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PubMed1983

Antimicrobial resistance of gram-negative bacteria isolated from foods in Mexico.

When trimethoprim-sulfamethoxazole was given to US travelers in Mexico to prevent diarrheal illness, high-level resistance to the drug emerged [2], although in previous studies such resistance had not been observed among enteric flora following administration of trimethoprim-sulfamethoxazole as prophylaxis against urinary tract infection [3]. Since food has been shown to be an important vehicle of transmission of travelers' diarrhea, food samples were examined for the presence of drug-resistant bacteria to explain the acquisition of high-level resistance among enteric flora of individuals taking antibiotics as prophylaxis against traveler's diarrhea. Of 34 strains of ETEC isolated from US students in Guadalajara, Mexico, who had acute gastroenteritis, one was resistant to trimethoprim and one was resistant to trimethoprim-sulfamethoxazole. Eight of the ETEC strains tested demonstrated multiple drug resistance. Twenty-two of 149 isolates from food produced enterotoxin. Only one isolate, which was nontoxigenic, was resistant to trimethoprim, and no coliforms were resistant to trimethoprim-sulfamethoxazole; however, 16 isolates demonstrated multiple drug resistance. Of 235 gram-negative organisms recovered from frozen food samples grown on antibiotic-containing media and tested for enterotoxin production, no isolates were enterotoxigenic. Thirty-four isolates were resistant to trimethoprim, 15 were resistant to trimethoprim-sulfamethoxazole, and 33 demonstrated multiple resistance. Multiple drug resistance was demonstrated among gram-negative organisms isolated from patients' stools and foods in Mexico.(ABSTRACT TRUNCATED AT 250 WORDS)

Anti-Bacterial Agents↗

PubMed2005

Application of real-time PCR for quantitative detection of Clostridium botulinum type A toxin gene in food.

The TaqMan real-time PCR method for the quantitative detection of C. botulinum type A was developed based on sequence-specific hybridization probes. The validity of this assay was verified by using 10 genera of 20 strains, including reference strains of C. botulinum types A, B, C, D, E and F. The detection limit of this assay was evaluated on C. botulinum type A, using a 10-fold dilution series of DNA and spores . The DNA and spores were detected up to level of 0.1 ng/ml and 10(2)spores/ml, respectively. Spore spiked food sample preparation prior to the real-time PCR was performed by two methods, heat treatment and GuSCN. The detection limits after heat treatment showed 10(2) spores/ml for spiked sausage slurry, and 10(3) spores/ml for spiked canned corn slurry, while detection limits after GuSCN precipitation showed 10(2) spores/ml in both sausage and canned corn. Therefore the real-time PCR assay after GuSCN precipitation is useful for the quantification of C. botulinum type A because it showed identical CT values in both pure spore solutions and food slurries. We suggest that quantitative analysis of C. botulinum type A by TaqMan real-time PCR can be a rapid and accurate assessment method for botulinal risk in food samples.

Botulinum Toxins, Type A↗

PubMed2002

Comparison of LST + MUG broth technique and conventional method for the enumeration of Escherichia coli in foods.

AIMS: To reduce the analysis time needed for the enumeration of Escherichia coli, a rapid fluorogenic method (MUG) which takes only 48 h was compared with the standard most probable number (MPN) method which takes 6 days as described in the International Standards Organization (ISO). This study provides reliability data for the fluorogenic method applied to certain foods. METHODS AND RESULTS: Both methods were applied to 500 food samples which were analysed for E. coli enumeration. Agreement between the two methods was found in 409 (81 x 8%) samples; 81 (16 x 2%) samples gave higher values by the fluorogenic method, and only 10 (2 x 0%) samples were more effectively assayed by the ISO method. According to statistical analysis, the reliability between the methods was r = 0 x 9706, r(2) = 0 x 9421 and Cronbach's alpha = 0 x 9851. While all three values showed a high degree of correlation (P < 0 x 0001) between the two methods, McNemar's test demonstrated a significant difference between them, indicating that the MUG method was more reliable than the ISO method. CONCLUSIONS: The data suggest that the fluorogenic method is more reliable and shorter to perform than the standard ISO method. SIGNIFICANCE AND IMPACT OF THE STUDY: Comparison of the two methods may provide a rapid and more reliable alternative for the enumeration of E. coli in food samples.

Bacteriological Techniques↗

PubMed2000

Pesticide residues in the Canadian Market Basket Survey--1992 to 1996.

Market basket food samples from six Canadian cities collected from 1992 to 1996 were analysed for pesticide residues. One hundred and thirty-six composites were prepared for each city, representing 99% of the Canadian diet. Residues were found most frequently in peanut butter and butter. DDE, malathion and captan occurred most frequently, while the fungicides chlorothalonil, dicloran and captan were present in the highest concentrations. Processed commodities contained fewer residues and at lower concentrations than the raw products. No residues were detected in either milk or soy-based infant formula. Of the infant foods sampled, fruit contained both the greatest number and highest concentrations of pesticides.

Arachis↗

PubMed1995

Media for Aeromonas spp., Plesiomonas shigelloides and Pseudomonas spp. from food and environment.

Several media are proposed particularly for the detection of Aeromonas spp. but also for Plesiomonas shigelloides and Pseudomonas spp. Some are for general purposes and others specifically for the examination of clinical, environmental or food samples. All media are selective, due to antibiotics, bile salts, dyes and other selective agents, as well as differential, primarily based on the ability of the microorganisms to ferment/not ferment carbohydrates. As with all selective media, the recovery of stressed cells is sometimes prevented and the competing flora is not always completely inhibited so that confirmatory tests need to be made on presumptive positive colonies. The choice of a specific medium for isolation of Aeromonas spp. will always depend on the type of sample to be examined and whether the investigator needs qualitative detection or quantitative recovery. The best medium for quantitative estimation of Aeromonas spp. from food and environmental samples seems to be starch ampicillin agar (SAA), though others might be recommended. There is a need for a comparative study including Rippey Cabelli agar (mA), ampicillin bile salts inositol xylose (MIX) agar, ampicillin dextrin agar (ADA), dextrin fuchsin sulphite agar (DFS) and starch glutamate ampicillin penicillin C-glucose agar (SGAP-10C) in addition to SAA. For routine analysis of environmental and food samples for P. shigelloides, spread plating on inositol brilliant green bile salts (IBB) and plesiomonas (PL) agars is recommended. For Pseudomonas spp., CFC agar permits quantitative recovery of both pigmented and non-pigmented strains from food and environmental samples, whilst at the same time inhibiting most other organisms.

Aeromonas↗

PubMed1991

Use of probes to detect virulence factor DNA sequences in Escherichia coli strains isolated from foods.

Escherichia coli strains were isolated from 96 food samples (32 milks, 4 dairy products, 36 raw meats, 7 meat products, 7 sandwiches and 10 ready-to-eat meals). A total of 306 colonies was submitted to hybridization assays with DNA probes for the following virulence factors: heat-labile toxins (LT-I and LT-II), heat-stable toxins (ST-h and ST-p). Shiga-like toxins (SLT-I and SLT-II), adherence factor of enteropathogenic E. coli (EAF) and invasive factor (INV). Six colonies isolated from 4 food samples hybridized with the probes for LT-II (3 colonies isolated from a milk sample), SLT-I and SLT-II (1 colony isolated from raw bovine meat) or EAF (2 colonies isolated from two raw chicken meat samples).

Adhesins, Escherichia coli↗

PubMed2002

[Development of a rapid separating incubation method for detection of Escherichia coli O157:H7 in food].

To detect Escherichia coli O157:H7 in food, a selective and differential medium, CTV-MUG-RSMAC agar, was designed. Using this medium, the growth of most interfering organisms could be inhibited, and three main biochemical characteristics, including sorbitol-negative, rahmnose-negative and MUG-negative, to identify E. coli O157:H7 could also be simultaneously recognized. Sorbitol-positive aberrance strains of E. coli O157:H7 could be distinguished on the medium. The procedure of detecting food sample includes adding sample to selective broth and incubating overnight at 42 degrees C, streaking the inoculum to CTV-MUG-RSMAC agar and incubating at 37 degrees C for 24 h, and picking the typical colonies to react with sera for O157 and H7 antigens, and then take biochemical tests. The procedure could be finished within 3 days. This method has been applied to 126 food samples, and E. coli O157:H7 was detected from 3 samples. The results were in coincidence with those using FDA method.

Animals↗

PubMed1995

Polymerase chain reaction (PCR) for detection of pathogenic microorganisms in bacteriological monitoring of dairy products.

The presence of pathogenic bacteria poses a serious problem in sustaining the safety of dairy products. Microbiological routine controls of these products make use of selective culture techniques. To detect pathogenic species, isolated colonies are characterized by specific metabolic activities and by serotyping. We present an alternative biochemical approach that does not require culture of bacteria. The total bacterial populations of food samples were isolated by centrifugation and analysed by PCRs specific for pathogenic species. A total of 90 raw milk samples and dairy products made from raw milk were screened by this method for the presence of Listeria monocytogenes, Escherichia coli, enterotoxigenic E. coli, Campylobacter jejuni and C. coli. Detection rates were 12/90 (13%) for L. monocytogenes, 41/90 (46%) for E. coli, 18/90 (20%) for enterotoxigenic E. coli producing heat-labile toxin type I or heat-stable toxin type I, and 6/90 (7%) for C. jejuni or C. coli. Except for the use of different amplification primers, this approach is identical for any bacterial species to be detected. Direct PCR analysis of food samples offers rapid screening for the presence of specific bacteria and enables selection of critical samples prior to culture.

Animals↗

PubMed2002

Determining dioxin-like compounds in selected Korean food.

To measure the levels of dioxin-like compounds, pork, mackerel, cheese and milk were analyzed. The food samples were obtained at three different markets in Seoul. All the samples were animal origin and their lipid contents ranged from 4% to 34%. After extraction, extracts were cleaned up by sulfuric acid impregnated silica gel, purified on a series of silica gel, alumina, carbon column chromatography and then analyzed by high resolution gas chromatography/high resolution mass spectrometry. The levels of polychlorinated dibenzo-p-dioxins/furans for pork, mackerel, cheese and milk were 0.0008, 0.8663, 0.002 and 0.0236 pgTEQ/g wet weight, respectively. In addition, the levels of non-ortho coplanar polychlorinated biphenyls for pork, mackerel, cheese and milk were 0.0041, 1.5781, 0.0259 and 0.0353 pgTEQ/g wet weight, respectively. Among food samples analyzed, pork showed the lowest level of dioxin-like compounds.

Animals↗

PubMed2001

Putative virulence factor expression by clinical and food isolates of Bacillus spp. after growth in reconstituted infant milk formulae.

Forty-seven strains representing 14 different Bacillus species isolated from clinical and food samples were grown in reconstituted infant milk formulae (IMF) and subsequently assessed for adherence to, invasion of, and cytotoxicity toward HEp-2 and Caco-2 cells. Cell-free supernatant fluids from 38 strains (81%) were shown to be cytotoxic, 43 strains (91%) adhered to the test cell lines, and 23 strains (49%) demonstrated various levels of invasion. Of the 21 Bacillus cereus strains examined, 5 (24%) were invasive. A larger percentage of clinically derived Bacillus species (20%) than of similar species tested from the food environment were invasive. Increased invasion occurred after growth of selected Bacillus species in reconstituted IMF containing glucose. While PCR primer studies revealed that many different Bacillus species contained DNA sequences encoding the hemolysin BL (HBL) enterotoxin complex and B. cereus enterotoxin T, not all of these isolates expressed these diarrheagenic genes after growth in reconstituted IMF. Of the 47 Bacillus isolates examined, 3 isolates of B. cereus and 1 isolate of B. subtilis produced the HBL enterotoxin after 18 h of growth in brain heart infusion broth. However, eight isolates belonging to the species B. cereus, B. licheniformis, B. circulans, and B. megaterium were found to produce this enterotoxin after growth in reconstituted IMF when assessed with the B. cereus enterotoxin (diarrheal type) reversed passive latex agglutination (RPLA) kit. It is concluded that several Bacillus species occurring occasionally in clinical specimens and food samples are of potential medical significance due to the expression of putative virulence factors.

Animals↗

PubMed1993

Determination of nanogram amounts of iodine in foods by radiochemical neutron activation analysis.

Three different neutron activation analysis methods have been developed for the determination of ppb levels of iodine in food samples. The methods are based on the separation of iodine using (i) toluene extraction followed by bismuth sulfide coprecipitation; (ii) bismuth sulfide coprecipitation followed by radiochemical purification with palladium iodide; and (iii) radiochemical isolation by bismuth sulfide coprecipitation. The accuracy of these methods was evaluated by analysing replicate samples of reference materials. The measured values of iodine in A-11 Milk Powder, H-4 Animal Muscle and H-9 Mixed Human Diet from the International Atomic Energy Agency (IAEA) are statistically indistinguishable from the IAEA recommended values, and those for the Standard Reference Materials 1571 Orchard Leaves and 1577 Bovine Liver from the National Institute of Standards and Technology (NIST) are in good agreement with the NIST information values. The precision, in terms of relative standard deviation, is 5% at 50-100 ppb and 10% at 5-20 ppb levels of iodine. The absolute detection limits of these methods vary between 0.5 and 10 ng of iodine. All three methods were used to measure the iodine content of several food samples. The method involving bismuth sulfide coprecipitation followed by radiochemical purification provides the best detection limit and highest precision.

Food Analysis↗

PubMedDate not supplied

Determination of ethylene dibromide in foods and grains by high resolution capillary gas chromatography with electron capture detection.

Ethylene dibromide (EDB) levels in food samples were determined by gas chromatography with a high-resolution capillary column and electron capture detector. The capillary column used was 3 mm id X 25 m cross-linked 5% phenylmethyl silicone. Column temperature was set at 40 degrees C by a coolant containing carbon dioxide gas. Optimum temperatures of the injection port and detector were 200 and 350 degrees C, respectively. The detection limit was 0.5 ppb and linear from 1 to 20 pg on the dynamic range. EDB residues in food samples were extracted with n-hexane by steam distillation. A few impurity peaks appeared near EDB on the chromatogram; however, the EDB peak was resolved. Recoveries of EDB from wheat and brown rice ranged from 66.1 to 99.6%. EDB was detected in 3 samples of imported wheat at a range of 0.74-1.70 ppb, and was not detected at all in 37 samples. The EDB remaining in EDB-fortified cookies after baking was examined. The amounts of EDB were reduced to 30 to 50% of the original amounts by kneading the dough, and to below 1.5% by baking.

Chromatography, Gas↗

PubMedDate not supplied

Gamma-ray spectroscopic determination of iodine-131 and cesium-137 in foods: two collaborative studies.

The AOAC method for iodine-131, cesium-137, and barium-140 in milk by gamma-ray spectroscopy (48.025-48.029) was extended to include other foods for the radionuclides iodine-131 and cesium-137. Two collaborative studies were performed to validate this extension. In the first study, a food sample containing 119 pCi 131I/kg and 53 pCi 137Cs/kg was sent to each of 45 laboratories for triplicate analyses. For 25 responses, the mean of the reported values was 123.8 pCi/kg for iodine-131, and for 27 responses, the mean was 53.4 pCi/kg for cesium-137. Repeatability (within-laboratory) standard deviations (Sr) for iodine-131 and cesium-137 were 4.6 and 3.7 pCi/kg, respectively. Reproducibility (among-laboratories) standard deviations (SR) for iodine-131 and cesium-137 were 12.1 and 6.0 pCi/kg, respectively. In the second study, a food sample containing 25 pCi 131I/kg and 27 pCi 137Cs/kg was sent to each of 54 laboratories for triplicate analyses. For 21 responses, the mean of the reported values was 25.0 pCi/kg for iodine-131, and for 19 responses, the mean was 28.9 pCi/kg for cesium-137. Sr Values were 4.0 and 1.6 pCi/kg for iodine-131 and cesium-137, respectively, and SR values were 5.0 and 2.8 pCi/kg, respectively. The method extension was adopted official first action.

Animals↗

PubMed1992

Isolation of salmonellas by immunomagnetic separation.

Magnetisable particles, coated with anti-salmonella serum, were used to isolate Salmonella livingstone from pure cultures, mixed cultures and food samples. Beads (10(7] were generally incubated with 10(4) 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 51.0 +/- 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 Salm. 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.

Culture Media↗

PubMed2004

The usefulness of molecular techniques to assess the presence of Aeromonas spp. harboring virulence markers in foods.

A total of 78 raw and 123 processed and ready-to-eat retail food samples were used to assess the presence of motile Aeromonas spp. harboring virulence genes (cytotoxic enterotoxin and hemolysin genes) using a recently described PCR method in comparison with the conventional cultivation method based on the use of Ampicillin-Dextrin Agar (ADA) medium. With the ADA-based method, 65/201 (32.3%) samples showed presumptive Aeromonas spp. colonies whereas the PCR method revealed the presence of Aeromonas spp. harboring the targeted virulence genes in 51/201 (25.4%) of the tested samples. The rate of contaminated samples and the presence of pathogenic Aeromonas were significantly lower with both methods for processed than in case of raw samples. A polyphasic identification approach including biochemical and molecular techniques was applied to a selection of 34 PCR-positive presumptive Aeromonas isolates. Following fatty acid methyl ester (FAME) analysis and amplified fragment length polymorphism (AFLP) fingerprinting, a total of 33 isolates (97%) could be identified to the DNA hybridization group (HG) level. The majority of these isolates belonged to the species Aeromonas hydrophila HG3 (50%) and Aeromonas veronii biovar sobria (HG8/10) (38%). Molecular characterization of PCR amplicons obtained from these strains by PCR-Restriction Fragment Length Polymorphism (PCR-RFLP) fingerprinting and PCR-Amplicon Sequence Analysis (PCR-ASA) allowed classification of all strains in a known PCR-RFLP and PCR-ASA type. In conclusion, the current findings demonstrate that the combined use of PCR-based virulence marker detection, PCR-RFLP and PCR-ASA offers a rapid, sensitive, and specific system to assess the presence and prevalence of Aeromonas spp. harboring virulence markers in food samples.

Aeromonas↗

PubMed1999

A nursing home outbreak of Clostridium perfringens associated with pureed food.

OBJECTIVE: To investigate and ascertain the source of a nursing home outbreak of gastroenteritis in Melbourne in 1997. METHOD: A retrospective cohort study. We obtained fecal and food samples and environmental swabs, and reviewed food handling. RESULTS: There were 25 cases, and 21 of these had their meals pureed (liquidised). The relative risk for eating pureed food and becoming ill was 5.8 (95% CI 2.2-15.4). Clostridium perfringens and its enterotoxin was detected in nine fecal samples. Samples of pureed food tested positive for coliforms. CONCLUSIONS: This outbreak was caused by C. perfringens contaminating pureed food. Food liquidising provides opportunities for re-contamination of cooked food through the use of contaminated equipment and deficiencies in food handling practices. Pureed foods should be reheated to 70 degrees C after liquidising to inactivate pathogens. IMPLICATIONS: Health care facilities need to take specific precautions to manage the special hazards involved in preparing pureed food.

Aged↗

PubMed1982

Mutagenicity of various Japanese foodstuffs treated with nitrite.

Mutagenic activities of various Japanese foodstuffs treated with nitrite at pH 4.2 for 10 min (37 degrees C) were tested using Salmonella typhimurium TA 100, TA 1535 and also a streptomycin(SM)-dependent strain of Salmonella typhimurium TA 100. Among 46 common food samples tested, smoked ham, red wines, black teas, soybean pastes and instant coffee powder gave greatly increased numbers of His+ revertants or SM-independent colonies when treated with nitrite. Vegetables, soybean-seasonings and a variety of broths developed no significant mutagenic potential when treated with nitrite. Broiled fish, such as broiled mackerel pike, jack mackerel, tuna and sardine, gave a very slight increase, or often a decrease, in numbers of mutant colonies when treated with nitrite. In order to explore the substances responsible for the development of mutagenic activities in nitrite-treated foodstuffs, several nitrosatable compounds, including polyamines, were investigated. Polyamines are known to react with nitrite to produce several direct-acting mutagens in a short incubation time. Food samples were hydrolyzed with 6 mol/l hydrochloric acid, followed by purification using Amberlite CG-120, and were then submitted to GC analysis, after ethyloxycarbonylation. The high concentration of polyamines which was found in soybean paste could, to some extent, be correlated to the large increase of the mutagenic activities in the foodstuffs treated with nitrite.

Food Additives↗

PubMed2002

Detection of Escherichia coli O157:H7 in raw meat by immunomagnetic separation and multiplex PCR.

The aim of this research was to elaborate fast and sensitive method ofdetection of E. coli O157:H7 in food samples. Raw ground meat obtained from retail was artificially inoculated with low numbers of E. coli O157:H7. 18 h enrichment culture allowed pathogenic bacteria to multiply to the levels detectable in multiplex PCR. Immunomagnetic separation with magnetic beads coated with an antibody against E. coli O157:H7 were used to concentrate target bacteria and to separate PCR inhibitors. A portion of the bacterial suspension was used in a multiplex PCR to amplify eae (attaching and effacing) gene, stx (shiga toxin) genes and 90 kbp plasmid. The sensitivity of E. coli O157:H7 detection method was shown to be 1 cfu per 25 g of food sample. The total analysis can be completed within 24 h, whilst traditional methods involves enrichment, direct plating and confirmation tests with entire time at least 3 days.

Animals↗