Survival of Escherichia coli O157:H7 in soil and on carrots and onions grown in fields treated with contaminated manure composts or irrigation water

Many foodborne outbreaks of enterohemorrhagic Escherichia coli O157:H7 infection have been associated with the consumption of contaminated vegetables. On-farm contaminations through contaminated manure or irrigation water application were considered likely sources of the pathogen for several outbreaks. Field studies were done to determine the survival of E. coli O157:H7 on two subterranean crops (carrots and onions), and in soil fertilized with contaminated manure compost or irrigated with contaminated water. Three different types of composts, PM-5 (poultry manure compost), 338 (dairy manure compost) and NVIRO-4 (alkaline stabilized dairy manure compost), and irrigation water were inoculated with an avirulent strain of E. coli O157:H7 at 10⁷ cfu g⁻¹ and 10⁵ cfu ml⁻¹, respectively. A split-plot block design plan was used for each crop, with five treatments (one without compost, three with each of the three composts, and one without compost but with contaminated irrigation water applied) and five replicates for a total of 25 plots, each measuring 1.8×4.6 m², for each crop. Composts were applied to soil as a strip at a rate of 4.5 metric tons ha⁻¹ before carrots and onions were sown. Contaminated irrigation water was sprayed once on the vegetables at the rate of 2 l per plot for this treatment 3 weeks after carrots and onions were sown. E. coli O157:H7 survived in soil samples for 154–196 days, and was detected for 74 and 168 days on onions and carrots, respectively. E. coli O157:H7 survival was greatest in soil amended with poultry compost and least in soil containing alkaline-stabilized dairy manure compost. Survival profiles of E. coli O157:H7 on vegetables and soil samples, contaminated either by application of contaminated compost or irrigation water, were similar. Hence, preharvest contamination of carrots and onions with E. coli O157:H7 for several months can occur through both contaminated manure compost and irrigation water.     

The growth and survival of Escherichia coli O157:H7 on minced bison and pieces of bison meat stored at 5 and 10 °C

This study investigated the growth and survival of Escherichia coli O157:H7 on minced and whole pieces of bison meat. Growth curves of native microflora, including Pseudomonas spp. and Enterobacteriaceae were also generated. A marked E. coli O157:H7 strain was inoculated onto minced and whole pieces of bison meat at an initial level of 1.5 log₁₀ cfu g⁻¹. The inoculated meat was stored at either 5 °C for 28 days or 10 °C for 21 days. Survival, but no growth, of E. coli O157:H7 was observed on both forms of bison meat stored at 5 °C, while significant growth of the organism was observed at 10 °C. E. coli O157:H7 counts on whole pieces were generally higher than counts observed on minced bison meat, and reached their highest population by 14 days, with a total increase of 3.36 log₁₀ cfu g⁻¹ on whole pieces and 2.12 log₁₀ cfu g⁻¹on minced bison meat stored at 10 °C. Under the same storage temperature, Pseudomonas spp. and total counts displayed similar growth patterns on both pieces and minced bison meat, while the Enterobacteriaceae showed a slower growth rate. This study showed that the growth of E. coli O157:H7 on bison meat is similar to that observed in studies of beef.     

An immuno-capturing and concentrating procedure forEscherichia coliO157:H7 and its detection by epifluorescence microscopy

Escherichia coliO157:H7 cells were captured on a polyvinyl chloride (PVC) sheet coated with polyclonal anti-E. coli O157:H7 antibody, and stained with fluorescein-labelled anti-E. coliO157:H7 antibody. The cells were then scraped off the PVC surface in water, concentrated by filtering through a 3-mm diameter area of polycarbonate membrane filter, and counted by epifluorescence microscopy. This procedure was specific forE. coliO157:H7, highly sensitive, allowing detection ofE. coli0157:H7 at 4.7×10¹–1.3×10²cfu ml⁻¹, and required less than 2 h to execute. The presence of animal tissue fluids (i.e., beef liver and chicken exudates) or cow faeces did not inhibit the capturing of bacterial cells by the antibody-coated PVC. Although beef liver exudate interfered with filtration and slightly reduced the number of cells detected, treatment with trypsin improved the filterability but did not improve detection sensitivity.     

Enterobacteriaceae in beef products from retail outlets in the Republic of Ireland and comparison of the presence and counts of E. coli O157:H7 in these products

This study investigated the prevalence and numbers of Enterobacteriaceae in minced beef and beef burgers purchased from supermarkets and butcher shops in the Republic of Ireland (RoI). Samples (n=1303) collected between June 2001 and April 2002 from every county in the RoI (∼60 per county) were examined for the presence of Enterobacteriaceae using method BS 5763. Overall, in the 43 beef products in which E. coli O157:H7 was present the Enterobacteriaceae counts ranged from 0.52 to 6.98 log₁₀ cfu g⁻¹. There was no correlation between the number of Enterobacteriaceae and the presence of E. coli O157:H7. There were no significant differences between Enterobacteriaceae numbers in fresh, unpackaged, minced beef samples from butcher shops and supermarkets, or in fresh, unpackaged, beef burgers from butcher shops and supermarkets. However, there were significant differences among the numbers of Enterobacteriaceae detected in different minced beef products. The numbers of Enterobacteriaceae in fresh, unpackaged, minced beef (6.54–6.98 log₁₀ cfu g⁻¹) were considerably higher than in preprepared or prepackaged minced beef (2.95–3.62 log₁₀ cfu g⁻¹).     

Monitoring of Escherichia coli O157:H7 in food samples using lectin based surface plasmon resonance biosensor

A novel surface plasmon resonance (SPR) biosensor using lectin as bioreceptor was developed for the rapid detection of Escherichia coli (E. coli) O157:H7. The selective interaction of lectins with carbohydrate components from bacterial cells surface was used as the recognition principle for the detection. Five types of lectins from Triticum vulgaris, Canavailia ensiformis, Ulex europaeus, Arachis hypogaea, and Maackia amurensis, were employed to evaluate the selectivity of the approach for binding E. coli O157:H7 effectively. A detection limit of 3 × 10³ cfu mL^?1 was obtained for determination of E. coli O157:H7 when used the lectin from T. vulgaris as the binding molecule. Furthermore, the proposed biosensor was used to detect E. coli O157:H7 in real food samples. Results showed that the lectin based SPR biosensor was sensitive, reliable and effective for detection of E. coli O157:H7, which hold a great promise in food safety analysis.     

Hard surfaces decontamination of enteropathogenic and Shiga toxin-producing Escherichia coli using bacteriophages

Three Myoviridae phages (DT1, DT5 and DT6) specific for pathogenic Escherichia coli were studied, either individually or as cocktails, for their lytic activity on in vitro challenge tests. Also, cocktail ability to reduce artificial contamination on hard surfaces (glass coverslips and stainless steel coupons) by three pathogenic Escherichia coli strains (EPEC920, non-O157 STEC ARG4827 and O157:H7 STEC464) was tested. Assays of phage stability during refrigerated storage showed that the three phages evaluated retained a high viability after two months at 4 °C. Challenge tests showed high reductions in viable cells, of up to 6.4 log CFU ml^− 1, for all tested strains at 37 °C. Efficiency was somewhat lower at 4 °C, though biocontrol levels were still good, reaching values of up to 3.8 log CFU ml^− 1. Considering only results obtained at 37 °C, phage cocktails produced the highest reduction in most cases. Treatments with phage cocktails produced complete inactivation (ca. 5–6 log CFU ml^− 1) of EPEC920 and O157:H7 STEC464 on glass coverslips, and of EPEC920, non-O157 STEC ARG4827 and O157:H7 STEC464 on stainless steel coupons, at both temperatures (4 °C and 37 °C) and multiplicity of infection (ca. 10³ and 10⁷) tested. However, some strains not detected at 3 h were sometimes detected at 24 h, and inactivation of non-O157 STEC ARG4827 on glass coverslips was never accomplished; viable cell reductions in all these cases ranged from 1.2 to 5.4 log CFU ml^− 1. Our results suggest that lytic phages, either individually or as a cocktail, may be useful for reducing contamination on hard materials used in food processing surfaces. To our knowledge, this is the first study focused on the use of bacteriophages to reduce contamination of food processing surfaces by EPEC and non-O157 STEC strains.     

The influence of lactoperoxidase,heat and low pH on survival of acid-adapted and non-adapted Escherichia coli O157:H7 in goat milk

In hot climates where quality of milk is difficult to control, a lactoperoxidase (LP) system can be applied in combination with conventional preservation treatments at sub-lethal levels to inhibit pathogenic microbes. This study investigated the effect of combined heat treatments (55 °C, 60 °C and 72 °C) and milk acidification (pH 5.0) on survival of acid-adapted and non-adapted Escherichia coli O157:H7 strains UP10 and 1062 in activated LP goat milk. Heat treatment at 72 °C eliminated E. coli O157:H7. Acid-adapted strains UP10 and 1062 cells showed resistance to combined LP and heat at 60 °C in fresh milk. The inhibition of acid-adapted and non-adapted E. coli O157:H7 in milk following combined LP-activation, heat (60 °C) and milk acidification (pH 5.0) suggests that these treatments can be applied to reduce E. coli O157:H7 cells in milk when they occur at low numbers (<5 log₁₀ cfu mL^?1) but does not eliminate E. coli O157:H7 to produce a safe product.     

Microbiological conditions of moisture-enhanced pork before and after cooking

Substantial numbers of aerobic bacteria but few coliforms or Listeria spp. and no Escherichia coli were recovered from both swab samples and brines circulated in cleaned equipment used for injecting pork loins. After meat was processed for 30 or 60 min, the numbers of aerobic bacteria in brines had increased by >1 log unit, to about 4.5 log cfu ml⁻¹, but coliforms were <2 and E. coli and Listeria spp. were <1 log cfu ml⁻¹. The numbers of bacteria on the surfaces of pork loins before and after injection of the meat were similar. No bacteria were recovered from the deep tissues of the uninjected meat, but aerobic bacteria were recovered at log-mean numbers of 2.1 log cfu g⁻¹ and coliforms at log-total numbers of 1.2 log cfu 25 g⁻¹ from 25 samples of deep tissues of injected meat. Aerobic bacteria were recovered at log total numbers of 1.0 log cfu 25 g⁻¹ from 25 samples of injected pork cooked to a central temperature of 61 °C, but no bacteria were recovered from the deep tissues of meat cooked to 70 °C. The findings suggest that moisture-enhanced pork cooked to a medium rare condition can be microbiologically safe.     

Influence of pH and NaCl on monolaurin inactivation of Streptococcus iniae

Streptococcus iniae, a Gram-positive bacterium, has been recognized as a cause of human and fish streptococcosis. Aquacultured fish are susceptible to infection and have been epidemiologically linked with wound infections of fish handlers. Therefore, there is a need to develop methods of prevention and/or control of this pathogen. This study determined the minimum inhibitory concentration of monolaurin (glycerol monolaurate) against S. iniae strains PW and BU and utilized gradient plates at 37°C to determine the combined influence of pH and NaCl on monolaurin inactivation of S. iniae. The minimum inhibitory concentration of monolaurin against strain PW was 12.4±0.3 μg ml⁻¹ and against strain BU was 12.1±0 μg ml⁻¹. Compared to growth in the absence of monolaurin, the incorporation of 6 μg ml⁻¹ monolaurin into the salt (1.12–6.95%)–pH (4.26–8.88) gradient plates prevented growth of strain PW at pH values <6.00 and strain BU at pH values <6.20, regardless of the salt concentration. The combination of monolaurin with environmental variables such as pH and salt proved to be an effective tool for in vitro control of S. iniae.     

Antimicrobial activity of pediocin-producing Lactococcus lactis on Listeria monocytogenes,Staphylococcus aureus and Escherichia coli O157:H7 in cheese

The antimicrobial activity of two pediocin-producing transformants obtained from wild strains of Lactococcus lactis on the survival of Listeria monocytogenes, Staphylococcus aureus and Escherichia coli O157:H7 during cheese ripening was investigated. Cheeses were manufactured from milk inoculated with the three pathogens, each at approximately 6 log cfu mL⁻¹. Pediococcus acidilactici 347 (Ped⁺), Lc. lactis ESI 153, Lc. lactis ESI 515 (Nis⁺) and their respective pediocin-producing transformants Lc. lactis CL1 (Ped⁺) and Lc. lactis CL2 (Nis⁺, Ped⁺) were added at 1% as adjuncts to the starter culture. After 30 d, L. monocytogenes, S. aureus and E. coli O157:H7 counts were 5.30, 5.16 and 4.14 log cfu g⁻¹ in control cheese made without adjunct culture. On day 30, pediocin-producing derivatives Lc. lactis CL1 and Lc. lactis CL2 lowered L. monocytogenes counts by 2.97 and 1.64 log units, S. aureus by 0.98 and 0.40 log units, and E. coli O157:H7 by 0.84 and 1.69 log units with respect to control cheese. All cheeses made with nisin-producing LAB exhibited bacteriocin activity throughout ripening. Pediocin activity was only detected throughout the whole ripening period in cheese with Lc. lactis CL1. Because of the antimicrobial activity of pediocin PA-1, its production in situ by strains of LAB growing efficiently in milk would extend the application of this bacteriocin in cheese manufacture.     

Inactivation of Escherichia coli O157:H7 and Listeria monocytogenes in milk by caprylic acid and monocaprylin

Listeria monocytogenes and Escherichia coli O157:H7 are major foodborne pathogens implicated in various outbreaks involving pasteurized or unpasteurized milk, and various dairy products. The objective of this study was to determine the antibacterial effect of caprylic acid (CA, C_8:0) and its monoglyceride, monocaprylin (MC) on L. monocytogenes and E. coli O157:H7 in whole milk. A five-strain mixture of E. coli O157:H7 or L. monocytogenes was inoculated in autoclaved milk (10⁶ CFU/ml) containing 0, 25, or 50 mM of CA or MC. At 37°C, all the treatments, excepting 25 mm CA, reduced the population of both pathogens by approximately 5.0 log CFU/ml in 6 h. At 24 h of storage at 8°C, MC at both levels and CA at 50 mM decreased L. monocytogenes and E. coli O157:H7, respectively by >5.0 log CFU/ml. At 48 h of 4°C storage, populations of L. monocytogenes and E. coli O157:H7 were decreased to below detection level (enrichment negative) by 50 mm of MC and CA, respectively. Results indicate that MC could potentially be used to inhibit L. monocytogenes and E. coli O157:H7 in milk and dairy products, but sensory studies need to be conducted before recommending their use.     

In-vitro mineral binding capacity of five fiber sources and their insoluble components for magnesium and calcium1

In-vitro binding of calcium (Ca) and magnesium (Mg) by total dietary fiber, hemicellulose A (HCL A), lignocellulose (LCL), cellulose (CL), and lignin (L) fractions isolated from rice bran (RB), wheat bran (WB), oat fiber (OF), apple fiber (AF) and tomato fiber (TF) was evaluated. At pH 6.8, significant amounts of Ca were bound by whole fibers, ranging from 800 μg g⁻¹ for RB to 10 097 μg g⁻¹ for TF. Mg bound by whole fibers varied from 496 μg g⁻¹ for OF to 2177 μg g⁻¹ for WB. Re-acid washing (pH<2.0) released 95–99% of the Ca and Mg bound to the fibers. Fibers with the highest endogenous Ca and Mg concentrations bound significantly (P<0.05) the highest amounts of the minerals studied. The Ca bound by HCL A varied from 9753 μg g⁻¹ for RB to 11 337 mg g⁻¹ for TF, whereas Mg bound varied from 1151 μg g⁻¹ for OF to 5626  μg g⁻¹ for TF hemicellulose fractions, respectively. Among the fiber components, Mg binding decreased in the order HCL A>LCL>L>CL, whereas Ca bound was in the order HCL A>LCL>CL>L. A relatively strong correlation was observed between the combined effects of protein content, hemicellulose, and lignin vs total Ca and Mg bound. 1998 Elsevier Science Ltd. All rights reserved     

Antimicrobial agent detection in ewes’ milk by the microbial inhibitor test brilliant black reduction test—BRT AiM®

The detection limits of 24 antimicrobial agents were determined in ewes’ milk by one commercially available version of brilliant black reduction test, BRT Inhibitor Test with prediffusion AiM^® (BRT AiM^®). For each drug, eight concentrations were tested on 20 milk samples from individual ewes. The detection limits of the BRT AIM^® method were determined by means of logistic regression models: 6 μg kg⁻¹ amoxycillin, 6 μg kg⁻¹ ampicillin, 51 μg kg⁻¹ cloxacillin, 2 μg kg⁻¹ penicillin “G”, 230 μg kg⁻¹ cefadroxil, 1330 μg kg⁻¹ cephalosporin “C”; 270 μg kg⁻¹ cephalexin, 92 μg kg⁻¹ cefoperazone, 120 μg kg⁻¹ ceftiofur, 69 μg kg⁻¹ cefuroxime, 6000 μg kg⁻¹ streptomycin, 1200 μg kg⁻¹ gentamycin, 3700 μg kg⁻¹ neomycin, 630 μg kg⁻¹ erythromycin, 120 μg kg⁻¹ tylosin, 390 μg kg⁻¹ doxycycline, 5500 μg kg⁻¹ oxytetracycline, 6200 μg kg⁻¹ tetracycline, 5400 μg kg⁻¹ sulfadiazine, 3200 μg kg⁻¹ sulfamethoxazole, 6500 μg kg⁻¹ sulfamethoxypyridazine, 6200 μg kg⁻¹ sulfaquinoxaline, 22000 μg kg⁻¹ chloramphenicol and 4100 μg kg⁻¹ trimethoprim. The BRT AiM^® method presents detection limits for β-lactam antibiotics that are similar to those obtained as Maximum Residue Limits (MRLs) according to Regulation 2377/90 EEC as set out by the European Union. However, for other antimicrobial agents the estimated limits were higher than those of the EU-MRLs. It is therefore advisable to enhance the sensitivity of the method for the detection of the different antimicrobial groups or to develop a combined system of different microbiological inhibitor tests that would enable the detection of a greater number of antimicrobial agents.     

Isolation and characterisation of a novel antibacterial peptide from bovine αS1-casein

Bovine casein was hydrolysed with a range of proteolytic enzymes including pepsin, trypsin, α-chymotrypsin and β-chymotrypsin, and assessed for antibacterial activity. The pepsin digest of bovine casein, which showed antibacterial activity, was fractionated using reverse phase high performance liquid chromatography and the antibacterial peptides isolated were characterised using electrospray ionisation mass spectrometry. Two antibacterial peptides were identified, a novel peptide (Cp1) which corresponded to residues 99–109 of bovine α_S1-casein and a previously reported peptide (Cp2) which corresponded to residues 183–207 of bovine α_S2-casein. The minimum inhibitory concentration (MIC) of Cp1 and Cp2 were determined against a range of bacterial cultures. Cp1 exhibited an MIC of 125 μg mL⁻¹ against all Gram-positive bacteria tested, and MIC ranging between 125 and >1000 μg mL⁻¹ against the Gram-negative bacteria tested. Cp2 was generally far more potent against the Gram-positive bacteria, exhibiting an MIC of 21 μg mL⁻¹, compared to MICs ranging from 332 to >664 μg mL⁻¹ against most of the Gram-negative bacteria tested.     

Aluminium in foodstuffs

The aluminium content of a comprehensive food assortment typical of German nutritional habits was determined within the framework of market basket studies. Carried out in 1988 and 1991, a total of 128 items out of 12 groups of foodstuffs were included in this investigation. Aluminium content of the food assortment was low and comparable with literature data. Most investigated foodstuffs contained <5 μg Al g⁻¹ FM. Highest concentrations were determined in cocoa/cocoa products (33 μg g⁻¹), spices (145 μg g⁻¹) and black tea leaves (899 μg g⁻¹). In general, aluminium content of frequently consumed food, increased in the following order: beverages, food of animal origin, food of plant origin. With this low level of aluminium concentration in food, there is no danger of aluminium exposure in healthy persons.     

Production of volatile aroma compounds by kefir starter cultures

Production of carbonyl compounds by single-strain cultures, kefir starter (Lactobacillus delbrueckii subsp. bulgaricus HP1+Lb. helveticus MP12+Lactococcus lactis subsp. lactis C15+Streptococcus thermophilus T15+Saccharomyces cerevisiae A13) and kefir grains during fermentation and storage of kefir was studied. The content of carbonyl compounds produced by kefir starter was greater than that produced by kefir grains. The maximum acetaldehyde concentration (18.3 μg g⁻¹) in kefir with starter culture was mainly due to the metabolic activity of Lb. delbrueckii subsp. bulgaricus HP1 isolated from kefir grains. The highest diacetyl production activity was recorded in the starter culture (1.87 μg g⁻¹) and the single-strain culture St. thermophilus T15 (1.62 μg g⁻¹), followed by Lb. helveticus MP12 (0.85 μg g⁻¹) and Lc. lactis subsp. lactis C15 (0.42 μg g⁻¹). The lactobacilli Lb. delbrueckii subsp. bulgaricus HP1 and Lb. helveticus MP12 produced acetone, which was not found in the cocci cultures. The presence of 2-butanone was related to the production ability of Lb. helveticus MP12. In comparison, Lc. lactis subsp. lactis C15 synthesized ethyl acetate more actively than the other single-strain cultures included in the starter. S. cerevisiae A13 produced ethanol and CO₂ in amounts (3975 μg g⁻¹; 1.80 g L⁻¹) that lent cultured kefir distinctive flavour and aroma characteristic of authentic kefir.     

Comparison of multiple chemical sanitizers for reducing Salmonella and Escherichia coli O157:H7 on spinach (Spinacia oleracea) leaves

Effectiveness of multiple chemical sanitizers on the reduction of Salmonella spp. and Escherichia coli O157:H7 on spinach was compared. Fresh spinach (Spinacia oleracea) was inoculated with a bacterial suspension containing multiple strains of rifampin-resistant Salmonella and E. coli O157:H7. Inoculated spinach leaves were treated with a water wash or water wash followed by 2% L-lactic acid at 55 °C, peroxyacetic acid (80 mg/L), calcium hypochlorite (200 mg/L), ozonated water (mg/L) or ClO₂ gas (1.2 or 2.1 mg/L). The l-lactic acid produced a 2.7 log CFU/g reduction for E. coli O157:H7 and a 2.3 log CFU/g reduction for Salmonella, statistically significant compared to water wash alone (P < 0.05), which resulted in a reduction of 0.7 log CFU/g for both pathogens. These findings indicate that 2% l-lactic acid at 55 °C may be an effective treatment for reducing pathogens on spinach leaves.     

Fate of acid-adapted and non-adapted Escherichia coli O157:H7 inoculated post-drying on beef jerky treated with marinades before drying

The objective of the present study was to investigate survival of acid-adapted and non-adapted E. coli O157:H7 inoculated after drying on beef jerky that was treated with marinades before drying. Beef slices were not marinated before drying (control—C), or subjected to the following marinades (24 h, 4°C) prior to drying at 60°C for 10 h: (1) traditional marinade (TM), (2) double the amount of TM modified with added 1.2% sodium lactate, 9% acetic acid, and 68% soy sauce with 5% ethanol) (MM), (3) dipping into 5% acetic acid followed by TM (AATM), and (4) dipping into 1% Tween 20 and then into 5% acetic acid followed by the TM (TWTM). Dried slices were inoculated with acid-adapted or non-adapted E. coli O157:H7 (c. 6.2 log cfu cm⁻²) prior to aerobic storage at 25°C for 60 days. Survivors were determined using tryptic soy agar with 0.1% pyruvate, modified eosin methlylene blue agar, and sorbitol MacConkey agar. Results indicated that bacterial populations decreased during storage in the order of predrying marinade treatments TWTM⩾AATM>MM>C⩾TM. Populations decreased faster on jerky inoculated with acid-adapted cultures than with non-adapted cultures in all treatments. A 5.0 log reduction in bacterial counts was achieved within 7 days (TWTM and AATM) or never achieved during the 60 days storage period (C, TM). The earliest elimination (enrichment negative) of the pathogen occurred by 28 days (TWTM, ATTM and MM) in products inoculated with acid-adapted cultures and by 42 days (TWTM and AATM) in products inoculated with non-adapted cultures. It is concluded that under the conditions of this study, modified marinades and low water activity provide antimicrobial effects against possible post-processing contamination of beef jerky with E. coli O157:H7. Acid adaptation of cultures enhanced their inactivation during storage.     

Development of an immunosensor based on surface plasmon resonance for enumeration of Escherichia coli in water samples

An immunosensor for the rapid, sensitive and selective detection of generic Escherichia coli in water samples was developed on the basis of surface plasmon resonance (SPR). Antibodies against E. coli were immobilized on a sensor surface and water samples with different concentrations of E. coli were injected to the flow cell. The changes in the response unit (RU) due to the binding of different concentrations of bacteria were computed and a linear correlation (R² = 0.976) was obtained between log E. coli concentration and the change in the RU with a working range of 9 × 10¹ and 1.8 × 10⁵ cfu ml⁻¹. The complete regeneration of the sensor surface was realized by using 1% SDS solution. The selectivity of the developed sensor was examined with Enterobacter aerogenes and Enterobacter dissolvens which did not produce any significant response. The ability of the developed sensor to detect E. coli in real water samples was investigated and the results were closed to that obtained from plate counting method. Based on these results, the developed immunosensor can be employed for rapid, label-free, sensitive and selective detection of E. coli in water samples.     

Antioxidant properties of methanolic extracts from Ganoderma tsugae

Ganoderma tsugae Murrill was available in the form of mature and baby Ling chih, mycelia and fermentation filtrate. From these four forms, methanolic extracts were prepared and their antioxidant properties were studied. Methanolic extracts from mature and baby Ling chih showed high antioxidant activities (96.8% and 93.6%) at 20 mg ml⁻¹, and had EC₅₀ values of 0.53 and 1.11 mg ml⁻¹, respectively. EC₅₀ values in reducing power were 5.00, 2.28, 0.93 and 2.15 mg ml⁻¹ for Ling chih, baby Ling chih, mycelia and filtrate, respectively. Methanolic extracts from mature and baby Ling chih scavenged 1,1-diphenyl-2-picrylhydrazyl radicals by 88.4% and 93.8% at 5 mg ml⁻¹, whereas those from mycelia and filtrate scavenged by 85.7% and 79.3% at 10 mg ml⁻¹, respectively. EC₅₀ values in chelating ability on ferrous ions were 4.82, 3.05, 1.10 and 3.41 mg ml⁻¹ for Ling chih, baby Ling chih, mycelia and filtrate, respectively. Total phenols were the major naturally occurring antioxidant components found in all methanolic extracts and in the range of 24.0–35.6 mg g⁻¹. Based on EC₅₀ values, G. tsugae was good in antioxidant properties except for the scavenging ability on hydroxyl radicals.