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PubMed1978

Comparison of thin-layer chromatographic detection methods for histamine from food extracts.

The specificity and sensitivity of four visualization reagents, ninhydrin, o-phthalaldehyde (OPT), fluorescamine and o-diacetylbenzene (DAB), for the detection of histamine on thin-layer chromatograms developed in several optimal solvent systems were compared. While the ninhydrin reagent is the most sensitive with a detection limit of 0.4 nmoles of histamine, the DAB and fluorescamine reagents offer the most potential as histamine-specific visualization reagents. The OPT reagent was unsatisfactory because the fluorescent sports developed with this reagent were unstable. Of 19 amines tested in addition to histamine, ninhydrine reacted with 17, fluorescamine with 8 and DAB with 15. Since only histidyl-leucine, octopamine, serotonin and tryptophan interfere in the resolution of histamine in any of the solvent systems used, DAB provides some advantages by not reacting with histidyl-leucine. In addition, with the acetone-ammonia (95:5) solvent system, which adequately separates histamine from all other tested amines, no background interference problems were noted when using DAB as the visualization reagent. Background interference problems with the acetone-ammonia system were evident with the other visualization reagents. The sensitivity of the DAB and fluorescamine methods (4 nmoles of histamine) allows both reagents to act as semi-quantitative screening agents for potentially toxic levels of histamine in food extracts. With a variety of food samples, DAB visualization following development in acetone-ammonia (95:5) was the optimal thin-layer chromatographic method.

Chromatography, Thin Layer↗

PubMed1979

A modified pork plasma agar for the enumeration of Staphylococcus aureus in foods.

The coagulase reaction of Staphylococcus aureus on the PPSA (pork plasma for S. aureus) agar of Devoyod et al. was found to be fibrinogen-deficient. By including bovine fibrinogen (BFG) in the medium, the fibrin halos around S. aureus colonies became more distinct, preparations of pork plasma previously unacceptable for inclusion in the original PPSA agar were performing well, and the amount of pork plasma required in PPSA agar could be reduced by nearly 90%. In the modified medium, designated PPF (pork plasma fibrinogen) agar, the agar base (Baird-Parker agar without egg yolk) was unchanged. After surface plating, the base was covered with 8 mL of a modified overpour agar: 2.5% pork plasma, 0.38% BFG, and 0.0015% soy trypsin inhibitor in 0.7% Bacto agar. Most S. aureus strains could be enumerated after 24 h of incubation at 35 degrees C; the others required 44 h. Without soy trypsin inhibitor, a number of strains showed considerable fibrinolysis between 24 and 44 h of growth; this activity was neutralized by the inhibitor. The S. aureus counts of 27 food samples on PPF agar were essentially the same as the confirmed S. aureus counts obtained by the Baird-Parker method.

Agar↗

PubMed1977

Use of enzyme-labeled antibodies to detect Salmonella in foods.

An indirect enzyme-labeled antibody technique (ELAT), in which Salmonella typhimurium was used as a model, was developed as a method to detect Salmonella in food samples. A cellulose-acetate membrane filter, the matrix for detection, was placed on a membrane-filter base and overlaid with a multiwelled lucite template. Mixed broth enrichment cultures were dispensed in the template wells, and cells were spotted onto the membrane via suction. After fixation, the membranes were immersed in rabbit anti-S. typhimurium flagella antibody, washed, immersed in goat anti-rabbit antibody conjugated to peroxidase, and washed. Exposure of membranes to the substrates 3,3'-diaminobenzidine or benzidine resulted in development of brown or blue macroscopic reaction products, respectively, on spots containing S. typhimurium. ELAT results agreed with those of enrichment serology and cultural procedures on three food products containing known levels of S. typhimurium. Because of the magnification effect of the enzyme-substrate reaction, fewer cells were needed for detection than with enrichment serology, thereby reducing the total analysis time. The ability to test 14 or more samples simultaneously on a 47-mm membrane filter would facilitate screening large number of samples. Pending the development of a pure H antisera pool for the common Salmonella serotypes free from O antibodies, the ELAT demonstrated potential as a Salmonella detection methodology.

Antibodies, Bacterial↗

PubMed1978

Plating procedure for the enumeration of coliforms from dairy products.

A "repair-detection" procedure consisting of pour plating of food samples with Trypticase soy agar, followed by 1-h repair incubation at room temperature and subsequent overlay with violet red bile agar, was found to be an effective method for the detection of injuried and uninjuried coliforms from dairy products. This method was relatively less effective for the detection of coliforms in many semipreserved foods as compared with dairy products, but more effective than the most-probable-number method.

Bacteriological Techniques↗

PubMed1975

Dietary factors and esophageal cancer in the Caspian Littoral of Iran.

A study was undertaken to attempt to relate the distribution of exogenous factors to the varying incidences of esophageal cancer in the Caspian Littoral of Iran. For the study, 38 villages were chosen by random sampling in 14 regions defined by their esophageal cancer incidence and environmental characteristics. Information was obtained on the dietary, social, and cultural features of each village. In addition, an extensive 5-day study of 6 randomly selected households in each of the 38 villages was conducted. The study consisted of measured dietary intake, a historical food consumption questionnaire, and clinical examinations of adult occupants. Preliminary results show no single factor responsible for the etiology of esophageal cancer. However, there were some major dietary differences between the regions of different esophageal cancer risk. Bread was the chief staple food in high-incidence areas; rice, in low-incidence areas. In high-incidence areas, there was a low intake of vitamins A and C, riboflavin, animal protein, and fresh vegetables and fruit, but a greater consumption of sheeps and goat's milk. Analyses of food samples for aflatoxins, polycylic aromatic hydrocarbons, and nitrosamines showed low levels of these carcinogens in areas of high and low incidences. The use of tobacco and alcohol was not found to be of significance.

Alcohol Drinking↗

PubMed1979

Dichloran-rose bengal medium for enumeration and isolation of molds from foods.

Overgrowth by spreading molds such as Rhizopus and Mucor species is a problem with fungal enumeration media used for foods. Thirty-one antifungal compounds were surveyed for their ability to selectively inhibit such fungi while allowing growth of mycotoxigenic molds and other species of significance in food spoilage. Dichloran (2,6 dichloro-4-nitroaniline) restricted growth of Rhizopus stolonifer while allowing satisfactory growth of the other test molds. Three Rhizopus and Mucor species were encountered that were not inhibited by dichloran; these were controlled by the addition of rose bengal. The optimal medium, designated DRBC, contained 2 micrograms of dichloran and 25 micrograms of rose bengal per ml. DRBC, in pure culture tests and with food samples, restricted the colony size of spreading molds and recovered a wider range of species in higher numbers than other enumeration media.

Aniline Compounds↗

PubMed1978

Water supply and nutritional status in rural northern Nigeria.

A high incidence of protein energy malnutrition (PEM) was found in a community survey of preschool children in rural northern Nigeria among whom gastro-enteritis is common. Wasting (less than 80% Weight/Height) was more common (37.9%) among those with scanty, unprotected water supplies than in those with copious protected water (10.2%) whereas the incidence of stunting (less than 90% Height/Age)) was similar. Severe coliform contaminatin of all water sources was demonstrable. Even higher numbers of coliforms in foods sampled suggests that other factors related to water supply may be more important than water purity in the genesis of the PEM/gastro-enteritis complex.

Body Height↗

PubMed1978

Nutrient levels of some foods of Eskimos from Artic Bay, N. W.T., Canada.

Native food samples of caribou, seal, and arctic char were collected from resident Eskimos in Arctic Bay, N.W. T., and analyzed for nutrients. Caribou and seal meats were similar in protein and fat content in comparison with beef. Arctic char was above the average in protein and fat content for fish. Ascorbic acid was present in significant amounts only in baby seal liver. Thiamin, riboflavin, vitamin B12, folacin, and pantothenic acid content ranged from average to high for seal and carbiou meat, respectively, in comparison to published values for pork and beef. The vitamin B6 content of caribou meat was comparable to average values reported for pork and beef but was lower in seal meat. Baby seal liver contained similar levels of thiamin, riboflavin, vitamin B12, folacin, and pantothenic acid and less vitamin B6 than those reported for pork, beef, calf, and lamb liver. Arctic char was not appreciably different in these vitamins from other fish. The iron content of the Eskimo foods was higher than the meat group of the mixed Canadian diet. The macro mineral nutrients in these foods were comparable to those in beef and fish. The amino acid composition of caribou and seal meat was similar to beef, except that seal meat had a lower content of sulfur-containing amino acids and a much higher content of histidine. The sample of seal and arctic char were relatively high in concentrations of long-chain unsaturated fatty acids.

Amino Acids↗

PubMed1979

Salmonella isolation from hospital areas.

Evidence of the presence of salmonellas in a paediatric ward, a special care baby unit, a maternity unit and a hospital kitchen was obtained by culture of sewer swabs, faeces and food samples. The survey was designed to cause as little administrative interference as possible. The technical aspects of the survey did not strain laboratory facilities. Minimal secondary spread of salmonella infection was experienced.

Bacteriological Techniques↗

PubMed1976

Selenium in foods: evaluation of atomic absorption spectrometric techniques involving hydrogen selenide generation and carbon furnace atomization.

The performance of hydrogen selenide generation- and carbon furnace atomization-atomic absorption spectrometry, with a semiautomated trace metal accessory and a carbon rod atomizer, respectively, was evaluated for the determination of selenium in foods. Samples were digested with nitric, perchloric, and sulfuric acids for both procedures. Hydrogen selenide was generated with stannous chloride/potassium iodide/zinc from 20 ml aliquots in a hydrochloric-sulfuric acid medium and directed into an argon-hydrogen-entrained air flame. Sample matrix interferences in the carbon furnace technique were minimized by isolating selenium by precipitation with ascorbic acid and redissolution in nitric-perchloric acid prior to taking 5 mul aliquots for estimation; precision was significantly improved by incorporating 5000 mug nickel/ml into analytical solutions. For the hydrogen selenide and carbon furnace techniques, respectively, the following data were obtained for untreated standard solutions: sensitivity, 0.13 and 10.0 ng/ml; absolute sensitivity, 2.6 and 0.05 ng; detection limit, 0.4 and 90 ng/ml; absolute detection limit, 7 and 0.45 ng. The detection limit and absolute detection limit for samples were 2.5 ng/ml and 50 ng, respectively, for the hydrogen selenide method, and 25 ng/ml and 0.13 ng, respectively, for the carbon furnace method. Taking into consideration these figures and the practical aspects of both methods, the overall performance of the hydrogen selenide method was superior.

Evaluation Studies as Topic↗

PubMed1992

[Detection and identification of pathogenic bacteria by polymerase chain reaction with primers from DNA sequence of ribosomal RNA].

Applicability of the polymerase chain reaction method for identification of pathogenic bacteria was examined with the primers synthesized from the ribosomal RNA gene sequence containing both homologous and species-specific regions of bacterial species from Mycoplasma to Mycobacteria. Two out of the nine sets of promoters prepared, each covering about 650 nucleotides spanning from 16S RNA to 23S RNA regions, produced the corresponding DNA fragments from all the strains tested, and another set did so from all species but Mycoplasma. This method enabled one to detect and identify E. coli in a sample containing 2 x 10(2) CFU. The restriction enzyme patterns of the PCR products obtained with Hae-III, Hha-I, Mbo-I, Msp-I, Rsa-I and Taq-I were so characteristic as to differentiate one species from another. Ten strains of E. coli showed identical restriction patterns and 10 of S. aureus also showed identical patterns indicating that the restriction pattern is species-specific. The method may be applicable to detection and identification of a certain species bacteria which are suspected to be consealed in water or food samples, or clinical specimens, especially when the consealed bacterial genus or species can not be predicted.

Base Sequence↗

PubMed1976

Survey of food products for volatile N-nitrosamines.

A variety of food products containing nitrite were analyzed for 14 volatile N-nitrosamines by using a method demonstrated to be sensitive to 10 ppb. A total of 121 food samples were screened for volatile N-nitrosamine content. N-Nitrosopyrrolidine was confirmed in fried bacon at levels up to 139 ppb. N-Dimethylnitrosamine, N-nitrosopyrrolidine, and N-nitrosopiperidine were also confirmed in spice-cure mixtures at levels ranging from 50 to 2000 ppb.

Dimethylnitrosamine↗

PubMed1979

Antibiotic resistance of salmonellae in Czechoslovakia -- situation and prospects.

Antibiotic resistance of non-typhoid Salmonellae is in Czechoslovakia continuously monitored by a computer and its transferability is studied, on an all-nation level, within the Federal Plan of Scientific Investigation and Development. Restance and its transferability was surveyed in strains of Salmonella from humans, from farm animals, from the food chain as well as from surface and waste waters. Proportion of antibiotic-resistant Salmonella strains did not, in general, increase during the four-year period of 1973 to 1977. While resistant strains from humans as well as farm animals show a high degree of transferability, strains from food samples lack, in general, the transfer ability. This might be inferred that strains causing human salmonellosis which are carried to man trough foodchain, gain their character of transferability directly in the gut, i.e. from E. coli strains, and mainly due to presence of therapeutically given antibiotics.

Animals↗

PubMed1992

Laboratory performance in a food microbiology proficiency testing scheme.

Results from two shipments in a proficiency testing scheme in which almost 200 food microbiology laboratories participated are summarized. Freeze-dried mixtures of bacteria were used as simulated food samples. Four and six samples, respectively, were examined. The statistical procedures used to evaluate the performance of participating laboratories are described. It is shown that laboratories which had been in the scheme for a long time perform, on average, better than those that had been in the scheme for a short time. The former laboratories produced fewer false and outlying results, and were more accurate and precise in their determinations.

Bacteria↗

PubMed1976

Evaluation of an automated fluorescent antibody procedure for detection of Salmonella in foods and feeds.

A prototype automated system using fluorescent antibody (FA) was evaluated for rapid detection of salmonellae in foods. Samples were enriched in selenite cystine and tetrathionate broths. After incubation, both were transferred into fresh selenite cystine for a 4-h "post-enrichment" to dilute possible background fluorescence from product. These cultures were then analyzed automatically, and results were compared with those obtained by the methods of the Association of Official Analytical Chemists (AOAC). Initially, 167 samples of milk powder, dried yeast, and imported frog legs were examined. The AOAC and automated FA methods correlated well with all samples but frog legs. Difficulty with the latter was caused by procedural and mechanical problems coupled with high numbers of competing microorganisms in post-enrichment cultures. Modification of procedure and partial redesign of equipment corrected these difficulties, and excellent correlation was obtained with another 116 frog leg samples. All 89 AOAC-confirmed positives were also detected by the automated FA method, and there were only 4% false FA positives. The system shows potential for screening products for salmonellae; however, all positives should be confirmed by manual biochemical and serological methods.

Animal Feed↗

PubMed1979

[The occurrence of cadmium in some types of food].

An examination of 732 samples of foods of animal and vegetable origin revealed that 95% sea fish products, 94% samples of sea and fresh-water fish, 69.9% samples of foods of vegetable origin and 32.9% samples of foods of animal origin -- tinned beefand pork -- pâtés and spreads -- did not comply with the requirements of the standard on contaminants in foods for cadmium content. Together with the investigation of cadmium content in foods the applied method of atomic absorption spectrophotometry was tested, from the point of interferences during establishing the actual cadmium content; at the same time, this study concerned cadmium losses during the process of mineralization of the biologic material samples. It was concluded that the measured cadmium values were affected by the presence of a higher content of sodium chloride in the samples. The re-gained yield of cadmium by the used method of mineralization is 85%.

Animals↗

PubMed2026

Insights into the fate and dynamics of antibiotic resistance in multidrug-resistant Bacillus cereus during in vitro simulated gastrointestinal digestion.

Bacillus cereus, an important pathogen responsible for causing foodborne diseases worldwide, releases pore-forming enterotoxins, which target host epithelial cells, leading to osmotic lysis and ultimately manifesting as diarrheal syndrome. Moreover, some B. cereus strains carry antimicrobial resistance genes that confer multidrug resistance against a spectrum of antibiotics. Characterizing the survival traits of multidrug-resistant (MDR) B. cereus strains in the intestinal microenvironment is essential for developing targeted strategies to effectively manage diarrheal foodborne diseases caused by this pathogen. This study used whole-genome sequencing (WGS) to evaluate the pre- and post-digestion toxigenic potential, antimicrobial resistance profiles, and genetic diversity of MDR B. cereus strains isolated from food samples in Guangdong Province, China. The four B. cereus isolates investigated in this study exhibited a genetic diversity, as determined by multilocus sequence typing analysis of WGS data. All four isolates produced the diarrheal toxins Hbl, Nhe, and CytK to varying levels, indicative of their potential to cause outbreaks of foodborne diseases. Each of the four isolates exhibited resistance to more than three classes of antibiotics, fulfilling the criterion for multidrug resistance. At an initial concentration of 9 log colony-forming units (CFU)/mL, the intestinal concentration of these four isolates crossed the threshold required to induce widespread diarrhea in the general population. Under rice slurry protection, all tested isolates maintained intestinal concentration beyond the threshold when the initial concentration was increased to ≥8 log CFU/mL. Moreover, the upregulations of genes associated with acid tolerance, bile tolerance and stress response were observed in the surviving MDR B. cereus isolates. Digestion markedly altered the antibiotic resistance profiles of the MDR B. cereus isolates. In the absence of a food matrix, the MDR isolates lost their resistance to imipenem, meropenem, amoxicillin-clavulanic acid, and trimethoprim-sulfamethoxazole post-digestion and was influenced by the initial concentration of the strains. In the presence of food matrix rice slurry, the effects of digestion on the antibiotic resistance of MDR B. cereus isolates can be mitigated, enabling them to maintain their antibiotic resistance to the greatest extent. Most remarkably, after digestion, the isolates Bce055 and Bce166 exhibited newly emergent resistance to cefotetan and trimethoprim-sulfamethoxazole, respectively. Our findings clarify the fate of MDR B. cereus isolates in the gastrointestinal tract and inform the development of prevention and control strategies for foodborne diseases caused by this pathogen.

Drug Resistance, Multiple, Bacterial↗

PubMed1992

Nonspecific reactions of a commercial enzyme-linked immunosorbent assay kit (TECRA) for detection of staphylococcal enterotoxins in foods.

A staphylococcal enterotoxin visual immunoassay kit (TECRA) has recently become commercially available. Since the kit is an enzyme-linked immunosorbent assay system equipped with polyvalent antisera against staphylococcal enterotoxin types A to E (SEA to SEE) and the test is simple and rapid to perform (4 h), it has been widely used for screening purposes. In this study, the sensitivity of the kit for detection of SEA, SEB, and SEC in ham, cheese, and mushrooms was similar to those of kits based on an enzyme immunoassay and reversed passive latex agglutination: 0.75 to 1.0 ng of SEA per ml, 0.5 to 0.75 ng of SEB per ml, and 1.0 to 1.25 ng of SEC per ml. However, the TECRA kit showed nonspecific reactions with food samples contaminated by microorganisms other than Staphylococcus aureus, such as Enterobacter agglomerans, Enterobacter cloacae, Proteus mirabilis, Pseudomonas aeruginosa, and Serratia marcescens. The substance contributing to the false-positive results differed from true staphylococcal enterotoxins in that it was (i) heat labile (completely inactivated by heating for 2 min at 100 degrees C, whereas true staphylococcal enterotoxins were inactivated by about 10% with this treatment), (ii) lower in molecular weight than staphylococcal enterotoxins, and (iii) not bound to a copper chelate Sepharose gel (all of the substance remained in the unbound wash fraction, whereas staphylococcal enterotoxins were quantitatively bound to the gel). The problem of false-positive results with the TECRA kit could be resolved by heat treatment (2 min at 100 degrees C) or by cleanup procedures involving metal chelate affinity chromatography with copper chelate Sepharose for 4 h before use of the TECRA kit.

Enterotoxins↗