Piezoelectric Flow Injection Analysis Biosensor for the Detection of Salmonella Typhimurium

ABSTRACT: Piezoelectric biosensors have the potential to provide direct detection of food contaminants, such as pathogens. In this study, Protein A antibody immobilization was used for the activation of the piezoelectric biosensor to detect Salmonella typhimurium. The overall system consisted of a new design for a flow cell and flow injection analysis system. The flow cell made possible a baseline stability of ± 1 Hz out of 5 MHz for hours. The sensor had responses of 5 to 65 Hz in 30 min with R²= 0.95 for S. typhimurium concentrations of 10⁷to 10⁹ CFU/ml under continuous flow, and 3 to 75 Hz in 40 min with R²= 0.96 for S. typhimurium concentrations of 10⁶ to 10¹⁰ CFU/ ml under stop flow. Cross-reactivity tests were performed with nonpathogenic Escherichia coli, Escherichia coli O157:H7, Listeria monocytogenes , and Vibrio parahaemolyticus and showed less than 10% response.     

IN VITRO COMPARISON OF ANAEROBIC AND AEROBIC GROWTH RESPONSE OF SALMONELLA TYPHIMURIUM TO ZINC ADDITION

Zinc supplemented diets have been used to provide zinc as a nutrient and higher concentrations have been used to induce molt in laying hens. It is not known if the zinc in these diets would inhibit Salmonella spp growth. This study examines the effects of zinc compounds on the growth of S. typhimurium poultry isolate under aerobic and anaerobic conditions. The aerobic growth response of S. typhimurium was determined either in tryptic soy broth (TSB) or minimal (M9) broth containing five different concentrations (0.67, 2.01, 3.35, 4.69, and 6.03% [wt/vol]) of either Zn acetate [Zn(C₂H₂O₂)₂2H₂O] or Zn sulfate [ZnSO₄7H₂O] while anaerobic growth response was determined in M9 broth with or without reductants (L-cysteine hydrochloride [C₃H₇NO₂SHCl], and sodium sulfide [Na₂S 9H₂O]). Aerobic growth rates inhibited (P < 0.05) by Zn acetate than by Zn sulfate in TSB medium. The Zn source and concentration decreased (P < 0.05) aerobic growth response of S. typhimurium poultry isolate in M9 medium. The growth rates of S. typhimurium under anaerobic growth conditions were less responsive to Zn salts but were generally lower (P < 0.05) in the presence of reductant than in the absence of reductants at each concentration of Zn compound. The results in this study provide evidence that Zn may inhibit S. typhimurium under in vitro aerobic or anaerobic atmospheric conditions and S. typhimurium grows less optimally under anaerobic growth conditions.     

LACTIC ACID INACTIVATION OF SALMONELLA TYPHIMURIUM ATTACHED TO CATFISH SKIN

This study was conducted to test sanitizer efficacy of lactic acid on Salmonella typhimurium populations that were firmly attached or loosely attached on catfish skin with or without mucus. For both cell types, counts of S. typhimurium were reduced from 5.9 log¹⁰ CFU/skin to below the limit of detection of 2.0 log¹⁰ CFU/skin by a 5 min exposure to 2% lactic acid. Exposure for 1 min reduced a 10⁴ CFU/skin inoculum to below the limit of detection. Catfish skin mucus slightly decreased the antimicrobial effect of lactic acid against firmly attached S. typhimurium.     

Short Chain Fatty Acids Alter HEp-2 Cell Association and Invasion by Stationary Growth Phase Salmonella Typhimurium

ABSTRACT: We examined the ability of stationary phase Salmonella typhimurium to adhere and invade cultured HEp-2 cells after growth in broth supplemented with acetate, propionate, butyrate, or a mixture of the three short chain fatty acids (SCFA). At pH 6, all concentrations, except 25 and 50 mM butyrate, reduced cell-association of S. typhimurium when compared to controls, while at pH 7 only 100 mM concentrations of acetate and butyrate reduced cell-association significantly. Invasion percentages were greater for S. typhimurium grown at an initial pH of 6 with 25 mM acetate when compared to controls, SCFA mixture, and all other single SCFA concentration combinations. At pH 7, invasion was greater with either the SCFA mixture or 25 or 50 mM acetate than with control and all other single SCFA concentration combinations.     

LATE LOGARITHMIC SALMONELLA TYPHIMURIUM HEp-2 CELL ASSOCIATION AND INVASION RESPONSE TO SHORT-CHAIN FATTY ACID ADDITION

The entry of Salmonella into the intestinal epithelial cells is essential for its pathogenesis. In the present stuay, late logarithmic growth (12 h) in Luria Bertani broth supplemented (25, 50, or 100 mM) with acetate, propionate, butyrate, or a mixture of the three short-chain fatty acids (SCFA), influenced the ability ofS. typhimurium to associate and invade cultured HEp-2 cells. The response to SCFA addition was dependent on the concentration and the pH of the medium. Cell-association was decreased 4 to 100-fold at pH 6 and 2 to 20-fold at pH 7. At pH 7, invasion was increased 2-fold when bacteria were cultured in the presence of all concentrations of acetate and 25 mM propionate or butyrate; however, a 1.5 to 163-fold decrease in invasion occurred at pH 6 for all SCFA. The SCFA concentration also affected cell-association and invasion of S. typhimurium, especially at pH 6. In general, for each of the SCFA at pH 6 a lower percentage of cell-association and invasion was observed as the SCFA concentration was increased while at pH 7 decreases did not consistently occur as SCFA concentration was increased. These differences among the SCFA along with the pH effects suggest that the concentration of SCFA and the pH of the intestinal lumen may influence the expression of the invasion phenotype of S. typhimurium.     

Combined Carbon Dioxide and High Pressure Inactivation of Pectin Methylesterase, Polyphenol Oxidase, Lactobacillus plantarum and Escherichia coli

ABSTRACT: High pressure processing (HPP) and CO₂have both been shown to increase food product shelf-life. CO₂ was added at approximately 0.2 molar % to solutions processed at 500 to 800 MPa in order to further inactivate pectin methylesterase (PME), polyphenol oxidase (PPO), L. plantarum ATCC 8014, and E. coli K12. An interaction was found between CO₂ and pressure at 25 °C and 50 °C for PME and PPO, respectively. Activity of PPO was decreased by CO₂ at all pressure treatments. The interaction between CO₂ and pressure was significant for L. plantarum with a significant decrease in survivors due to the addition of CO₂ at all pressures studied. No significant effect on E. coli survivors was seen with CO₂ addition.     

GROWTH RESPONSE OF A SALMONELLA TYPHIMURIUM POULTRY ISOLATE TO PROPIONIC ACID UNDER AEROBIC AND ANAEROBIC CONDITIONS

Organic acids have long been used as additives in poultry feed to reduce microbial populations, including Salmonella spp. Propionic acid addition to poultry feed has a potential role in reducing Salmonella spp. in the chicken intestine. In this study , in vitro growth response of S. typhimurium isolated from poultry to propionic acid under aerobic and anaerobic conditions was determined. When grown in tryptic soy broth (TSB) containing buffered propionic acid (BPA), the growth rate of S. typhimurium gradually decreased as the level of BPA increased and broth pH decreased. No growth was detected with BPA concentrations greater than 3% (volume/volume) of the broth. When the growth rates of S. typhimurium in aerobic and anaerobic TSB were compared at two pH levels (pH 5.0 and 7.0), the growth inhibition of S. typhimurium by propionic acid was markedly suppressed by anaerobiosis at both pHs, as indicated by significantly (p<0.05) higher half-inhibition constants (K°). Also, the growth rates of S. typhimurium in the presence of propionic acid were dramatically reduced by the decrease in pH from 7.0 to 5.0. The results of this study indicated that the growth inhibitory effect of propionic acid against S. typhimurium strains was enhanced by pH decrease and suppressed by anaerobiosis, suggesting that the growth response of S. typhimurium to propionic acid in the chicken intestine might be affected by the environmental conditions such as pH and anaerobiosis.     

Substantivity of sunscreens: an appraisal of some quaternary ammonium sunscreens

Two series of quaternary ammonium UV-B sunscreens, derived from salicylic acid (S) and from p -methoxycinnamic acid (C), and containing N-alkyl chains of different length (C₂ to C₁₆) were prepared and submitted to substantivity tests on animal (wool) keratin, and to microbiological tests. A direct correlation between substantivity and antimicrobial/antifungal activity was observed in all cases, the compounds bearing C₁₂ alkyl chains displaying peak values. The C-derivatives, when compared with the S-derivatives, showed relatively higher substantivity and sunscreen index (SI) values, coupled with lower antibacterial activity. The substantivity-microbiological activity correlations and the particular behaviour of the C₁₂ derivatives are briefly discussed in the light of the existing literature data. On the basis of the experimental results, possible guidelines for the development of substantive and non-antibacterial (and possibly, non-irritant) quaternary ammonium sunscreens are indicated.
La substantivité des filtres solaires     

HYGIENIZATION OF INDIAN CHICKEN MEAT BY IONIZING RADIATION

Both fresh and frozen chicken meat were evaluated for microbiological status by screening for total bacterial counts and for the presence of pathogens like Enterobacteria , Bacillus cereus, coagulase positive Staphylococci and Salmonella spp. Most of the samples exhibited heavy bacterial contamination (1.2 × 10⁵ - 2.6 × 10⁶/g), mainly with Staphylococcus spp. (1.5 × 10⁴ - 2.8 × 10⁵/g). All the chicken samples also showed the presence of Salmonellae (3 × 10¹ - 2.1 × 10²/g). Among the different serotypes observed in chickens . S. typhimurium was common in fresh as well as frozen chicken. Radicidation at 2 kGy at cryogenic conditions (−40°C) was efficient in eliminating the natural pathogenic contamination of the poultry . Salmonella spp. viz. S. seftenberg and S. typhimurium differed in radiation sensitivity, the D₁₀ values in phosphate buffer (pH 7.2) being 0.25 kGy and 0.12 kGy, respectively. Chicken homogenate (10%) offered approximately 2-fold protection to these cells. Chicken samples artificially inoculated with a heavy inoculum (10⁸ cells/g) of these 2 serotypes required higher gamma radiation doses of 4–5 kGy. The findings suggested that a dose of 2 kGy is adequate for normally contaminated chicken samples, but for the heavily contaminated chicken a dose of 4–5 kGy, depending upon the predominating Salmonella serotype present, is required .     

Lethal and Sublethal Action of Acetic Acid on Salmonella In Vitro and on Cut Surfaces of Apple Slices

ABSTRACT Antimicrobial action of acetic acid (AA) on Salmonella as affected by acid concentration, exposure time, culture age, and bacterial strains was investigated. Relative susceptibility of 6 Salmonella serovars to AA action was in the following order: S. bareilly > S. typhimurium > S. montevideo > S. poona > S. mbandaka > S. stanley. The stationary-phase cells of S. mbandaka were 100-fold more resistant to AA action than the log-phase cells. A mixture of Salmonella strains at a specified physiological stage should be used when testing the efficacy of the sanitizer treatment. Washing apple disks with NaOCl, H₂O₂, AA, or Na₃P0₄ greatly reduced the number of Salmonella and 30% to 40% of cells that survived were injured. Washing with a mixture of AA and H₂O₂ was the most effective in removing Salmonella from apple disks.     

EFFECT OF ELECTRICAL STIMULATION ON KILLING SALMONELLA TYPHIMURIUM IN VARIOUS SALT SOLUTIONS

Electrical stimulation was evaluated as a method to kill Salmonella typhimurium in various salt solutions at different concentration . Salmonella typhimurium at 2 × 10⁵ CFU/ml was treated at 22–24C for 60 min in each salt solution using electricity at 10 mA/cm² current, 1 kHz frequency, and 50% duty cycle. Samples taken at various times were serially diluted, plated on tryptic soy agar and xylose lysine desoxycholate agar, and incubated at 37C for 18–24 h. To detect injured cells, samples were also pre-enriched in buffered peptone water at 37C for 4–5h before being plated. Results indicated all salmonellae were electrically killed at 5 min in NaCl, at 30 min in NaNO₃, and at 45 min in NaC₂H₃O₂ at 0.15 and 0.015 M concentrations. Salmonellae were also killed at 45 min in Na₃PO₄ and at 60 min in Na₂CO₃ at 0.0015 M concentration by electricity in combination with high pH .     

DETECTION OF SALMONELLAE IN CHICKEN AND FISH SAMPLES USING DNA PROBE

The use of DNA probes for rapid identification of foodborne pathogens is an emerging field. We have standardized a method for the detection of Salmonella in food samples by using a specific insertion sequence (IS-200) of Salmonella chromosomal DNA as the probe. The procedure for colony hybridization, and washing conditions for the stringency were established. All the ten Salmonella strains, belonging to various serotypes tested were positive while 18 other bacterial cultures, mainly belonging to the family Enterobacteriaceae such as E. coli Shigella, Proteus etc., were negative in colony hybridization. The sensitivity of the detection was found to be 10⁵ cfu using ³²P-labeled probe. We surveyed 16 chicken and 6 fish samples from local market using IS-200 probe after preenrichment and selective enrichment. All the samples tested were found positive with DNA probe. The major strains of Salmonella isolated from these samples were S. gallinarum, S. typhimurium, S. enteritidis, S. choleraesuis and S. paratyphi A. These results were confirmed by standard Salmonella identification method.     

等离子体活化水对沙门氏菌的灭活作用及机制研究

等离子体活化水（Plasma-activated water,PAW）是一种新兴的非热杀菌技术,在食品保鲜等领域具有广泛的应用前景。本文研究了PAW处理对沙门氏菌（S. typhimurium）的杀灭效果及其作用机制。将经等离子体放电30、60和90 s得到的PAW分别记为PAW30、PAW60和PAW90。结果表明,PAW对S. typhimurium的杀菌效果随放电时间的延长而逐渐增强。当初始浓度为7.91 lg CFU/mL时,PAW60处理10 min后S. typhimurium活菌数减少了4.22 lg CFU/mL。扫描电镜（Scanning electron microscope,SEM）结果表明,PAW60处理后S. typhimurium细胞形态发生明显变化。经PAW60处理后,S. typhimurium胞外核酸和蛋白含量均显著（P<0.05）升高,表明其细胞膜通透性显著（P<0.05）增强。此外,PAW60处理破坏了S. typhimurium细胞外膜完整性,造成胞内活性氧水平显著（P<0.05）升高。以上实验结果表明,PAW处理能够有效灭活S. typhimurium,其作用机理可能与其破坏细胞结构、增强细胞膜通透性等有关。研究结果为PAW在食品杀菌保鲜中的应用提供了科学理论依据。     

EFFECTS OF TRISODIUM PHOSPHATE ON POPULATIONS OF SALMONELLA TYPHIMURIUM AND SALMONELLA ENTERITIDIS IN VITRO

This study determined the bactericidal activity of different concentrations of trisodium phosphate (TSP) against Salmonella typhimurium and Salmonella enteritidis in vitro. One milliliter of each TSP solution (0.5, 1, 1.5 and 2% w/v) was mixed with 1 mL of each bacterial culture and left to stand at room temperature (18  ±  1C) for 0, 15, 30, 45, 60 or 90 min before enumeration of the surviving pathogens.
The effects of 1.5 and 2% TSP were apparent on both bacterial species from 0 min and bacterial counts reached undetectable ( < 1.0  ×  10¹ cfu/mL) levels immediately. The 1% TSP solution effected close to 4.20–5.72 log reduction after 15 min. However, the reduction effect of 0.5% TSP was a function of treatment time, and some culturable bacteria remained even after 90 min of treatment. These results suggest that the bactericidal effect of TSP solution on these pathogens depends on its concentration and on the duration of treatment.

PRACTICAL APPLICATIONS

Poultry has been identified as one of the most important reservoirs of Salmonella typhimurium and Salmonella enteritidis in food chain. Efforts to eliminate or reduce Salmonella spp. and other pathogens attached to poultry carcasses during processing have been made for many years. In 1992, the U.S. Department of Agriculture approved the use of trisodium phosphate (TSP) as a processing aid to reduce Salmonella spp. on raw poultry carcasses. The aim of the present study was to determine the bactericidal effects of different concentrations of TSP on pure cultures of these pathogens in vitro .     

Use of Artificial Neural Network to Predict Temperature, Moisture, and Fat in Slab-Shaped Foods with Edible Coatings During Deep-Fat Frying

ABSTRACT: An artificial neural network (ANN) was developed to predict heat and mass transfer during deep-fat frying of infinite slab-shaped foods coated with edible films. Frying time, slab half-thickness, film thickness, food initial temperature, oil temperature, moisture diffusivity of food and film, fat diffusivity through food and film, thermal diffusivity of food, heat transfer coefficient, initial moisture content of food, and initial fat content of food (mf_o) were inputs. Temperature at the center (T₁), average temperature (T_ave), fat content (mf_ave), and moisture content (m_ave) of food were outputs. Four ANNs with 50 nodes each in 2 hidden layers with learning rate = 0.7 and momentum = 0.7 provided most accurate outputs, that is maximum absolute errors for T₁ and T_ave were < 1.2 °C, < 0.004 db for m_ave, and < 0.003 db for mf_ave. The predictions of mf varied linearly with mf.     

Sorbic acid diffusivity in relation to the composition of high and intermediate moisture model gels and foods

The diffusivity at infinite diffusant dilution ( D ₀) of sorbic acid in high and intermediate moisture gels (with various substrates and water contents) and in three foods was evaluated. The determination of D ₀(25°C) was achieved by tridimensional diffusion in gels cubes or by monodimensional diffusion in infinite food columns. For the same substrate concentration by weight, D₀ values of sorbic acid in concentrated sugar solutions decreased slightly when the molecular weight of the sugar was increased. When a liquid substrate such as glycerol was used, D ₀ values referred to equal concentrations by weight, were higher than in sugar solutions. The diffusion of sorbic acid is related, as a first approximation, to the water content rather than to the water activity of the diffusion medium.     

Selenium content in selected products of animal origin and estimation of the degree of cover daily Se requirement in Poland

The aim of the study was to determine Se concentration in selected products of animal origin (dairy products, pork, beef, chicken, giblets, fish, eggs) and to estimate the degree to which these products cover daily Se requirement in humans. Selenium concentrations were determined using the spectrofluorometric method. Mean Se concentration in the milk, yoghurt, kefir, and probiotic drinks was 0.020 μg mL⁻¹, 0.010 μg mL⁻¹, 0.012 μg mL⁻¹ and 0.012 μg mL⁻¹, respectively. Selenium concentration in cheese ranged 0.022–0.088 μg g⁻¹ wet weight. The average selenium content of meat ranged from 0.064 (beef) to 0.094 (chicken) μg g⁻¹ w.w. The mean Se content of giblets (liver: 0.307–0.401 μg g⁻¹ w.w.) was significantly ( P  < 0.05) higher than in meat. The concentration of Se depends on fish species and in our study it ranged from 0.136 ± 0.023 (flounder) to 0.282 ± 0.024 μg g⁻¹ w.w. (mackerel). The results obtained show that the analysed food provides 22.8% of the daily selenium requirement. Considering that animal products account for 40–45% of the diet daily selenium intake averages 33–37 μg.     

Reaction of melanoidins with sulphur dioxide: stoichiometry of the reaction

Sulphur dioxide, in the form of sulphur(IV) oxoanions(S(IV)), e.g. HSO^-₃, SO^2-₃, reacts irreversibly with non-enzymic browning model melanoidins (M_r > 12000, prepared by combination of 1.25 mol glucose with 1 mol glycine (pH 5.5, 90°C, 22 hr)). When the reaction with S(IV) is carried out for > 39 days at 40°C and pH 5.5 with initial concentrations of melanoidin of 5.71 g/l and S(IV) of 0.0371 M (equivalent to c . 2400 ppm SO₂), up to one sulphur atom is incorporated for every two molecules of glucose used to form the polymer. This stoichiometry is discussed in relation to the degree of unsaturation of the melanoidin.     

The Acetic Acid Tolerance Response induces cross-protection to salt stress in Salmonella typhimurium

Salmonella typhimurium induces an Acid Tolerance Response (ATR) upon exposure to mildly acidic conditions in order to protect itself against severe acid shock. This response can also induce cross-protection to other stresses such as heat and salt. We investigated whether both the acetic acid induced and lactic acid induced ATR in S. typhimurium provided cross-protection to a salt stress at 20 degrees C. Acid-adapted cells were challenged with both a sodium chloride (NaCl) and potassium chloride (KCl) shock and their ability to survive ascertained. Acetic acid adaptation provided cells with protection against both NaCl and KCl stress. However, lactic acid adaptation did not protect against either osmotic stressor and rendered cells hypersensitive to NaCl. These results have implications for the food industry where hurdle technology means multiple sub-lethal stresses such as mild pH and low salt are commonly used in the preservation of products.