Efficacy of disinfectant and bacteriophage mixture against planktonic and biofilm state of Listeria monocytogenes to control in the food industry

Fresh produce and animal-based products contaminated with Listeria monocytogenes have been the main cause of listeriosis outbreaks for many years. The present investigation explored the potential of combination treatment of disinfectants with a bacteriophage cocktail to control L. monocytogenes contamination in the food industry. A mixture of 1 minimal inhibitory concentration (MIC) of disinfectants (sodium hypochlorite [NaOCl], hydrogen peroxide [H2O2], and lactic acid [LA]) and multiplicity of infection (MOI) 100 of phage cocktail was applied to both planktonic cells in vitro and already-formed biofilm cells on food contact materials (FCMs; polyethylene, polypropylene, and stainless steel) and foods (celery and chicken meat). All the combinations significantly lowered the population, biofilm-forming ability, and the expression of flaA, motB, hlyA, prfA, actA, and sigB genes of L. monocytogenes. Additionally, in the antibiofilm test, approximately 4 log CFU/cm2 was eradicated by 6 h treatment on FCMs, and 3 log CFU/g was eradicated within 3 days on celery. However, <2 log CFU/g was eradicated in chicken meat, and regrowth of L. monocytogenes was observed on foods after 5 days. The biofilm eradication efficacy of the combination treatment was proven through visualization using scanning electron microscopy (SEM) and confocal microscopy. In the SEM images, the unusual behavior of L. monocytogenes invading from the surface to the inside was observed after treating celery with NaOCl+P or H2O2 + P. These results suggested that combination of disinfectants (NaOCl, H2O2, and LA) with Listeria-specific phage cocktail can be employed in the food industry as a novel antimicrobial and antibiofilm approach, and further research of L. monocytogenes behavior after disinfection is needed.

Control of Listeria monocytogenes in food industry by a combination treatment of natural aromatic compound with Listeria-specific bacteriophage cocktail

Most Listeria monocytogenes found in the food industry are listeriosis-causing pathogens and possess the ability to form biofilms on food and food contact materials (FCMs). This study aims to evaluate the efficacy of the combination treatment of natural aromatic compounds (thymol, eugenol, carvacrol, and citral) with a Listeria-specific phage cocktail in mitigating the threat posed by L. monocytogenes in the food industry. In vitro combination treatment of 1 minimal inhibitory concentration (MIC) of natural aromatic compound with phage cocktail at multiplicity of infection (MOI) 100 reduced more than 4 log CFU/mL of L. monocytogenes planktonic cells and inhibited biofilm formation. In addition, the expression of virulence-related genes (flaA, motB, hlyA, prfA, and actA) and the stress response (sigB) gene were significantly downregulated. The combination of natural aromatic compound with phage cocktail reduced the biofilm cell population on contaminated celery by more than 2 log CFU/g and by more than 2 log CFU/cm2 on already-formed biofilm on FCMs, but it was less effective on chicken meat, with an approximate reduction of only 1 log CFU/g. The antibiofilm activity toward preformed L. monocytogenes biofilms was also observed using field-emission scanning electron microscopy (FESEM) and confocal laser scanning microscopy (CLSM). COMSTAT analysis of the structural change of biofilms revealed that major biofilm structure parameters (biovolume, thickness, diffusion distance, and microcolonies at substratum) were reduced after treatment. Our findings suggest that the combination of natural aromatic compounds with a phage cocktail has enormous potential as an antimicrobial and antibiofilm agent for controlling L. monocytogenes in the food industry.

Effect of sublethal concentrations of bactericidal antibiotics on mutation frequency and stress response of Listeria monocytogenes

The purpose of this study was to investigate sublethal concentrations (SLC) of bactericidal antibiotics (ampicillin, gentamicin, kanamycin, and vancomycin) on the mutation frequency and stress response of antibiotic-induced-mutated (AIM) Listeria monocytogenes. Three L. monocytogenes strains (reference, clinical, and food isolate strains) were used in this study. SLC of bactericidal antibiotics significantly increased the mutation frequency in L. monocytogenes. It was found that AIM L. monocytogenes had a superior biofilm-forming ability than nontreated L. monocytogenes. This result correlated with the amounts of EPS produced (polysaccharide and protein) in the early stage of biofilm formation. AIM L. monocytogenes showed strong viability under food-associated stress (thermal, osmotic, and acidic) compared to nontreated L. monocytogenes. In addition, expression levels of motility (flaA) and virulence genes (hlyA, actA, and prfA) of AIM L. monocytogenes were significantly downregulated in the reference strain but significantly upregulated or similar to the expression levels in the clinical and food isolate strains compared to nontreated L. monocytogenes. Based on our results, SLC of bactericidal antibiotics increased the mutation frequency in L. monocytogenes, facilitated the adaptation of the bacterium to food-associated stress, and led to an increase in its pathogenicity.

Combination treatment of peroxyacetic acid or lactic acid with UV-C to control Salmonella Enteritidis biofilms on food contact surface and chicken skin

The risk of salmonellosis is expected to increase with the rise in the consumption of poultry meat. The aim of this study was to investigate the combination treatment of peroxyacetic acid (PAA) or lactic acid (LA) with UV-C against Salmonella Enteritidis biofilms formed on food contact surface (stainless steel [SS], silicone rubber [SR], and ultra-high molecular weight polyethylene [UHMWPE]) and chicken skin. The biofilm on food contact surface and chicken skin was significantly decreased (P < 0.05) by combination treatment of PAA or LA with UV-C. Combination treatment of PAA (50-500 μg/mL) with UV-C (5 and 10 min) reduced 3.10-6.41 log CFU/cm² and LA (0.5-2.0%) with UV-C (5 and 10 min) reduced 3.35-6.41 log CFU/cm² of S. Enteritidis biofilms on food contact surface. Salmonella Enteritidis biofilms on chicken skin was reduced around 2 log CFU/g with minor quality changes in color and texture by combination treatment of PAA (500 μg/mL) or LA (2.0%) with UV-C (10 min). Additional reduction occurred on SS and UHMWPE by PAA or LA with UV-C, while only LA with UV-C caused additional reduction on chicken skin. Also, it was visualized that the biofilm on food contact surface and chicken skin was removed through field emission scanning electron microscopy (FESEM) and death of cells constituting the biofilm was confirmed through confocal laser scanning microscopy (CLSM). These results indicating that the combination treatment of PAA or LA with UV-C could be used for S. Enteritidis biofilm control strategy in poultry industry.

First Observation of Ferroelectricity in ∼1 nm Ultrathin Semiconducting BaTiO3 Films

The requirements of multifunctionality in thin-film systems have led to the discovery of unique physical properties and degrees of freedom, which exist only in film forms. With progress in growth techniques, one can decrease the film thickness to the scale of a few nanometers (∼nm), where its unique physical properties are still pronounced. Among advanced ultrathin film systems, ferroelectrics have generated tremendous interest. As a prototype ferroelectric, the electrical properties of BaTiO₃ (BTO) films have been extensively studied, and it has been theoretically predicted that ferroelectricity sustains down to ∼nm thick films. However, efforts toward determining the minimum thickness for ferroelectric films have been hindered by practical issues surrounding large leakage currents. In this study, we used ∼nm thick BTO films, exhibiting semiconducting characteristics, grown on a LaAlO₃/SrTiO₃ (LAO/STO) heterostructure. In particular, we utilized two-dimensional electron gas at the LAO/STO heterointerface as the bottom electrode in these capacitor junctions. We demonstrate that the BTO film exhibits ferroelectricity at room temperature, even when it is only ∼2 unit-cells thick, and the total thickness of the capacitor junction can be reduced to less than ∼4 nm. Observation of ferroelectricity in ultrathin semiconducting films and the resulting shrunken capacitor thickness will expand the applicability of ferroelectrics in the next generation of functional devices.

Simultaneous organic and nitrogen removal from municipal landfill leachate using an anaerobic-aerobic system

An anaerobic-aerobic system including simultaneous methanogenesis and denitrification was introduced to treat organic and nitrogen compounds in immature leachate from a landfill site. Denitrification and methanogenesis were successfully carried out in the anaerobic reactor while the organic removal and nitrification of NH4+,-N were carried out in the aerobic reactor when rich organic substrate was supplied with appropriate hydraulic retention time. The maximum organic removal rate was 15.2 kg COD/m3 d in the anaerobic reactor while the maximum NH4+-N removal rate and maximum nitrification rate were 0.84kg NH4+-N/m3/d and 0.50kg NO3--N/m3/d, respectively, in the aerobic reactor. The pH range for proper nitrification was 6-8.8 in the aerobic reactor. The organic compounds inhibited nitrification so that the organic removal in the anaerobic reactor could enhance the nitrification rate in the following aerobic reactor. The gas production rate was 0.33 m3/kg COD and the biogas compositions of CH4, CO2, and N2 were kept relatively constant, 66-75, 22-32, and 2-3%, respectively.

The menopausal transition: change, loss, and adaptation

The menopausal transition may be regarded as a developmental stage in the life cycle during which women gradually adapt to biologic, social, psychologic, and spiritual changes that accompany ovarian decline and menstrual cessation. Although the biomedical view stresses atrophic and degenerative changes, a developmental and holistic perspective stresses the individuality, totality, and complexity of responses to this experience. Sensitive care during the menopausal transition may enable women to accept the inevitable changes and losses and recognize qualities and capabilities that can unfold. The author is a nurse specialist in women's health care who draws from her research and clinical practice to provide illustrations for her perspective.

Activation of phospholipase D by guanosine 5'[gamma-thio]triphosphate and AlF4- in bovine corneal epithelial cells

We have investigated the regulation of phospholipase D (PLD) by guanine nucleotides and AlF4- in bovine corneal epithelial cells (BCEC) prelabeled with [3H]myristic acid. In the presence of ethanol, AlF4- increased the production of [3H]PA and [3H]PET indicating activation of PLD in these cells. The effects of AlF4- were time- and dose-dependent. Addition of guanosine 5[gamma-thio]triphosphate (GTP gamma S), to streptolysin O-permeabilized cells also resulted in increased accumulation of [3H]PA and [3H]PEt. Other guanine and adenine nucleotides were ineffective, and guanosine thiodiphosphate inhibited the GTP gamma S-induced activation of PLD. Direct addition of GTP gamma S to microsomal fraction prepared from [3H]myristate-labeled BCEC resulted in increased formation of [3H]PEt in a time- and dose-dependent manner. The activation of PLD by GTP gamma S in the microsomal fraction was absolutely dependent on the presence of Ca2+ > 0.5 microM. Addition of Ca2+ (10-100 microM) alone dose-dependently stimulated the PLD activity. Treatment of the microsomal fraction with phorbol esters had no effect on the ability of GTP gamma S to stimulate PLD. Addition of isoproterenol to BCEC resulted in several-fold stimulation of cAMP, but it had no effect on basal or PDBu-induced stimulation of PLD. Taken together, the data suggest that a GTP-binding protein is involved in regulation of PLD in BCEC, and that maximal stimulation of PLD probably results from an interaction between Ca2+, PKC and G-protein in BCEC.

Stimulation of phospholipase D by phorbol esters and ionomycin in bovine corneal epithelial cells

This study was performed to determine the effects of phorbol esters and ionomycin on phospholipase D (PLD) activity in bovine corneal epithelial cells (BCEC). The cells were prelabeled with [3H]myristic acid and incubated for specific time intervals with various test agents in the presence and absence of ethanol. The PLD activity was assayed by monitoring the formation of labeled phosphatidylethanol ([3H]PEt) in [3H]myristate labeled cells. In the absence of ethanol, 1 microM phorbol 12-myristate 13-acetate (PMA) increased the formation of labeled phosphatidic acid ([3H]PA) with no significant effect on the radioactivity of [3H]PEt. In the presence of 85 mM ethanol, whereas there was only a small further increase in [3H]PA, the formation of [3H]PEt was increased by several-fold, demonstrating activation of PLD by the phorbol ester. The effects of PMA were time- and dose-dependent, and were mimicked by phorbol 12,13-dibutyrate. The inactive phorbol derivatives, 4-alpha-phorbol, 4-alpha-phorbol 12,13-didecanoate, 4-alpha-phorbol 12-myristate 13-acetate and 4-alpha-phorbol 12,13-dibutyrate, were without effect. Short-time (30 min) incubation of BCEC with staurosporine or H-7, or prolonged (20 hours) incubation with PMA rendered the cells less sensitive to subsequent treatment with PMA, suggesting that activation of PLD in the cells is mediated by protein kinase C (PKC). Addition of 20 microM ionomycin in the presence of ethanol also increased the formation of [3H]PA and [3H]PEt in a time- and dose-dependent manner. Co-presence of ionomycin and PMA at submaximal concentrations in the incubation medium resulted in increased formation of [3H]PA and [3H]PEt which was less than their individual effects combined, indicating a lack of synergism between Ca2+ and PMA in activating PLD. Incubation of BCEC with staurosporine resulted in significant inhibition of ionomycin-induced production of [3H]PEt, suggesting that in addition to direct activation of PLD by Ca2+, the enzyme is probably stimulated by sequential activation of PLC (producing diacylglycerol) and PKC following the ionomycin addition. We conclude that BCEC possess PLD which is stimulated by PKC as well as elevated intracellular Ca2+.