An investigation of indirect conductimetry for detection of some food-borne bacteria

Cydonia oblonga M., A Medicinal Plant Rich in Phytonutrients for Pharmaceuticals

Cydonia oblonga M. is a medicinal plant of family Rosaceae which is used to prevent or treat several ailments such as cancer, diabetes, hepatitis, ulcer, respiratory, and urinary infections, etc. Cydonia oblonga commonly known as Quince is rich in useful secondary metabolites such as phenolics, steroids, flavonoids, terpenoids, tannins, sugars, organic acids, and glycosides. A wide range of pharmacological activities like antioxidant, antibacterial, antifungal, anti-inflammatory, hepatoprotective, cardiovascular, antidepressant, antidiarrheal, hypolipidemic, diuretic, and hypoglycemic have been ascribed to various parts of C. oblonga. The polysaccharide mucilage, glucuronoxylan extruded from seeds of C. oblonga is used in dermal patches to heal wounds. This review focuses on detailed investigations of high-valued phytochemicals as well as pharmacological and phytomedicinal attributes of the plant.

Antimicrobial Characteristics of Heated Eggshell Powder

Eggshells have high bioavailability and can be used as a source of calcium. The main component is CaCO3, which, when heated, is converted to CaO. Seashells are also mainly composed of CaCO3 and were previously found to exhibit antimicrobial activity after being heated. In this study, heated eggshell powder (HESP) was found to have antimicrobial activity against bacterial vegetative cells, fungi and bacterial spores. Parameters, such as the minimum inhibitory concentration, were determined with kinetic analysis using an indirect conductimetric assay. Moreover, HESP was able to kill the Bacillus subtilis spores. There were no significant differences in the activity between HESP, heated scallop-shell powder and pure CaO. The MIC values for HESP against bacteria and fungi were 0.29-0.43 and 1.3-1.5 mg/mL, respectively. Against B. subtilis spores, a reduction of two orders of magnitude of viability was confirmed following 20 min of treatment at 10 mg/mL at 60 ℃. The active oxygen generated from the HESP slurry was examined with chemiluminescence. The intensity of this increased with increasing concentrations of the HESP slurry. This suggests that HESP could be used as a natural antimicrobial agent. Although a high pH is the main contributor to this antimicrobial activity, active oxygen species generated from HESP are likely to be the main antimicrobial agents..

Application of bacteriophages for detection of foodborne pathogens

Bacterial contamination of food products presents a challenge for the food industry and poses a high risk for the consumer. Despite increasing awareness and improved hygiene measures, foodborne pathogens remain a threat for public health, and novel methods for detection of these organisms are needed. Bacteriophages represent ideal tools for diagnostic assays because of their high target cell specificity, inherent signal-amplifying properties, easy and inexpensive production, and robustness. Every stage of the phage lytic multiplication cycle, from the initial recognition of the host cell to the final lysis event, may be harnessed in several ways for the purpose of bacterial detection. Besides intact phage particles, phage-derived affinity molecules such as cell wall binding domains and receptor binding proteins can serve for this purpose. This review provides an overview of existing phage-based technologies for detection of foodborne pathogens, and highlights the most recent developments in this field, with particular emphasis on phage-based biosensors.

Biosensors and bio-based methods for the separation and detection of foodborne pathogens

The safety of our food supply is always a major concern to consumers, food producers, and regulatory agencies. A safer food supply improves consumer confidence and brings economic stability. The safety of foods from farm-to-fork through the supply chain continuum must be established to protect consumers from debilitating, sometimes fatal episodes of pathogen outbreaks. The implementation of preventive strategies like hazard analysis critical control points (HACCP) assures safety but its full utility will not be realized unless supportive tools are fully developed. Rapid, sensitive, and accurate detection methods are such essential tools that, when integrated with HACCP, will improve safety of products. Traditional microbiological methods are powerful, error-proof, and dependable but these lengthy, cumbersome methods are often ineffective because they are not compatible with the speed at which the products are manufactured and the short shelf life of products. Automation in detection methods is highly desirable, but is not achievable with traditional methods. Therefore, biosensor-based tools offer the most promising solutions and address some of the modern-day needs for fast and sensitive detection of pathogens in real time or near real time. The application of several biosensor tools belonging to the categories of optical, electrochemical, and mass-based tools for detection of foodborne pathogens is reviewed in this chapter. Ironically, geometric growth in biosensor technology is fueled by the imminent threat of bioterrorism through food, water, and air and by the funding through various governmental agencies.

Performance evaluation of a low conductive growth medium (LCGM) for growth of healthy and stressed Listeria monocytogenes and other common bacterial species

The performance of a low conductive growth medium (LCGM) (conductivity of <1300 microS) was evaluated for its ability to support growth of food borne bacterial pathogens including Listeria monocytogenes and to determine the expression of the two key virulence proteins in L. monocytogenes for possible applications in an impedance-based microfluidic biochip detection platform. Growth of Listeria was monitored spectrophotometrically and the lag phase, generation time, growth rate and maximum population density were determined using the Gompertz equation. LCGM had a lag phase of 2.3 h and showed a higher cell density compared to Luria Bertini (LB) broth. Length of lag phase was highly dependent on initial inoculum concentrations. The changes in conductivity with respect to growth in the low conductive medium were monitored using a conductivity probe. L. monocytogenes growth could be detected within 2 h (0.1 mS) in LCGM and within 6 h in LB. The performance of the media was also evaluated for the recovery of Listeria cells exposed to various stresses as 42 degrees C for 1, 2 or 6 h, an osmotic stress in 10.5% NaCl, an acidic stress at pH 2, 3 or 5 and a combined stress of 10.5% NaCl, pH 5 and 1 h exposure at 42 degrees C. The recovery rate was comparable with that of Tryptic soy broth containing yeast extract (TSBYE). L. monocytogenes in LCGM supported the expression of two key virulence markers, actin polymerization protein (ActA) and internalin B (InlB), which could be detected using specific antibodies. In general LCGM also supported the growth of several other bacterial species suggesting its implication in microbial quality monitoring of products. In conclusion, LCGM is a sensitive low conductive medium that supports the growth as well as the expression of virulence markers for potential applications in sensitive detection of L. monocytogenes or other food borne pathogens in impedance-based sensor platform.

Quantitative evaluation of antifungal activity of metallic oxide powders (MgO, CaO and ZnO) by an indirect conductimetric assay

AIMS

To evaluate antifungal activities of MgO, CaO and ZnO powders quantitatively by indirect conductimetric assay.

METHODS AND RESULTS

Candida albicans NBRC1060, Saccharomyces cerevisiae NBRC1950, Aspergillus niger NBRC4067 and Rhizopus stolonifer NBRC4781 were used as test micro-organisms. The indirect conductimetric assay, in which the change in electrical conductivity of an alkaline solution (NaOH) is produced by absorption of CO2 from microbial metabolism, could offer a simple and rapid evaluation of the antifungal activity within 24-48 h. The conductivity curves obtained for MgO, CaO and ZnO were analysed using the growth inhibition kinetic model proposed by Takahashi for calorimetric evaluation, and the kinetic parameters and minimum inhibitory concentration ([I]100) could be determined. MgO and CaO powders exhibited the antimicrobial activities against all fungi used in this study and showed little differences between types of fungi. However, although ZnO powder inhibited fungal growth, the values of [I]100 were over 100 mg ml-1.

CONCLUSIONS

Although a common method for evaluating antifungal activity requires over 5-7 days, the indirect assay could provide a rapid and quantitative evaluation of antifungal activity within approx. 2 days, and MgO and CaO were found to have antifungal activities.

SIGNIFICANCE AND IMPACT OF THE STUDY

The indirect assay can be applicable for simple and rapid evaluation of the antimicrobial activity of insoluble or slightly soluble materials with high turbidity such as antibacterial ceramic powders. Moreover, these materials can be useful for controlling fungi in food processing and the environment.

Measurement of fungi by an indirect conductimetric assay

AIMS

To investigate the growth of fungi using an indirect conductimetric assay and derive, experimentally and theoretically, the relationship between microbial concentration and electrical conductivity change.

METHODS AND RESULTS

The indirect assay, in which change in electrical conductivity of an alkaline solution (NaOH) is produced by absorption of CO2 from microbial metabolism, was conducted with the Bactometer (bioMerieux, Marcy-l'Etoile, France) for the enumeration of fungi. A linear relationship was obtained between detection time and logarithmic initial microbial concentration. This indirect assay used growth media, which could not be used in the direct conductimetric assay, to monitor fungal growth.

CONCLUSIONS

The indirect assay does not depend on the growth media and the turbidity of sample and could offer a simple and rapid assay for the measurement of fungal growth under various conditions.

SIGNIFICANCE AND IMPACT OF THE STUDY

The indirect assay is applicable for rapid detection of fungi, estimation of the growth rate and evaluation of antifungal activity.

Curvularia haloperoxidase: antimicrobial activity and potential application as a surface disinfectant

A presumed antimicrobial enzyme system, the Curvularia haloperoxidase system, was examined with the aim of evaluating its potential as a sanitizing agent. In the presence of hydrogen peroxide, Curvularia haloperoxidase facilitates the oxidation of halides, such as chloride, bromide, and iodide, to antimicrobial compounds. The Curvularia haloperoxidase system caused several-log-unit reductions in counts of bacteria (Pseudomonas spp., Escherichia coli, Serratia marcescens, Aeromonas salmonicida, Shewanella putrefaciens, Staphylococcus epidermidis, and Listeria monocytogenes), yeasts (Candida sp. and Rhodotorula sp.), and filamentous fungi (Aspergillus niger, Aspergillus tubigensis, Aspergillus versicolor, Fusarium oxysporum, Penicillium chrysogenum, and Penicillium paxilli) cultured in suspension. Also, bacteria adhering to the surfaces of contact lenses were killed. The numbers of S. marcescens and S. epidermidis cells adhering to contact lenses were reduced from 4.0 and 4.9 log CFU to 1.2 and 2.7 log CFU, respectively, after treatment with the Curvularia haloperoxidase system. The killing effect of the Curvularia haloperoxidase system was rapid, and 10(6) CFU of E. coli cells/ml were eliminated within 10 min of treatment. Furthermore, the antimicrobial effect was short lived, causing no antibacterial effect against E. coli 10 min after the system was mixed. Bovine serum albumin (1%) and alginate (1%) inhibited the antimicrobial activity of the Curvularia haloperoxidase system, whereas glucose and Tween 20 did not affect its activity. In conclusion, the Curvularia haloperoxidase system is an effective sanitizing system and has the potential for a vast range of applications, for instance, for disinfection of contact lenses or medical devices.

An indirect conductimetric screening method for the detection of antibiotic residues in bovine kidneys

An indirect conductimetric screening method using three test bacterium-medium combinations was developed for rapid detection of antibiotic residues in bovine carcasses. The detection time (DT), i.e. the point when the growth of the test bacterium was detected, was determined by observing the rate of change in the conductance plotted against time. This detection time averaged half of the reference time recorded by the instrument software. Total change in conductance (TC) was used as a further measure of growth. Threshold values for DT and TC were determined with inhibitor-free kidney samples. The presence of a residue was indicated if the DT exceeded the respective threshold value and was confirmed if the TC remained below the TC threshold value. The limits of detection (LODs) determined with fortified samples were at about or below the MRLs for cephalexin, chlortetracycline, ciprofloxacin, dihydrostreptomycin, enrofloxacin, oxytetracycline and penicillin G. The LODs for penicillin G, oxytetracycline and the sum of enrofloxacin and ciprofloxacin were also estimated with incurred samples; these samples were also analysed using liquid chromatography. The LODs determined with fortified and incurred samples were in close agreement. Given its rapid detection, good sensitivity to a wide range of antibiotics and ease of performance, the indirect conductimetric method developed here would seem to offer an appealing alternative to agar diffusion tests.

Strategies in the development of media for the detection of food-borne pathogens

Successful medium development is dependent on using a systematic approach and also by giving due consideration to the factors which can influence the performance of the medium at the various stages of assessment. The most important factors to be considered are: (i) the properties of the target organisms, (ii) the selection of test strains, (iii) the methods of evaluation, (iv) the basal medium and growth supplements, (v) the properties of the medium, and (vi) the intended use of the medium. If these are investigated fully then culture media can be optimised to fulfil the demands of modem microbiology techniques used for detection and confirmation of bacteria.

Enzymatic removal and disinfection of bacterial biofilms

Model biofilms of Staphylococcus aureus, Staphylococcus epidermidis, Pseudomonas fluorescens, and Pseudomonas aeruginosa were made on steel and polypropylene substrata. Plaque-resembling biofilms of Streptococcus mutans, Actinomyces viscosus, and Fusobacterium nucleatum were made on saliva-coated hydroxyapatite. The activity of enzymes against bacterial cells in biofilm was measured by fluorescence microscopy and an indirect conductance test in which evolution of carbon dioxide was measured. Glucose oxidase combined with lactoperoxidase was bactericidal against biofilm bacteria but did not remove the biofilm from the substrata. A complex mixture of polysaccharide-hydrolyzing enzymes was able to remove bacterial biofilm from steel and polypropylene substrata but did not have a significant bactericidal activity. Combining oxidoreductases with polysaccharide-hydrolyzing enzymes resulted in bactericidal activity as well as removal of the biofilm.

A method and medium for the electrical detection of Listeria spp. from food

The development of a liquid medium for the detection of Listeria spp. by capacitance monitoring of food samples previously enriched in UVM 1 broth is described. Rapid growth of Listeria monocytogenes was shown to occur in liquid media with selectivity based on antibiotics found in Oxford agar. The final capacitance medium contained higher concentrations of the Oxford selective agents than Oxford agar and did not require the esculin/ferric ammonium citrate reaction to be observed. The medium relied upon the ability of Listeria spp. to induce a greater than 30% change in capacitance within 30 h. When run in parallel with the Listeria spp. test samples of a large food company, the method gave far fewer false-positive results than Fraser broth.

Use of indirect conductimetry to predict the growth of spoilage yeasts, with special consideration of Zygosaccharomyces bailii

In recent years, modeling for the purpose of predicting microbiological spoilage of foods has gained much interest. Predictive modeling requires a concentrated mathematical and experimental approach; to collect data of adequate quality is a technically demanding task when several experimental parameters are involved. Rapid, non-traditional, automated techniques are particularly useful in modeling. Of these, electrometric techniques appear to be most promising. Indirect conductimetry was used to study the effect of temperature, aw, pH and potassium sorbate concentration on the growth of Zygosaccharomyces bailii. The automated Malthus 2000 instrument proved to be convenient for gathering a large amount of data that were then used to develop polynomial models describing the response of the yeast to combinations of experimental factors in terms of conductimetric detection time and maximum rate of change in conductance. Results demonstrated that indirect conductimetry is suitable for monitoring the effect of environmental factors on the growth and activity of Z. bailii and perhaps other food spoilage yeasts.

Detection of Salmonella in animal protein by Rappaport-Vassiliadis broth using indirect impediometry

Indirect impedance methodology for the detection of Salmonella was investigated using a rapid automated bacterial impedance technique (RABIT) system. Four commercially available Rappaport-Vassiliadis (RV) enrichment broths were evaluated for their sensitivity and selectivity in detecting Salmonella using this technique. The RV from Lab M and Oxoid (new) gave the shortest detection times and showed good correlation between Salmonella numbers and detection times. Using Lab M medium, the indirect impedance technique could distinguish between Salmonella spp. and the closely related genera, Proteus and Citrobacter. The impedance technique showed recoveries of Salmonella from processed animal protein and raw meats equivalent to, or better than, those obtained with RV used in a conventional Salmonella isolation procedure.

Impedance detection of Salmonella in processed animal protein and meat

The impedance technique showed a detection rate (95%) equal to that of conventional enrichment for raw meat contaminated with Salmonella. For processed animal protein samples impedance was less sensitive. A commercially available Easter and Gibson impedance medium used for the selective enrichment of salmonellae proved superior to the laboratory prepared equivalent for the detection of Salmonella in processed animal protein. The rate of false-positive results with the impedance technique was high.