scholarly journals A comparison of confirmatory media for coliform organisms and Escherichia coli in water

1981 ◽  
Vol 87 (3) ◽  
pp. 369-375 ◽  
Keyword(s):  
Escherichia Coli ◽  
Brilliant Green ◽  
False Negative ◽  
Gas Production ◽  
Single Tube ◽  
Negative Results ◽  
False Negative Results ◽  
Indole Production

SummaryGas production by coliform organisms and Escherichia coli from lauryl tryptose lactose broth (LTLB) was compared with that from brilliant green (lactose) bile broth (BGB). These media were compared with lauryl tryptose mannitol broth (LTMB) with and without added tryptophan for both gas and indole production. At 37 °C, LTLB and BGB were both satisfactory for gas production, but at 44 °C, LTLB gave fewer false-negative results and was thus significantly less inhibitory than BGB. However when LTLB and LTMB were compared as single-tube confirmatory media, LTLB give a high proportion of false-negative reactions in the indole test at 44 °C. The substitution of mannitol for lactose and the addition of tryptophan yielded a satisfactory medium for both confirmation of gas production and the demonstration of indole at 44 °C.

Preenrichment Conditions for Effective Recovery of Salmonella in Foods and Feed Ingredients

1979 ◽  
Vol 42 (2) ◽  
pp. 153-157 ◽  
Author(s):  
J. Y. D'AOUST ◽  
C. MAISHMENT
Keyword(s):  
Brilliant Green ◽  
False Negative ◽  
Food Samples ◽  
Contamination Level ◽  
Experimental Conditions ◽  
Feed Ingredients ◽  
Selective Enrichment ◽  
Negative Results ◽  
False Negative Results ◽  
The Cost

The efficacy of Clausen, EE, Eugon, GN, Tergitol 7, lactose and nutrient broths as Salmonella preenrichment media was evaluated using 165 food samples with an incident contamination level ranging from 1.5 to 460 salmonellae/100 g. Replicate food samples (100 g) were preenriched in each of seven media (900 ml) for 6 h and 24 h at 35 C; various amounts (10, 1.0 and 0.1 ml) of preenriched cultures were selectively enriched in tetrathionate brilliant green (43 C) and selenite cystine (35 C) broths and plated on bismuth sulfite and brilliant green sulfa agars. Short (6 h) and 24-h preenrichment conditions resulted in 26 (16%) and 8 (5%) false negative results, respectively. Recovery of Salmonella from 6-h but not 24-h preenrichment cultures also varied directly with the portion of culture inoculated into selective enrichment broths. None of the preenrichment media tested performed satisfactorily at 6 h of incubation where levels of recovery ranged from 32 to 62%; at 24 h, good recovery was obtained with all media (95 to 100%) except EE broth (74%). The incidence of competitive flora was significantly higher on selenite + brilliant green sulfa than on tetrathionate + bismuth sulfite; transfer volumes (10 and 1.0 ml) and preenrichment media did not contribute significantly to the presence of non-salmonellae on plating media. Characteristics of preenrichment media were found to be less critical than preenrichment incubation time for effective recovery of Salmonella in foods and feed ingredients. The use of 1.0- rather than 10-ml preenrichment transfer volume is indicated because it proved to be completely reliable under our experimental conditions and reduced the cost of analyses.

Surfactants for the Effective Recovery of Salmonella in Fatty Foods

1982 ◽  
Vol 45 (3) ◽  
pp. 249-252 ◽  
Author(s):  
J.-Y. D'AOUST ◽  
C. MAISHMENT ◽  
P. STOTLAND ◽  
A. BOVILLE
Keyword(s):  
Salmonella Enteritidis ◽  
Brilliant Green ◽  
False Negative ◽  
Tween 80 ◽  
Food Samples ◽  
Nutrient Broth ◽  
Tween 20 ◽  
Negative Results ◽  
False Negative Results ◽  
Tween 60

Inhibitory concentrations of 8 surfactants were determined for Salmonella typhimurium and Salmonella enteritidis. Pure culture work resulted in the exclusion of Tween 20, Teepol 610 and Brij 35 and retention of Tergitol-7 (T-7), Tween 80 (TW 80), Triton X-100 (TX), Myrj 52S (M), and Arlacel 80 + Tween 60 (AT) for a study on the quantitative recovery of Salmonella in 45 naturally contaminated fatty foods. Replicate food samples (100 g) were preenriched overnight at 35 C in nutrient broth supplemented with 3%(w/v) surfactant except AT (10%). Serial dilutions of preenrichment cultures were selectively enriched overnight in tetrathionate brilliant green (43 C) and selenite cystine (35 C) broths and streaked on bismuth sulfite and brilliant green sulfa agar media. Recovery with all test surfactants was comparable to that obtained with nutrient broth controls; of 270 preenrichment cultures tested, only 7 false-negative results attributable to TX (3), AT (2), M (1), and nutrient broth control (1) were obtained. None of the surfactants consistently yielded greater populations of Salmonella for given foods or food categories; median counts for preenrichment cultures were 104–105 salmonellae/ml for low and high moisture foods and 106–107 salmonellae/ml for animal feeds. These results suggest that use of surfactants to facilitate detection of Salmonella in fatty foods is not warranted.

Efficacy of an International Method for Detection of Salmonella in Chocolate and Cocoa Products

1984 ◽  
Vol 47 (2) ◽  
pp. 111-113 ◽  
Author(s):  
J.-Y. D'AOUST ◽  
A. SEWELL
Keyword(s):  
Brilliant Green ◽  
False Negative ◽  
Positive Sample ◽  
Negative Results ◽  
False Negative Results ◽  
Toxic Agents ◽  
Cocoa Products ◽  
Agar Media ◽  
Limited Sensitivity

The methods of the International Office of Cocoa and Chocolate and International Sugar Confectionery Manufacturers' Association (IOCC/ISCMA), and of the Health Protection Branch (HPB) were compared for their ability to detect Salmonella in chocolate and cocoa products. Of 152 samples tested, 13 contaminated samples were identified, 10 by the HPB and 8 by the IOCC/ISCMA method. Prolonged (48 h) incubation of enrichment media produced two false-negative results each with the Muller-Kauffman tetrathionate and the selenite cystine broths, exerted no effect on tetrathionate brilliant green, and identified one additional positive sample with the selenite brilliant green broth. More samples were found positive on bismuth sulfite than on brilliant green and brilliant green sulfa agar media. The present study underlines the limited sensitivity of both standard methods and questions the determinant role of casein in the neutralization of toxic agents in cocoa products.

Be aware of Shiga-toxin 2f-producing Escherichia coli: case report and false-negative results with certain rapid molecular panels

2020 ◽  
Vol 98 (4) ◽  
pp. 115177
Author(s):  
Aurélie Cointe ◽  
André Birgy ◽  
Alice Pascault ◽  
Ferielle Louillet ◽  
Alice Dufougeray ◽  
...  
Keyword(s):  
Escherichia Coli ◽  
Case Report ◽  
Shiga Toxin ◽  
False Negative ◽  
Negative Results ◽  
False Negative Results

Utilization of Fluorogenic Assay for Rapid Detection of Escherichia coli in Acidic Fruit Juice

2002 ◽  
Vol 65 (12) ◽  
pp. 1943-1948 ◽  
Author(s):  
STEVEN PAO ◽  
CRAIG L. DAVIS ◽  
LORETTA M. FRIEDRICH ◽  
MICKEY E. PARISH
Keyword(s):  
Escherichia Coli ◽  
Fruit Juice ◽  
Uv Light ◽  
False Negative ◽  
Enzyme Reaction ◽  
Inhibitory Effect ◽  
Sample Sizes ◽  
Citrus Juice ◽  
Negative Results ◽  
False Negative Results

This study was undertaken to investigate interference by acids commonly found in fruit juice in Escherichia coli assays involving the use of 4-methylumbelliferyl-β-d-glucuronide (MUG) as a fluorogenic substrate for enzyme reaction. Fluorescence intensity was negatively correlated (P < 0.001) with the volume of fresh citrus juice tested by the lauryl tryptose broth (LST)-MUG assay, and the permissible sample sizes were limited to 0.3 and 0.5 ml for fresh citrus juices with pHs of 3.3 and 3.9, respectively. In addition, false-negative results were visually observed under UV light when the E*Colite assay was used to test large volumes (5 to 10 ml per test) of fresh citrus juice or when the test broth used for the LST-MUG assay was supplemented with citric, malic, or tartaric acid at 2 to 4 g/liter. These results suggest that the size and pH of acidic samples should be controlled in MUG-based fluorogenic assays. The inhibitory effect on fluorescence was due to high acidity, which reduces fluorescence from 4-methylumbelliferone. Buffering improved the assays. When sodium bicarbonate was incorporated in the enrichment broth at 10 g/liter, the permissible sample sizes for fresh grapefruit juice (pH 3.1) increased from 0.3 to 1 ml for the LST-MUG (with 9.9 ml of broth) assay and from 3 to 10 ml for the E*Colite (with 99 ml of broth) assay.

Spatial Distribution of Salmonella, Escherichia coli O157:H7, and Other Bacterial Populations in Commercial and Laboratory-Scale Sprouting Mung Bean Beds

2005 ◽  
Vol 68 (12) ◽  
pp. 2510-2518 ◽  
Author(s):  
R. HORA ◽  
M. KUMAR ◽  
L. GARCIA ◽  
B. SCHUMACHER ◽  
J. ODUMERU ◽  
...  
Keyword(s):  
Escherichia Coli ◽  
Irrigation Water ◽  
Water Samples ◽  
Mung Bean ◽  
False Negative ◽  
Bacterial Populations ◽  
Negative Results ◽  
False Negative Results ◽  
Thermotolerant Coliforms ◽  
Microbiological Status

The reliability of testing spent irrigation water to assess the microbiological status of sprouting mung bean beds has been investigated. In commercial trials, the distribution of opportunistic contaminants within 32 bean sprout beds (25 kg of mung beans per bin) was assessed 48 h after germination. The prevalence of generic Escherichia coli, thermotolerant coliforms, and Aeromonas in sprouts (n = 288) was 5, 11, and 39%, respectively, and 57, 70, and 79% in the corresponding spent irrigation water samples (n = 96). Contamination was heterogeneously distributed within the seedbed. In laboratory trials, beans inoculated with a five-strain cocktail of either Salmonella or E. coli O157:H7 (103 to 104 CFU/g) were introduced (1 g/500 g of noninoculated seeds) at defined locations (top, middle, or base), and the beans were then sprouted for 48 h. When seeds inoculated with pathogens were introduced at the base or top of the seedbed, the pathogens were typically restricted to these sites and resulted in 44% of the spent irrigation water samples returning false-negative results. Introducing inoculated beans into the middle or at the presoak stage enhanced the distribution of both pathogens within the subsequent sprout bed and resulted in comparable levels recovered in spent irrigation water. The study demonstrated that even though screening a single sample of spent irrigation water is more reliable than testing sprouts directly, it does not provide an accurate assessment of the microbiological status of sprouting mung bean beds. Such limitations may be addressed by ensuring that bean batches are mixed prior to use and by taking spent irrigation water samples from multiple sites at the latter stages of the sprouting process.

Update on Preenrichment and Selective Enrichment Conditions for Detection of Salmonella in Foods

1981 ◽  
Vol 44 (5) ◽  
pp. 369-374 ◽  
Author(s):  
JEAN-YVES D'AOUST
Keyword(s):  
Nutritional Value ◽  
Brilliant Green ◽  
False Negative ◽  
Sterility Testing ◽  
Selective Enrichment ◽  
Cultural Methods ◽  
Negative Results ◽  
Limited Success ◽  
False Negative Results ◽  
Transfer Volumes

The search for short and sensitive cultural methods for detection of Salmonella in foods has met with limited success. Short (3–8 h) incubation of non-selective enrichment media do not provide conditions for effective resuscitation of stressed or injured salmonellae and result in unacceptably high numbers of false-negative results. Isolation of Salmonella is not dependent on the nutritional value of preenrichment media; simple media such as lactose and nutrient broths are equally reliable as highly nutritive sterility testing media. The need for detergents in non-selective enrichment of fatty foods and use of preenrichment transfer volumes greater than 1 ml is not indicated. Although selective enrichment in tetrathionate brilliant green (TBG) broth at an elevated temperature (43 C) increases method sensitivity, use of Mueller-Kauffman TBG under similar analytical conditions may be inhibitory to Salmonella. Refrigeration of preenrichment and selective enrichment broth cultures has been used successfully to provide greater analytical flexibility by increasing the number of days on which analyses can be initiated without engendering weekend work.

scholarly journals Single tube confirmatory tests forEscherichia coli

1980 ◽  
Vol 85 (1) ◽  
pp. 51-57 ◽  
Author(s):  
Keyword(s):  
Escherichia Coli ◽  
False Positive ◽  
False Negative ◽  
Gas Production ◽  
Single Tube ◽  
E Coli ◽  
Peptone Water ◽  
Confirmatory Tests ◽  
Laboratory Trial ◽  
The Difference

SummaryIn a multi-laboratory trial, lauryl tryptose mannitol broth (LTMB) and minerals-modified glutamate medium with added tryptophan (MMGM + T) were compared as single tube tests for the confirmation ofEscherichia coliin water; the confirmed results were also compared with the production of gas from minerals-modified glutamate medium without added tryptophan (MMGM). LTMB and MMGM + T gave similar gas and indole results with about 90% of the water samples in most of the laboratories. When compared with the ‘correct’ results as judged by acid and gas production from lactose peptone water and indole from tryptone water, the difference in the rate of false positive reactions between LTMB and MMGM + T was insignificant; but LTMB gave a significantly lower rate of false negative reactions than MMGM + T. Gas production from MMGM without added tryptophan gave significantly higher rates of both false positive and false negative reactions. Lauryl sulphate is therefore a suitable inhibitory surfactant for use in single tubemedia for the confirmation ofE. coli, which can be recommended.

Evaluation of a rapid fluorogenic method for the detection ofEscherichia coliin dairy products

1991 ◽  
Vol 58 (4) ◽  
pp. 477-483 ◽  
Author(s):  
Hassan R. Sarhan ◽  
Leslie R. Williams ◽  
Howard A. Foster
Keyword(s):  
Escherichia Coli ◽  
Klebsiella Pneumoniae ◽  
Dairy Products ◽  
Membrane Filtration ◽  
False Negative ◽  
Raw Milk ◽  
False Positive Reaction ◽  
Negative Results ◽  
False Negative Results ◽  
Soft Cheese

SummaryA rapid fluorogenic medium was evaluated for the detection ofEscherichia coliin dairy products. The medium was capable of detectingEsch. coliafter 7·5 h incubation at 41·5 °C. Samples of pasteurized milk (136), raw milk (63), soft cheese (60) and pasteurized cream (39) were examined with media based on 4-methylumbelliferyl-β-D-glucuronide (MUG-7) and Violet red bile agar and there were no significant differences between the numbers ofEsch. colidetected on the two media. MUG-7 medium had a specificity of 98·6% and the small number of organisms giving a false positive reaction were identified asKlebsiella pneumoniae. The incidence of false negative results was ∼2%. MUG-7 medium was suitable for pour plate, spread plate and membrane filtration methods. Possible applications of the method are discussed.

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