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PubMed1975

Evaluation of a selective medium for hydrogen sulfide production by salmonella.

An evaluation was made of Padron-Dock-Stader sulfide (PDS) agar for the rapid detection of Salmonella and Arizona microorganisms in foods. Analysts from 9 Food and Drug Administration District laboratories determined the reaction of 638 Salmonella cultures, 30 Arizona cultures, and 1754 non-Salmonella and non-Arizona cultures isolated from 157 food samples in PDS agar. The degree of positive reactions of these cultures in this agar was scored on a scale of "-" to "+++". The highest percentage of Salmonella isolates (64.1%) was in the category of +++ reactions. Progressively lower percentages of Salmonella isolates occurred in the more negative reaction categories. The highest percentage of Arizona isolates (66.7%) occurred in the intermediate ++ category. The majority of non-Salmonella and non-Arizona isolates occurred in the minus (41.0%) and plus or minus (44.8%) categories. Advantages of using the PDS agar are that it is simple to use, requires no specialized training or equipment, and alerts analysts to those Salmonella cultures which produce atypical reactions in triple sugar iron agar particularly the lactosepositive Salmonella. However, in this study the occurrence of false-negative reactions ranged from 4.3 to 13.9% for Salmonella and from 0 to 6.7% for Arizona, according to the criteria used to interpret the reactions in PDS agar.

Cells, Cultured↗

PubMed2002

Development of a technique to quantify the effectiveness of enrichment regimes in recovering "stressed" Listeria cells.

A rapid, reliable microwell plate method based on the most probable number (MPN) technique was used to determine the effectiveness of five enrichment regimes in the recovery and enumeration of Listeria spp. cells from five seafood products. The products tested were chosen to reflect conditions under which cells were exposed to the "stresses" associated with a variety of food-processing techniques, such as treatments involving an ethanol-based marinade, lowered pH (acetic acid), heat, sugar and salt brine (Gravilax), or frozen storage. Either Listeria monocytogenes and Listeria innocua were present in food samples as natural contaminants or L monocytogenes was added in the laboratory. Listeria repair broth (LRB), buffered Listeria enrichment broth, Listeria enrichment broth (LEB), Fraser broth, and University of Vermont modified Listeria enrichment broth were used to recover Listeria cells. The effectiveness of these enrichment regimes was found to be dependent on the type of stresses the cells had been exposed to. After exposure to ethanol, recovery of L monocytogenes cells was inhibited in enrichment regimes involving a nonselective period of resuscitation. On exposure to acetic acid, there were no significant differences (P < 0.05) between any of the regimes used. With heat-stressed cells, LRB recovered significantly fewer (P < 0.05) cells than did any other medium. On exposure to osmotic stress (elevated sugar and salt concentrations), LEB recovered the fewest cells. The largest number of cells was recovered from frozen fish (Hoki [Macruronus novazelandiae]) fillets with LRB. No single enrichment regime was consistently the most effective.

Animals↗

PubMed2003

Uranium concentration in typical Pakistani diet.

To strengthen the radiation protection infrastructure in Pakistan, the uranium concentration in daily diet was measured and its associated radiation risks were estimated for the adult population. Food samples were collected from major cities and districts of the country by the market basket method, from which daily diets were prepared. These diet samples were analyzed using inductively coupled plasma mass spectrometry (ICP-MS) at the National Institute of Radiological Sciences, Japan, the regional Central Reference Laboratory of the Reference Asian Man Project. The measured values of the uranium content were found to vary from 2.3 ng (g dry)(-1) to 11 ng (g dry)(-1). The geometric mean concentration and geometric standard deviation were 4.5 x//1.7 ng (g dry)(-1). This leads to a daily dietary intake of 2.6 x// 1.7 microg d(-1) or 33 x// 1.7 mBq d(-1), which is approximately 40% higher than the ICRP value. The measured value, i.e. 33 mBq d(-1), contributes 12 Bq y(-1) to annual intake of 238U activity and 0.54 microSv to the committed effective dose to the adult population. This is a very small fraction of the ICRP annual effective dose limit of 1 mSv for the general public. Therefore, it would pose no significant health hazard.

Diet↗

PubMed2006

Quantification of genetically modified soybeans using a combination of a capillary-type real-time PCR system and a plasmid reference standard.

Because the labeling of grains and feed- and foodstuffs is mandatory if the genetically modified organism (GMO) content exceeds a certain level of approved genetically modified varieties in many countries, there is a need for a rapid and useful method of GMO quantification in food samples. In this study, a rapid detection system was developed for Roundup Ready Soybean (RRS) quantification using a combination of a capillary-type real-time PCR system, a LightCycler real-time PCR system, and plasmid DNA as the reference standard. In addition, we showed for the first time that the plasmid and genomic DNA should be similar in the established detection system because the PCR efficiencies of using plasmid DNA and using genomic DNA were not significantly different. The conversion factor (Cf) to calculate RRS content (%) was further determined from the average value analyzed in three laboratories. The accuracy and reproducibility of this system for RRS quantification at a level of 5.0% were within a range from 4.46 to 5.07% for RRS content and within a range from 2.0% to 7.0% for the relative standard deviation (RSD) value, respectively. This system rapidly monitored the labeling system and had allowable levels of accuracy and precision.

Food, Genetically Modified↗

PubMed2006

A comparison of Listeria monocytogenes serovar 4b isolates of clinical and food origin in Austria by automated ribotyping and pulsed-field gel electrophoresis.

In this study, two typing methods, automated ribotyping and pulsed-field gel electrophoresis (PFGE), were evaluated for the subtyping of Listeria monocytogenes serotype 4b. The strains originated from patients and food samples collected in Austria during 2001-2005 and from Europe and North America in the World Health Organization collaborative study on the subtyping of this species. The largest group of Austrian clinical isolates was of the same PFGE subtype as those isolated from foodborne outbreaks in Switzerland and in the United States. Another subtype of clinical isolates from Austria was indistinguishable to that obtained from isolates responsible for a foodborne outbreak in the United States in 1985. Although the discriminatory power of PFGE was higher than that of automated ribotyping, some PFGE types were differentiated by ribotyping. Thus, combining data obtained by both automated ribotyping and PFGE increases the strain discrimination. Still, many of the Austrian strains remain indistinguishable from strains of foodborne outbreaks in other countries although there is no known epidemiological relation. This complies to previous studies which show the highly clonal nature of L. monocytogenes 4b strains which are responsible for both large outbreaks and sporadic cases.

Animals↗

PubMed2006

Biotyping of enterotoxigenic Staphylococcus aureus by enterotoxin gene cluster (egc) polymorphism and spa typing analyses.

Thirty-five Staphylococcus aureus strains, including 10 reference strains and 25 strains recovered from clinical specimens and food samples, were analyzed by PCR REA (restriction endonucleases analysis) of the egc operon and spa typing. Nineteen spa types and seven different egc operons, including four putative new egc variants, were revealed. In 13 strains, allelic variants of sei and/or seg were found. By an analysis of their nucleotide sequence identities, a new homogeneous cluster of a sei variant, called the sei variant, was detected in six strains. In addition, the prototype sei was shown to be more polymorphic than assumed so far. Seven strains possessed the recently described seg variant, also exhibiting several nucleotide exchanges. spa typing was more effective than REA egc grouping as a typing technique. Since, in some cases, the REA typing method was able to discriminate strains showing the same spa type, it must be considered for PCR approaches involved in diagnostic procedures and may be useful for epidemiological studies. Hence, the polyphasic approach used in this study can be reliably and advantageously applied for typing egc-positive S. aureus strains.

Alleles↗

PubMed2003

Isolation and molecular characterization of Escherichia coli O157 isolated from cattle, pigs and chickens at slaughter.

From 1999 until 2001, 3625 food samples were examined for the presence of Escherichia coli O157. Samples were from bovine origin (ground beef, n=549; carcasses, n=2452), calves (carcasses, n=147), chicken (breast, n=203; carcasses, n=71) and pigs (carcasses, n=85; trimmings, n=118). Vidas ECO detected 451 (12%) samples positive, but from only 27 (0.74%) samples was E. coli O157 isolated. One strain was isolated from bovine ground beef (0.18%), one from a pig carcass (1.17%) and all others were isolated from bovine carcasses (1.02%). All strains possessed the attaching-and-effacing gene, the enterohemorrhagic plasmid and verotoxin (VT) genes, except the strain isolated from the pig carcass that was therefore eliminated. Six of the strains were urease-positive. Strains were typed by two DNA fingerprinting methods: random amplification of polymorphic DNA (RAPD) and pulsed field gel electrophoresis (PFGE). PFGE revealed a similarity of 71.05%, while RAPD was 77.36% similar. None of the typing methods were able to classify all urease-positive strains to one pattern. Strains in the same PFGE cluster did not belong to one RAPD cluster. This paper highlights that Belgian fresh meat at retail level can be contaminated with E. coli O157 and that two different typing methods divide strains into different types.

Abattoirs↗

PubMed1993

Zinc, copper & iron contents in cooked foods & estimates of their daily intakes in young hostel residents.

Dietary zinc, copper and iron intakes of 19 men and 11 women (aged 18-25 yr) were determined during three periods of five consecutive days each, using, weighment method and atomic absorption analysis of food samples. Daily zinc, copper and iron intakes of men ranged from 13.1 +/- 1.2 to 15.3 +/- 1.4 mg/d, 1.62 +/- 0.15 to 1.84 +/- 0.17 mg/d and 20.5 +/- 2.8 to 29.1 +/- 4.5 mg/d and of women 8.8 +/- 2.0 to 9.0 +/- 1.6, 1.42 +/- 0.23 to 1.69 +/- 0.62, and 10.0 +/- 2.4 to 14.7 +/- 2.6 mg/d respectively. Cereals provided 67.7 per cent of dietary zinc, 47.7 per cent copper and 62 per cent iron in men and 60 per cent of Zn, 44 per cent of Cu and 59 per cent of Fe in women, suggesting lower contribution of cereals to Cu intakes than Zn and Fe. Men had mineral intakes close to the recommended allowances for Indians, whereas the intakes of women were 30 to 60 per cent lower. When expressed as mg/1000 kcal, lower calorie intakes of women were responsible for their low mineral intakes. Intra-individual variation in mineral intakes was higher (18.39%) than that of energy intakes (14-17%) in both men and women. Phytate: Zn molar ratios were > 15 indicating risk of zinc deficiency in these students.

Adolescent↗

PubMed1995

Development of a flow injection analysis (FIA) immunosensor for the detection of Escherichia coli.

A flow injection immunoanalysis (FIA) system has been developed for the detection of Escherichia coli in artificially contaminated food samples. Anti-E. coli antibodies were covalently immobilized onto porous aminopropyl glass beads via glutaraldehyde activation to form an immunoreactor. After adsorption of the cells onto anti-E. coli antibody bound glass beads, 4-methylumbelliferyl-beta-D-glucuronide was injected into the system which was then hydrolyzed by the adsorbed E. coli cells containing beta-D-glucuronidase, an enzyme which is very specific to E. coli and to a few other strains of Shigella. Fluorescent 4-methylumbelliferone released from the enzymatic reaction was then detected by a fluorometer. Owing to the specificity of the antibody towards E. coli, the FIA system was very selective for detection of E. coli whereas Shigella boydii, another GUD-positive bacterium, did not give any response. The FIA system was successfully used for detecting as low as 5 x 10(7) CFU/ml E. coli in less than 30 min and was reusable for at least 300 repeated assays. The immunoreactor yielded reproducible results during 3 months of experimentation if stored overnight at 4 degrees C in carrier buffer containing 0.05 to 0.25% Tween 20.

Escherichia coli↗

PubMed2000

A small outbreak of listeriosis potentially linked to the consumption of imitation crab meat.

A small outbreak of listeriosis involving two previously healthy adults occurred in Ontario. Food samples obtained from the refrigerator of the patients included imitation crab meat, canned black olives, macaroni and vegetable salad, spaghetti sauce with meatballs, mayonnaise and water. All of the samples except the water contained Listeria monocytogenes. The three most heavily contaminated samples were the imitation crab meat, the olives and the salad which contained 2.1 x 109, 1.1 x 107 and 1.3 x 106 cfu g-1, respectively. L. monocytogenes serotype 1/2b was isolated from the patients, as well as from the opened and unopened imitation crab meat. Molecular typing of the isolates by both randomly amplified polymorphic DNA (RAPD) and pulsed-field gel electrophoresis (PFGE) typing demonstrated the imitation crab meat and clinical strains to be indistinguishable. Challenge studies performed with a pool of L. monocytogenes strains showed that imitation crab meat, but not olives, supported growth of the organism. In this study we have shown for the first time the potential involvement of imitation crab meat in a small outbreak of listeriosis. In terms of disease prevention, temperature control is critical to prevent or reduce the growth of this foodborne pathogen. In addition, with refrigerated products having a long (> 30 d) shelf life, additional safety factors must be used to prevent the growth of foodborne pathogens such as L. monocytogenes.

Animals↗

PubMed1988

Trace mineral balance during acute diarrhea in infants.

To evaluate the magnitude of copper and zinc losses during acute diarrhea requiring hospitalization, we studied 14 infants, 3 to 14 months of age, and compared them with a control group of 15 infants of similar age, birth weight, and nutritional status. Metabolic balance studies were conducted in the study group during an initial 48 hours (period 1) and on days 6 and 7 after admission (period 2). The control group was studied after recovery from respiratory disease. Copper and zinc content of feces, urine, and food samples was measured by atomic absorption spectrophotometry. Mean (+/- SD) fecal losses were higher for period 1 in the diarrhea group than in control subjects: Cu 55.7 +/- 21.2 versus 28.8 +/- 6.7 micrograms/kg/body weight/day (p less than 0.01); Zn 159.4 +/- 59.9 versus 47.4 +/- 6.4 micrograms/kg/day (p less than 0.0001). For period 2, Zn losses were similar in both groups, but Cu balance remained negative only in the study group. Retention of Zn for the study group went from -21.2 +/- 46.7 in period 1 to 204.5 +/- 103.0 micrograms/kg/day in period 2 (p less than 0.0001), and fecal weight decreased from 70.5 +/- 20.6 in period 1 to 36.8 +/- 20.0 gm/kg/day in period 2. Fecal weight and fecal losses were correlated: r = 0.71 (p less than 0.01) for Cu and r = 0.81 (p less than 0.001) for Zn. Plasma mean Cu and Zn levels were low in period 1 but rose in period 2, especially for Zn. A negative correlation was found between fecal Zn losses and plasma Zn: r = 0.74 (p less than 0.001). We conclude that acute diarrhea leads to Cu and Zn depletion and that plasma levels and Cu balance remain abnormal a week after admission.

Copper↗

PubMed2002

Detection of bacteria using foreign DNA: the development of a bacteriophage reagent for Salmonella.

A phage-based reagent was developed for the detection of Salmonella in food samples. The parental phage was Felix 01, which lyses practically all Salmonella. Using data obtained about the molecular biology of the phage, a recombinant phage that carried the bacterial genes specifying luciferase was produced. The method involved the isolation of amber nonsense mutations and subsequent crosses to render doubly mutant phage with a very low reversion rate on strains lacking an amber suppressor. A plasmid was constructed that contained a segment of Felix 01 DNA with two adjacent genes, one dispensable and the other essential, and their flanking sequences. Recombinant DNA technology was used to remove the two genes and the luxA and luxB genes for luciferase, and a gene specifying a tRNA that recognizes amber codons (supF=tyrT) was put in their stead. This region could be transferred into the genome of the phage by homologous recombination. The recombinant phage cannot grow because it lacks an essential gene. However, it can grow in a host that synthesizes the missing protein. This technique allows the construction of "locked" recombinant phages that carry foreign DNA but which cannot propagate themselves in nature.

DNA Transposable Elements↗

PubMed2006

[Application of pulsed-field gel electrophoresis typing in tracing and carrying out surveillance programs on O139 cholera outbreaks].

OBJECTIVE: To study the characteristics of molecular typing and phylogenic relationship among the Vibrio cholerae serogroup O139 strains isolated from environment and sea food samples during cholera outbreaks, in Sichuan province in 2004 and to trace the source of infections so as to support the ascertainment of epidemic control strategy. METHODS: Cholera toxin gene was detected by polymerase chain reaction amplification. Pulsed-field gel electrophoresis (PFGE) was used for subtyping of isolates and clustering of patterns was analysed with the software BioNumerics. RESULTS: In all the 72 strains under analysis, 68 appeared to be toxigenic while 4 from river water derived isolates were toxin gene negative. Sixty-seven strains were clustered into 16 PFGE patterns when digested with Not I. The patterns of toxigeinc O139 strains isolated from turtles in the markets were identical with the patterns of strains appeared in the outbreaks respectively. The PFGE patterns of isolates from different outbreaks were inconsistent. CONCLUSION: The sources of infection causing these outbreaks were complicated. Contaminated turtles might also be one of the major sources of outbreaks when being served at the dinner parties in Sichuan in 2004.

Animals↗

PubMed2001

Degradation of tetrahydro-beta-carbolines in the presence of nitrite: HPLC-MS analysis of the reaction products.

Motivated by the identification of numerous novel tetrahydro-beta-carboline-carboxylic acids in food samples, we studied the reactions of tetrahydro-beta-carbolines in the presence of nitrosating agents. The anticipated formation of nitroso derivatives from unsubstituted tetrahydro-beta-carbolines, and from tetrahydro-beta-carboline-3-carboxylic acids was indicated by HPLC-MS/MS analysis and validated by the characteristic product ion spectra of the respective nitroso compounds. In addition, oxidative decarboxylation resulted in formation of the corresponding dihydro-beta-carbolines, and in the generation of the beta-carbolines harman or norharman. Subsequently, we studied the reactivity of tetrahydro-beta-carboline-1-carboxylic acids derived from the Pictet-Spengler condensation of indole amines with alpha-oxo acids. Again, in the presence of nitrosating agents the rapid disappearance of the starting material was obvious, but no nitroso derivatives could be observed. Instead, further HPLC-MS/MS studies demonstrated that dihydro-beta-carbolines were the major products of tetrahydro-beta-carboline-1-carboxylic acids. Finally, we demonstrated that freshly isolated nitroso-precursors spontaneously decomposed to yield harman alkaloids. In conclusion, we revealed that nitroso-tetrahydro-beta-carbolines can represent intermediates involved in the generation of beta-carbolines, and we established a novel pathway for the formation of harman alkaloids from nutritional tetrahydro-beta-carbolines.

Carbolines↗

PubMed1999

Exposure of cadmium from infant formulas and weaning foods.

Cadmium levels were determined in 59 baby food samples, including milk-based, cereal and milk-based and soy-based formulas, recommended from 0 to 18 months of age. Determinations were performed by Zeeman graphite furnace atomic absorption spectrophotometry, after dry ashing, with parallel determinations of certified reference samples. Mean cadmium levels were found to range from 1.10 to 23.5 micrograms/kg fresh weight concentrated formulas. Levels were related to the composition of the diets. Formulas based on cow's milk had the lowest concentrations. Soy formulas contained approximately six times more cadmium than cow's milk formulas, and diets with a cereal content had 4-21 times higher mean levels. The mean weekly intakes of dietary cadmium were estimated to vary between 0.10 and 3.05 micrograms/kg body weight of the child, if the recommended amount of formula were to be consumed at the recommended age, and if the child were of average weight. This estimation however does not include the contribution of cadmium from drinking water. The highest intake on a body weight basis was found in 6-month-old children, consuming the recommended amount of wheat-, oat- and milk-based formulas. This intake is below the provisional tolerable weekly intake (PTWI) of 7 micrograms/kg body weight, established by a WHO/FAO expert group. However, the risk assessment is based on renal effects in adults. Furthermore, preparations of a formula by adding water with cadmium concentrations at the WHO guideline level could lead to intakes at the PTWI level. Compared to breast-fed children, the exposure of dietary cadmium from weaning diets can be up to 12 times higher in children fed infant formula.

Cadmium↗

PubMed2004

Development and in-house validation of a liquid chromatography-electrospray-tandem mass spectrometry method for the simultaneous determination of Sudan I, Sudan II, Sudan III and Sudan IV in hot chilli products.

An accurate method based on the use of reversed-phase (RP) liquid chromatography-tandem mass spectrometry interfaced with electrospray (LC-ESI-MS/MS) was devised for the determination of Sudan I, Sudan II, Sudan III and Sudan IV in hot chilli food samples. A simple sample treatment procedure entailing the use of an extraction step with acetone without clean-up was developed. A C18 column with an aqueous formic acid/methanol mixture as the mobile phase was used under isocratic conditions. Mass spectral acquisition was done in positive ion mode by applying selected reaction monitoring of three fragmentation transitions per compound to provide a high degree of selectivity. The method was in-house validated in terms of detection limits (LOD), quantitation limits (LOQ), linearity, sensitivity, accuracy, recovery, and selectivity on two kinds of hot chilli sauces. Good results in the low ng/g level were obtained for LOD and LOQ of all analytes in matrices. Under both intra-day repeatability (R.S.D. between 1 and 13%) and intermediate precision (about 5-15% R.S.D. for both chilli sauce matrices) conditions, precision proved to be typical of determinations based on electrospray LC-MS and acceptable for routine monitoring purposes. Extraction recoveries for all four azo-dyes in chilli tomato sauce ranged from 92 to 103% at a spiking level of 5 microg/kg, whereas values between 72 and 97% were calculated in chilli tomato and cheese sauce at the same concentration level. The applicability of the method to the determination of Sudan azo-dyes in hot chilli products was demonstrated.

Azo Compounds↗

PubMed2005

Evolution and molecular phylogeny of Listeria monocytogenes isolated from human and animal listeriosis cases and foods.

To probe the evolution and phylogeny of Listeria monocytogenes from defined host species and environments, L. monocytogenes isolates from human (n = 60) and animal (n = 30) listeriosis cases and food samples (n = 30) were randomly selected from a larger collection of isolates (n = 354) obtained in New York State between 1999 and 2001. Partial sequencing of four housekeeping genes (gap, prs, purM, and ribC), one stress response gene (sigB), and two virulence genes (actA and inlA) revealed between 11 (gap) and 33 (inlA) allelic types as well as 52 sequence types (unique combination of allelic types). actA, ribC, and purM demonstrated the highest levels of nucleotide diversity (pi > 0.05). actA and inlA as well as prs and the hypervariable housekeeping genes ribC and purM showed evidence of horizontal gene transfer and recombination. actA and inlA also showed evidence of positive selection at specific amino acid sites. Maximum likelihood phylogenies for all seven genes confirmed that L. monocytogenes contains two deeply separated evolutionary lineages. Lineage I was found to be highly clonal, while lineage II showed greater diversity and evidence of horizontal gene transfer. Allelic types were exclusive to lineages, except for a single gap allele, and nucleotide distance within lineages was much lower than that between lineages, suggesting that genetic exchange between lineages is rare. Our data show that (i) L. monocytogenes is a highly diverse species with at least two distinct phylogenetic lineages differing in their evolutionary history and population structure and (ii) horizontal gene transfer as well as positive selection contributed to the evolution of L. monocytogenes.

Animal Feed↗

PubMed2006

Antimicrobial resistance in nontyphoidal Salmonella from food sources in Colombia: evidence for an unusual plasmid-localized class 1 integron in serotypes Typhimurium and Anatum.

Seventy-two isolates representing 18 serotypes recovered from various food samples collected in Colombia were tested for antimicrobial susceptibilities. The collection was further characterized for extended-spectrum cephalosporin, aminoglycoside, and tetracycline resistance markers. Multidrug resistant (MDR) isolates were further investigated for class 1 integrons and were evaluated for the presence of conjugative plasmids along with a determination of the incompatibility group by polymerase chain reaction (PCR). Antibiogram analysis showed that the incidence rate of ceftiofur resistance was moderately high (15%). A similar level of resistance to neomycin and oxytetracycline (11% and 10%, respectively) was also observed. There was a high prevalence of gene cassettes as part of one or more class 1 integrons (61%), many of which contained determinants that contributed to the resistance profile. Class 1 integrons identified in MDR Salmonella enterica serotypes Typhimurium and Anatum isolates were characterized. Sequencing identified several incomplete open reading frames (ORFs) as part of a gene cassette (bla-( imp-13 ), dfr7, blr1088, and aac8) along with a complete gene cassette (bla-(oxa2)) in each case. A mosaic of gene cassettes was identical in the two Salmonella serotypes. These integrons were located to a conjugative replicon. Plasmid profiling and incompatibility typing identified three plasmids belonging to Inc groups A/C, P, and W. Our study highlights the role of integrons, contributing to a MDR phenotype that is capable of dissemination to other bacteria.

Anti-Bacterial Agents↗