Detection of salmonellas in confectionery products by conductance

A modified lysine decarboxylase broth has been developed which could be used with a Bactometer M123 to differentiate salmonellas from other bacteria by the characteristics of the conductance detection curve. The medium was used in combination with a selenite cystine trimethylamine oxide dulcitol medium to screen 50 strains of salmonellas and 42 strains of other organisms to establish detection curve magnitude and rate values which could be used to identify curves specific to salmonellas. The combination of media detected all salmonellas tested except Salmonella pullorum. The two media were used to screen 100 inoculated product samples with the Bactometer instrument, in parallel with traditional plating procedures, and using various combinations of pre-enrichment and selective enrichment incubation periods. After 24 h pre-enrichment, the Bactometer system detected more positive samples than the conventional plating procedures after pre-enrichment and selective enrichment. It is considered that these media used in parallel in the Bactometer after conventional pre-enrichment could provide a 48 h screening procedure for salmonellas with a sensitivity comparable to present plating procedures.     

Detection of salmonellas in confectionery products by conductance

A modified lysine decarboxylase broth has been developed which could be used with a Bactometer M123 to differentiate salmonellas from other bacteria by the characteristics of the conductance detection curve. The medium was used in combination with a selenite cystine trimethylamine oxide dulcitol medium to screen 50 strains of salmonellas and 42 strains of other organisms to establish detection curve magnitude and rate values which could be used to identify curves specific to salmonellas. The combination of media detected all salmonellas tested except Salmonella pullorum . The two media were used to screen 100 inoculated product samples with the Bactometer instrument, in parallel with traditional plating procedures, and using various combinations of pre-enrichment and selective enrichment incubation periods. After 24 h pre-enrichment, the Bactometer system detected more positive samples than the conventional plating procedures after pre-enrichment and selective enrichment. It is considered that these media used in parallel in the Bactometer after conventional pre-enrichment could provide a 48 h screening procedure for salmonellas with a sensitivity comparable to present plating procedures.     

Improvements to a lysine medium for detection of salmonellas by elctrical conductance

Improvements in performance of a lysine conductance medium for the detection of salmonellas were achieved from a study of the effects of its various components. When sodium biselenite was included as an inhibitor for non-salmonella organisms conductance signals were depressed. The inclusion of sodium chloride reduced this toxicity and improved conductance responses. Increasing the pH to pH 7.0 prevented the medium becoming too acidic and inhibitory to salmonellas. The new medium detected 70-0% of salmonella-positive animal protein samples.     

The effect of air on the response of salmonellas in conductance media

The effect of air on the conductance response of salmonellas in three selective media was investigated. When assays were carried out aerobically, the time to observe a presumptive positive in all media was reduced and the conductance change was larger than in assays done under microaerophilic conditions. Low (10²/ml) numbers of pre-enriched salmonellas were detected only under aerobic conditions.     

Evaluation of Nigerian animal feeds by particle-induced X-ray emission

There is need to evaluate the locally available animal feeds in Nigeria so as to be able to combine them in acceptable proportions to the animals to achieve the desired growth rate. The technique of particle-induced X-ray emission (PIXE) was employed for the evaluation of these locally available animal feeds, which include Panicum maximum (Guinea grass), Cynodon plectostachyum (grass), Leucaena leucephala (legume), Calopogonium mucunoides (legume), Gliricidia sepium (legume), Euphorbia polychrome (legume), Pueraria phaseloides (legume), and Centrosema pubescens (legume). The proton beam delivered by the 2.5-MV AN 2000 Van de Graaff accelerator at the International Centre for Theoretical Physics Laboratori Nazionali di Legnaro (LNL), Padova, Italy was used for the PIXE measurements. Twenty-one different elements were detected at various concentrations and their nutritional effects on different animals are discussed.     

Some modification to the media for rapid automated detection of salmonellas by conductance measurement

A selenite medium for the automated detection of salmonellas by conductance measurements has been modified to eliminate the negative results given by some dulcitol-negative strains. The dulcitol is replaced with mannitol and pre-enrichment is best done in buffered peptone water containing mannitol and dimethylsulphoxide. It is suggested that both versions of the selenite medium be used initially.     

A complete protocol using conductance for rapid detection of salmonellas in confectionery materials

Increased confidence in conductimetric detection of salmonellas was achieved by combining a bacteriophage-based test with use of a selenite cystine trimethylamine oxide dulcitol medium and a modified lysine decarboxylase broth. All 81 Salmonella isolates tested were detected and few of the 39 non-salmonellas gave false positives. Results from the screening of 43 inoculated product samples further support the use of this simple, rapid method for routine salmonella testing in the food industry.     

The growth of salmonellas in hydrated animal feed supplemented with antibiotics

The growth of antibiotic-sensitive salmonellas in hydrated animal feed incubated at 37°C was relatively unaffected by high concentrations (> 800 ppm) of bacteriostatic agents such as chlortetracycline. On the other hand, they were killed by low concentrations (< 50 ppm) of bactericidal agents such as ampicillin or furazolidone. The aminoglycoside antibiotics apramycin and neomycin killed the salmonellas when present at concentrations in excess of those likely to be recommended for therapeutic purposes (> 300 ppm).     

Determination of the concentration of metals in animal feeds

The concentrations of eight metals (Cd, Cr, Cu, Fe, Mn, Ni, Pb, and Zn) were determined by atomic absorption spectrophotometry for the following related materials: three products obtained by processing cattle manure—a cellulosic material resembling silage (CI), a water soluble protein-rich powder (CII), and a soil amendment product (CIII)—as well as dairy cattle feed rations containing CII and the resultant fresh feces; and the manure composites used to prepare the processed products. The concentrations of these metals generally increased in samples in the order feed, feces, CI, CII, and CIII. The metal concentrations in CI were comparable to literature values for silage; the metals in CII were present at higher concentrations, but not sufficient to limit its use as a feed ingredient. The potential health effects of feeding cattle rations containing CI or CII are discussed in the context of these results.     

Detection of salmonellas by DNA hybridization with a fluorescent alkaline phosphatase substrate

R. J. CANO, M.J. TORRES, R.E. KLEM, J.C. PALOMARES AND J. CASADESUS. 1992. This study evaluates a DNA hybridization assay for salmonella with A tto P hos ™ (JBL Scientific, San Luis Obispo, CA), a fluorescent substrate for alkaline phosphatase. The probe used (50 ng/ml) was a biotinylated 600 bp fragment consisting of a tandem repeat of an insertion sequence (IS200) found in most Salmonella spp. evaluated. The hybridization was carried out at 65°C for 2 h without prior prehybridization and hybrids were detected by the addition of a streptavidin-alkaline phosphatase conjugate. Circles (5 mm) were cut from the membrane and placed in a cuvette containing 1 ml of 1 mmol/1 A tto P hos ™. The reaction was evaluated after 30 min at 37°C with a fluorometer with an excitation wavelength of 440 nm and an emission wavelength of 550 nm. The sensitivity of the probe was estimated to be 10 000 copies of target DNA or 5 times 10^-20 mol of DNA. All 74 salmonella strains tested reacted with the probe but none of the 98 heterologous species tested gave positive results. The results of this study indicate that our assay method, which employs a biotinylated tandem repeat of IS200 and A tto P hos ™, is a specific and highly sensitive quantitative method for the detection of salmonellas.     

Niacin assay by monitoring changes in electrical conductance caused by microbial growth

A computerized Malthus 128 H Growth Analyser was used to determine the changes in conductance produced by growth of a niacin-dependent strain of Lactobacillus plantarum ATCC 8014 in different concentrations of niacin in the growth medium. Changes in conductance varied linearly with the niacin concentration in the range 5-50 ng/ml. The time required to complete a test is inversely related to the inoculum size, and results can be obtained after 6 h.     

Niacin assay by monitoring changes in electrical conductance caused by microbial growth

A computerized Malthus 128 H Growth Analyser was used to determine the changes in conductance produced by growth of a niacin-dependent strain of Lacto-bacillus plantarum ATCC 8014 in different concentrations of niacin in the growth medium. Changes in conductance varied linearly with the niacin concentration in the range 5–50 ng/ml. The time required to complete a test is inversely related to the inoculum size, and results can be obtained after 6 h.     

Detection of salmonellas by DNA hybridization with a fluorescent alkaline phosphatase substrate.

This study evaluates a DNA hybridization assay for salmonella with AttoPhos (JBL Scientific, San Luis Obispo, CA), a fluorescent substrate for alkaline phosphatase. The probe used (50 ng/ml) was a biotinylated 600 bp fragment consisting of a tandem repeat of an insertion sequence (IS200) found in most Salmonella spp. evaluated. The hybridization was carried out at 65 degrees C for 2 h without prior prehybridization and hybrids were detected by the addition of a streptavidin-alkaline phosphatase conjugate. Circles (5 mm) were cut from the membrane and placed in a cuvette containing 1 ml of 1 mmol/l AttoPhos. The reaction was evaluated after 30 min at 37 degrees C with a fluorometer with an excitation wavelength of 440 nm and an emission wavelength of 550 nm. The sensitivity of the probe was estimated to be 10,000 copies of target DNA or 5 x 10(-20) mol of DNA. All 74 salmonella strains tested reacted with the probe but none of the 98 heterologous species tested gave positive results. The results of this study indicate that our assay method, which employs a biotinylated tandem repeat of IS200 and AttoPhos, is a specific and highly sensitive quantitative method for the detection of salmonellas.     

Isolation of salmonellas by immunomagnetic separation

A.E.M. VERMUNT, A.A.J.M. FRANKEN AND R.R. BEUMER. 1992. Magnetisable particles, coated with anti-salmonella serum, were used to isolate Salmonella livingstone from pure cultures, mixed cultures and food samples. Beads (10⁷) were generally incubated with 10⁴ Salm. livingstone cells/ml for 60 min at room temperature. The incubation and washing medium (0.01 mol/l phosphate-buffered saline; PBS) contained 0.1% bovine serum albumin (BSA) and 0.1% Tween 20, respectively. This method gave a recovery for Salm. livingstone of 51.9±7.8%. However, other micro-organisms such as Aeromonas hydrophila interfered with this test because of non-specific reactions (recovery 50.9±12.7%). These non-specific reactions could be decreased by using 4% skim milk instead of 0.1% BSA in the incubation medium. The ratio of the recovery of Salim. livingstone relative to the recovery of Aer. hydrophila changed from 0.9 when PBS with 0.1% BSA was used, to 13.4 when PBS with 4% skim milk was used. Immunomagnetic separation of Salmonella spp. from food samples offers good prospects for concentrating salmonella cells from heterogeneous bacterial suspensions, such as enrichment broths.     

Concentrations of fumonisin B1 in feeds associated with animal health problems

Ninety-eight samples of feeds associated with 44 cases of equine leukoencephalomalacia (ELEM) and 83 samples of feed associated with 42 cases of a porcine pulmonary edema syndrome (PPE) were analyzed for fumonisin B₁ (FB₁). For comparison purposes, 51 feed samples not associated with PPE or ELEM were also analyzed. Feed associated with ELEM contained FB₁ ranging from less than 1 g/g to 126 g/g with 75% of the cases having at least 1 sample above 10 g/g. Feeds associated with PPE ranged from less than 1 g/g to 330 g/g with 71% of the cases having at least 1 sample greater than 10 g/g. Quantitation was by high performance liquid chromatography (HPLC)/fluorescence using the fluorescamine derivative with confirmation by thin layer chromatography (TLC) and/or gas chromatography/mass spectroscopy (GC/MS).     

The blockage of the electrical conductance in a pore-containing membrane by the n-alkanes.

1. In monooelein bilayers made highly conducting by the addition of a fixed amount of o-pyromellitylgramicidin, the membrane conductance has been shown to be strongly dependent on the chain length of the n-alkane with which the membrane is in equilibrium. Thus for n-hexadecane, the conductance is larger by approx. 10(4) times than it is for n-octane. This result is independent of whether the polypeptide is introduced via the aqueous or lipid phases. 2. The observed conductance variations have been accounted for in terms of a mechanism (outlined in earlier publications) which is based on the thickness and tension changes produced in bilayers by the adsorption of n-alkanes. Essentially quantitative agreement between theory and experiment is found.