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For the listeria experiment, what is the theoretical limit of detection for the enrichment procedure and what are the advantages of using two selective enrichment procedure than just one?

For this question, the solution depends on which type of enrichment methods used to detect the Listeria monocytogenes found in foods. Listeria monocytogenes is a foodborne pathogen commonly present in foods, such as dairy products, meats, vegetables, and seafood. (1 ) Listeria monocytogenes can cause listeriosis, and the most common symptoms are meningitis, encephalitis, septicaemia, and flu-like symptoms. (1) Pregnant women that are infected with Listeria monocytogenes can result in premature birth. (1) In the US, the tolerance level for the presence of L. monocytogenes allow in food is zero. (1) This means that the detection level for listeria should be very low. (1)
The are several methods for the detection of listeria and each of these culture-based methods have a different theoretical limit of detections.

In the method developed by the FDA for the detection of L. monocytogenes in dairy, fruit, vegetable, and seafood; the theoretical limit of detection is < 0.7 cfu/ml. (1) The theoretical limit of detection is the lowest concentration of Listeria cells that can be detected by the procedure. In this case, it is less than 0.7 colony forming units/ ml.

The steps in the enrichment for this method required the growth in FDA enrichment broth (FDA-EB) containing naladixic acid, acriflavine, cycloheximide for 24 hour at 30 degree Celsius. (1) Then, the culture is further subcultured and enriched by selectively using FDA-EB media and incubate for 48 hour at 30 degree Celsius. (1) After this, the subculture is plated onto Oxford and LPM agars for the further isolation of Listeria colonies. (1) To further validate the Listeria colonies, biochemical and metabolic assays must be performed in order to confirm their identification. (1) After the enrichment steps, additional tests must be performed to confirm the identity of the Listeria species. (1) The physiology of the Listeria should be determined using gram-staining and catalase activity testing. (1) If the culture is positive for Listeria, the cells should be gram positive and positive for catalase activity. (1) The culture should also be tested for the ability to induce haemolysis on blood agar, and for mannitol degradation. (1)

In contrast, another method approved by the International Organization for Standardization (ISO) required that the theoretical limit of detection for the enrichment of Listeria to be between 5-100 cfu/25g from all foods. (1) This means that the lowest level of Listeria cells that can be detected by this method is between 5-100 colony forming units/ 25 g of food.

This method utilized a different media for the enrichment of the Listeria. The Listeria is cultured in Fraser broth for 24 h at 30 degree Celsius, and then subcultured in Fraser broth containing ammmonium iron (III) citrate, acriflavine, and nalidixic acid for 48 hour at 37 Celsius. (1) In addition, the culture is further enriched with PALCAM or Agar Listeria Ottavani and Agosti (ALOA) plates. (1) The purpose of the ALOA plates is to distinguish one Listeria species from another. In this case, ALOA plate is selective for L. monocytogenes. (1)

Another method of enrichment developed by the Netherlands Government Food Inspection Service (NGFIS) has a theoretical limit of detection for the enrichment procedure to be about < 10 cfu/g in all foods, especially meat, fermented sausage, mushroom, and cheese. (1) This means that the lowest level of Listeria cells that can be detected in food is < 10 colony forming units/ gram of food.

In this method, the Listeria is grown in Listeria enrichment broth (LEB) at 30 Celsius for 48 hours, and subcultured onto PALCAM agar. (1) PALCAM agar is used to distingush between L. monocytogenes and other species in the culture. (1)

The advantages in using two or more selective enrichment methods rather than just one is that the success of the culturing of Listeria depends on how selective the media tend to become. One media may be more selective than another. So using additional selective media to subculture the Listeria can be very beneficial in the purification of the Listeria, and help in the identification of the optimum detection limit. (1) The requirement for more than one enrichment methods can selectively distinguished between target organisms and others non-target competitors in the same culture. (1) Ideally, the enrichment and detection method should be sensitive enough to detect organisms as low as 1 cell/g of food material, and be specific only to the target pathogen within the genus. (1) Using more than one methods can accurately detect the Listeria, and prevent false positives.

The theoretical limit of detection is the lowest level of concentration that can be detected by the listeria experiment. For example, if the lowest detection concentration of Listeria cells in the culture is 5 cfu/ml. That means that it only takes 5 colony forming units per 1ml of culture for the culture to be positive for Listeria.

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For the listeria experiment, what is the theoretical limit of detection for the enrichment procedure and what are the advantages of using two selective enrichment procedure than just one?

For this question, the solution depends on which type of enrichment methods used to detect the Listeria monocytogenes found in foods. Listeria monocytogenes is a foodborne pathogen commonly present in foods, such as dairy products, meats, vegetables, and seafood. (1 ) Listeria monocytogenes can cause listeriosis, and the most common symptoms are meningitis, encephalitis, septicaemia, and flu-like symptoms. (1) Pregnant women that are infected with Listeria monocytogenes can result in premature birth. (1) In the US, the tolerance level for the presence of L. monocytogenes allow in food is zero. (1) This means that the detection level for listeria should be very low. (1)
The are several methods for the detection of listeria and each of these culture-based methods have a different theoretical limit of detections.

In the method developed by the FDA for the detection of L. monocytogenes in dairy, fruit, vegetable, and seafood; the theoretical limit of detection is < 0.7 cfu/ml. (1) The theoretical limit of detection is the lowest concentration of Listeria cells that can be detected by the procedure. In this case, it is less than 0.7 colony ...

Solution Summary

Listeria monocytogenes is a foodborne pathogen commonly present in foods, such as dairy products, meats, vegetables, and seafood. (1 ) Listeria monocytogenes can cause listeriosis, and the most common symptoms are meningitis, encephalitis, septicaemia, and flu-like symptoms. (1) Pregnant women that are infected with Listeria monocytogenes can result in premature birth. (1) In the US, the tolerance level for the presence of L. monocytogenes allow in food is zero. (1) This means that the detection level for listeria should be very low. (1)
The are several methods for the detection of listeria and each of these culture-based methods have a different theoretical limit of detections. In the method developed by the FDA for the detection of L. monocytogenes in dairy, fruit, vegetable, and seafood; the theoretical limit of detection is < 0.7 cfu/ml. (1) The theoretical limit of detection is the lowest concentration of Listeria cells that can be detected by the procedure. In this case, it is less than 0.7 colony forming units/ ml.

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Edit of a Contractor Letter

Can you please correct sentences. Please re - write the sentences and please re - write the whole sentences.. Please use high vocabulary words. Please add few more line sentences... Here is the information....

Dear Contractor,

For the above referenced project. These revisions and / or clarifications shall supercede and take precedence over previously issued Technical information specifications. We encourage proponent to review the below information prior to submitting a proposal. Each proponent must acknowledge upon receipt of this addendum.

A. REVISION OF RFP

1.1 WORK INCLUDES, BUT IS NOT LIMITED TO THE FOLLOWING TASKS:

The engineering services includes designing and implementing a proximity detection system, but is not limited to the following tasks. Please note, during the submission of the proposal, proponent can provide recommendations, suggestions and opportunities for improvement that will enhance the project.

Below information and following specifications are just scenarios it just for reference only.

Signal:

The pedestrian proximity device should be able to send a signal to the haul trucks at a distance of at least 5 m (16 feet) to ensure that the truck operator is aware of any personnel in the vicinity. The system should also indicate a warning in the form of a buzzer, beacon, or LED to alert the truck driver, and pedestrian that they are close to each other. This device should automatically activate the warning signal. When reversing a large truck, the proximity device should send a warning signal to pedestrian within approximately 3 m (10 feet), and side detection of haul trucks up to approximately 2 m (7 feet).

For Continuous mining machine the proximity device should send a signal to pedestrian within approximately 2 m (7 feet) to prevent any accident from occurring.

Speed Warning:

The proximity device should provide a warning system to limit the travel speed of the haul trucks. If a truck operator reaches the set speed limit then a warning in the form of a beacon, buzzer, or LED will be activated. As the Expo underground mine site has set speed limit of 50 KM / H.

Working Condition:

This proximity detection system should operate in extreme conditions where electrical noise gas, dust, temperature (0 C - 30 C) or Humidity fluctuations are present. It must not cause electrical interference to the existing phone, PLC and radio communications networks. Interference received must be accepted, including interference that may cause undesired operation.

Modification:

The system should allow authorized personnel to specify the set point values for the warning.

Safety:

Ability to circumvent the proximity detection system in the event of an emergency where operator intervention is immediately required. The system should distinguish conditions that occur due to nuisance, and act accordingly. The company safety standards have to be met by the system.

Shut Down: - Eliminated for Scope of Work

Shut down of the large haul truck or Continuous miner has been eliminated from scope of work. Reason for elimination it would breach of the manufacturer's warranty of the large haul truck or continuous miner.

No Stop:

As per Addendum Notification # 3 decided not to stop the large haul trucks (or) Continuous miner machine, as it was already been decided that this is potentially dangerous. As long as the proximity detection system can send signal to pedestrian to prevent any accident from occurring at set point values for the warning. Reason for elimination of stopping the large haul trucks or Continuous Miner Machine as it would be a breach of the manufacturer's warranty.

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