicol and Trimethoprim and 0.68% Kanamycin and Tetracycline. None of the isolates had shown resistant to Ciprofloxacin, Sulfamethoxazole-Trimethoprim and Gentamicin. Multidrug resistant Escherichia coli represented a high percentage (85.71%) of the total positive strains revived whereas multidrug resistant S. aureus strains were only 5.41% of the total positive strains. The existence of multidrug resistant bacteria is quite worrying as they may pose serious threat to the patients. Hence, the microbiological quality of food handlers' hands from foodservice operations should be maintained in a good condition to reduce the existence of multidrug resistance bacteria.     

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.     

Rutin inhibits mono and multi-species biofilm formation by foodborne drug resistant Escherichia coli and Staphylococcus aureus

Considering the role of biofilm in food spoilage and the food industry, inhibition of biofilm formation by natural agents is expected to be safe and could also enhance the efficacy of other antimicrobial strategies for controlling microbial food spoilage. Plant flavonoids are known for their diverse biological activity including antimicrobial. Therefore, rutin was investigated for its biofilm inhibitory activity at sub-minimum inhibitory concentrations (sub-MICs) values against common foodborne pathogens (Escherichia coli and Staphylococcus aureus). Minimum inhibitory concentrations (MIC) ranged from 400 to 1600 μg/ml against the selected strains. Sub-MICs (1/16 × MIC to 1/2 × MIC) were used to assess the inhibition of biofilm formed by E. coli and S. aureus in microtitre plate assay. Mono strain biofilm formation by Escherichia coli and Staphylococcus aureus was greatly reduced by rutin at their respective 1/2 × MIC. For multi-species (E. coli: and S. aureus) biofilm formation, the reduction in biofilm production was concentration dependent. No significant bacteria mass reduction was recorded for any sub-MIC. SEM images of biofilm inhibition on steel chips confirmed the reduction in number of microcolonies. Exopolysaccharide production responsible for adherence and maturation of biofilms was also significantly (p ≤ 0.05) reduced at respective concentrations of rutin in tested strains. To the best of our knowledge, this is the first study describing the effect of flavonoid, rutin on multi-species biofilms consisting of S. aureus and E. coli. Findings of the study indicate a potential application of rutin in the prevention of biofilm on industrial equipment and food contact surfaces and prevent food contamination and spoilage.     

Combined antimicrobial effect of high pressure processing and ethyl lauroyl arginate (LAE)-containing films and its application in coconut water preservation

The combined effect of high pressure processing (HPP) and antimicrobial film enriched with ethyl lauroyl arginate (LAE) was investigated. More than 5 log₁₀ CFU/mL reduction of Staphylococcus aureus and Escherichia coli O157:H7 were achieved at 300 MPa HPP combined with 2.0% LAE-PLA film. HPP combined with LAE-PLA film showed a synergistic inactivation against S. aureus, probably because it severely damaged the cell membrane and eliminated pressure-induced sublethal injuries of S. aureus. However, no synergistic effect between HPP and LAE-PLA film was found on E. coli O157:H7. Furthermore, coconut water under 300 MPa HPP with 2.0% LAE-PLA treatment showed a longer shelf life than that of 500 MPa HPP alone. These results indicated that antimicrobial films could serve as a promising hurdle technology to lower the processing intensity of HPP while maintaining safety.     

Adhesion of Staphylococcus aureus and Staphylococcus xylosus to materials commonly found in catering and domestic kitchens

The aim of this work was to investigate the adhesion of Staphylococcus aureus and Staphylococcus xylosus on marble, granite, polypropylene, stainless steel 304 and stainless steel 316. The results showed that S. aureus adhered to all substratums. The maximum was observed on marble (30 10⁶ CFU/cm²) and, on polypropylene (30,2 10⁶ CFU/cm²). The results showed also that S. xylosus revealed a high ability to adhere to all substratum. This strains adhere more on marble (32.8 10⁶ CFU/cm²) and granite (16,3 10⁶ CFU/cm²) than to others substratum. The highest extent of adhesion of S. aureus and S. xylosus occurred to marble, polypropylene and granite. A correlation between substratum physicochemical properties and bacterial adhesion was also examined. A good correlation was observed between S. xylosus adhesion and their acid-base character. The topography of substratum surface was investigated using AFM. A good correlation was obtained between roughness and bacterial adhesion.     

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.     

Antimicrobial activity of malic acid against Listeria monocytogenes,Salmonella Enteritidis and Escherichia coli O157:H7 in apple,pear and melon juices

Minimal inhibitory (MIC) and minimal bactericidal (MBC) concentrations of malic acid against Listeria monocytogenes, Salmonella Enteritidis and Escherichia coli O157:H7 inoculated in apple, pear and melon juices stored at 5, 20 and 35 °C were evaluated. MICs and MBCs against L. monocytogenes, S. Enteritidis and E. coli O157:H7 were significantly affected by storage temperature, juice characteristics and type of microorganism. Malic acid was more effective at 35 and 20 °C than at 5 °C in all studied fruit juices. E. coli O157:H7 was more resistant to malic acid than S. Enteritidis and L. monocytogenes. Apple, pear and melon juices without malic acid were inhibitory to E. coli O157:H7, S. Enteritidis and L. monocytogenes at 5 °C, whereas, MBCs of 1.5% (v/v) of malic acid in apple and pear juices, and 2% (v/v) in melon juice at 5 °C were needed to reduce E. coli O157:H7, those concentrations being higher than those required to reduce S. Enteritidis and L. monocytogenes in those fruit juices. In addition, concentrations of 2%, 2.5% and 2.5% (v/v) of malic acid added to apple, pear and melon juices, respectively, were required to inactivate the three pathogens by more than 5 log cycles after 24 h of storage at 5 °C. Transmission electron microscopy showed that malic acid produced damage in the cell cytoplasm of pathogens without apparent changes in the cell membrane.     

Chemical composition,antibacterial activity of Cyperus rotundus rhizomes essential oil against Staphylococcus aureus via membrane disruption and apoptosis pathway

The chemical composition, antibacterial activity and mechanism of essential oil from Cyperus rotundus rhizomes against Staphylococcus aureus were investigated in this study. Results showed that α-cyperone, cyperene and α-selinene were the major components of the essential oil. The essential oil exhibited strong antibacterial activity against S. aureus with the minimum inhibitory concentration (MIC) and minimum bactericide concentration (MBC) were 10 and 20 mg/mL respectively, and the antibacterial effects increased with increasing essential oil concentrations and treatment time. The electric conductivity, cell membrane integrity, NPN uptake, and membrane potential assays demonstrated that essential oil disrupted the membrane integrity of S. aureus. Electron microscope observations further confirmed that essential oil destroyed cell membrane. Moreover, we found that essential oil could induce cells death of S. aureus through apoptosis pathway based on apoptosis analysis. These findings suggested that essential oil mainly exerted antibacterial activity by damaging cell membrane and membrane-mediated apoptosis pathway.     

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.     

Prevalence of foodborne pathogens in Turkish Van otlu (Herb) cheese

The survey was conducted on 50 unripened Van otlu cheese samples obtained in Van and Hakkari markets at retail level to determine the microbial characteristics with special emphasis on Staphylococcus aureus, Escherichia coli, E. coli O157:H7 and Salmonella spp. The results revealed that S. aureus and E. coli were present in extremely high numbers, with a mean 6.10 and 3.68 log CFU/g, respectively. S. aureus was found in all samples ranging from 2.48 to 7.15 log CFU/g and was present in more than 5.0 × 10⁵ CFU/g in 54% of the samples whereas E. coli was found in 62% of the samples. None of the samples contained E. coli O157:H7; but 3 of the 50 samples had Salmonella spp. The results indicate that Van otlu cheese presents a potential hazard for public health; and the necessary precaution will have to be taken to improve the sanitary practices and cheese manufacturing technique.     

Mechanism of the combined anti-bacterial effect of green tea extract and NaCl against Staphylococcus aureus and Escherichia coli O157:H7

The mechanism of the combined anti-bacterial effect of green tea extract (GTE) and NaCl against Staphylococcus aureus NBRC 13276 and Escherichia coli O157:H7 was investigated. After treatment for 1 h, GTE was more effective against S. aureus than E. coli O157:H7, and combined GTE/NaCl treatment caused greater cellular damage in S. aureus NBRC 13276, where it was bactericidal, than E. coli O157:H7. Compared to treatment with 1.0 mg/mL GTE, which had no effect on the survival rate of E. coli O157:H7 after 48 h, treatment with 4% NaCl alone caused greater cellular damage. Moreover, bacteria pretreated with NaCl showed delayed growth in the presence of GTE. It is therefore likely that susceptibility of E. coli O157:H7 to GTE was increased by exposure to NaCl. E. coli O157:H7 pretreated with GTE and NaCl did not multiply in the presence of GTE. Visualization of the catechin components of GTE-treated bacteria using an electron microscope and SDS-PAGE analysis of cell proteins showed that GTE attached to proteins on the surface of the bacteria to form high-molecular weight complexes, suggesting the possibility that GTE inhibits the uptake and secretion of substrates and inhibits enzyme activity. Notably, after the GTE treatment for 1 h, both bacterial strains suffered injury but recovered by cultivation in rich medium. The damage and aggregation of proteins caused by GTE treatment were repaired upon treatment with LP diluent.     

Effects of cinnamaldehyde on Escherichia coli and Staphylococcus aureus membrane

Gram-negative Escherichia coli (ATCC 8735) and Gram-positive Staphylococcus aureus (ATCC 3101) were selected as model bacteria to determine the antimicrobial mechanism of cinnamaldehyde. Several techniques were utilized to investigate the effects of cinnamaldehyde on food-borne bacterial membranes. The ultraviolet (UV) absorption and electrical conductivity of the culture supernatant were used to determine membrane integrity. β-Galactosidase activity was determined to detect inner membrane permeability. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were performed to observe bacterial morphology. Samples from both strains exposed to cinnamaldehyde showed higher UV absorptions, conductivity values, and β-Galactosidase activities compared with the control group and displayed a rapid rise trend. Thereafter, the values stabilized at a relatively steady state. SEM shows that treated E. coli and S. aureus cell samples exhibited rough cell membranes with particulate matter, and some of the S. aureus cells split due to deep wrinkle formation and distortion, unlike the control group. TEM shows that the bacteria treated with cinnamaldehyde exhibited numerous abnormalities, including cytoplasmic membrane separation from the cell wall, cell wall and cell membrane lysis, cytoplasmic content leakage, cytoplasmic content polarization, cell distortion, and cytoplasmic content condensation. These results indicate that bacterial cell morphology, membrane integrity, and permeability are damaged when the E. coli and S. aureus cells are exposed to the minimum inhibitory concentrations of cinnamaldehyde (0.31 mg/mL). In addition, the higher the cinnamaldehyde concentration, the more serious the bacterial membrane damage is.     

Essential oil composition and antimicrobial activity of Sphallerocarpus gracilis seeds against selected food-related bacteria

Sphallerocarpus gracilis from China is a little-investigated edible and medicinal plant. In the present study, the essential oil composition from S. gracilis seeds was investigated by GC and GC–MS. A total of 34 compounds representing 94.69% of the essential oil were tentatively identified. The main constituents were p-cymene (17.42%), γ-terpinene (25.58%) and α-asarone (33.12%). The antimicrobial activity, minimum inhibitory concentration (MIC), and minimum bactericidal concentration (MBC) of the essential oil from S. gracilis seeds were evaluated against eight Gram-positive bacteria (Listeria monocytogenes, Staphylococcus aureus, Staphylococcus epidermidis, Micrococcus luteus, Bacillus megaterium, Bacillus cereus, Bacillus coagulans and Bacillus subtilis), four Gram-negative bacteria (Salmonella enteritidis, Salmonella typhimurium, Klebsiella pneumoniae and Escherichia coli) and one fungus (Aspergillus niger). Results revealed that the essential oil from S. gracilis seeds exhibited significant in vitro antimicrobial property. Among all the tested microorganisms, the essential oil showed the strongest inhibitory effect against K. pneumoniae, whereas no inhibitory effect was found against L. monocytogenes and A. niger. Additionally, scanning electron microscopy (SEM) was used to observe morphological changes of bacteria treated with the essential oil from S. gracilis seeds. SEM observations confirmed the physical damage and considerable morphological alteration to the tested microorganisms treated with the essential oil. The data of this study suggests that the essential oil from S. gracilis seeds has great potential for application as a natural antimicrobial agent to preserve food.     

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.     

Growth of Escherichia coli and Staphylococcus aureus in individual lasagne layers and evidence for migration of E. coli throughout the product

Growth of Escherichia coli and Staphylococcus aureus within individual layers of lasagne was studied after spiking of ～10⁵–10⁶ CFU/g of each bacterial species into bolognese or béchamel sauces. Both E. coli and S. aureus grew by 3–4 log₁₀ cycles in each meal component. In a second study, alternate layers within a composite lasagne meal were spiked with ～10⁵–10⁶ CFU/g of E. coli and adjoining layers were monitored for possible bacterial migration. Spiked composite meals were subjected to either low temperature storage at 4 °C up to 8 h or to freeze chilling, which involved freezing at ?18 °C for 24 h followed by thawing at 4 °C up to 40 h. Migration of E. coli from inoculated layers to the adjoining layers was indicated by a recovery of substantial populations following both storage treatments. Migration appeared to be more limited for meals which underwent freeze chill treatment. In contrast, migration was evident throughout all product layers in meals stored at 4 °C only. Migration of bacteria throughout a multi-layered food may arise from differing compositional or structural characteristics within the product or from differing storage treatments. Therefore as a result of bacterial migration, it would appear that microbiological safety of multi-layered products such as lasagne relies on ensuring safety of each individual layer.     

Sanitization potency of slightly acidic electrolyzed water against pure cultures of Escherichia coli and Staphylococcus aureus,in comparison with that of other food sanitizers

The sanitization potency of slightly acidic electrolyzed water (SAEW) on pure cultures of Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli) was evaluated. The potency was compared with that of strong acidic electrolyzed water (StAEW) and sodium hypochlorite (NaOCl) solution. SAEW (ca. pH 5.8 and 21 mg/l available chlorine concentration; ACC) resulted into >5 log₁₀CFU/ml reduction of E. coli and S. aureus after 90 s of exposure. The relative bacterial reduction potency at each exposure time was in the order StAEW > NaOCl > SAEW and increased with exposure time, with relative effect being 90 s > 60 s > 30 s. The results indicate that SAEW with low ACC and near neutral pH can potentially sanitize E. coli and S. aureus within a short period of exposure presenting a potential replacement to NaOCl solution commonly used in the food industry.