Health

The bacterium Listeria Analysis monocytogenes can be detected in humans.

The bacterium Listeria monocytogenes can be detected in humans.

Listeria bacteria are Gram-positive, facultatively anaerobic rods that do not produce spores and are present in nature. The six species and four subspecies of the genus include L. monocytogenes, L. innocua, L. welshimeri, L. Seeliger, L. ivanovii, and L. grey. Despite the fact that four species have been related to human illness, L.monocytogenes is by far the most common, accounting for the vast majority of human infections. Although the species has at least 13 different serotypes, all of which can cause Listeria Analysis, serotype 4b is the most common in humans.

  1. monocytogenes can cause serious infections that can be fatal. Pregnant women, newborn babies, the elderly, and those with impaired immune systems are most vulnerable. The infective dose for sensitive individuals is unknown, but in some situations, it could be quite low (less than 100 CFU/g). The incubation time is usually 30 days, although it can vary from 1 to 90 days. Initial flu-like symptoms are frequently followed by vomiting and diarrhoea, with potentially fatal meningitis and septicaemia developing in a few cases. Infection in pregnant women can cause miscarriage, and epidemics can have fatality rates of 30% or more.

Although pregnant women can transmit the infection to their foetuses, it is now thought that the infection is carried mostly through food and that human-to-human transmission is infrequent. Following a peak in the late 1980s, listeriosis prevalence in North America and Europe declined as the food industry introduced control measures. In recent years, the United States has reported roughly 1,600 cases of listeriosis per year, with approximately 260 deaths (Source: CDC). Around 1,470 cases were documented in Europe in 2011, however, the number of cases has started to climb again, especially among the elderly, for unexplained reasons. Foodborne outbreaks are still a serious problem, especially in North America. A statewide outbreak linked to cantaloupes in the United States, for example, resulted in at least 147 cases of illness and may have contributed to up to 33 deaths in 2011. (Source: CDC).

How can I check for Listeria Analysis in foods?

Listeria spp. and Listeria monocytogenes can be discovered in a variety of foods, however, the bulk of samples come from processed cold items such as dairy, Salmonella analysis cooked meats, and smoked fish. Environmental samples include swabs taken from food preparation surfaces and cold, damp places like drains and chillers.

Food and environmental samples should be analysed as soon as a feasible following collection. Alternatively, samples should be stored at 4 degrees Celsius if this is not possible. Despite the fact that the cells can survive in frozen foods, samples should be maintained frozen until testing.

Composite samples from individual food lots can be formed by mixing samples in enrichment broth media. 25g food samples are commonly cultivated in detection testing, and duplicate samples should be preserved for enumeration if a detection test produces a positive result.

What are the Traditional Listeria Detection Methods?

There are now ISO standard approaches for detecting and counting L. monocytogenes in food and animal feed. For L.monocytogenes, ISO 112901:1996 is a detection method, while ISO 112902:1998 is an enumeration method. Both techniques were revised in 2004 to account for new media. Other organizations, including the USFDA Bacteriological Analysis Manual, have produced similar Standard Techniques (BAMs).

The first step in traditional detection protocols for food and environmental samples is a pre-enrichment culture in a liquid media such as Buffered Listeria Enrichment Broth (BLEB) or HalfFraser broth, cultured at 30°C for 24 hours.  To limit the growth of competing microorganisms, selective agents may be present in the pre-enrichment media, although at lower concentrations than in selective enrichments.  Subculture the pre-enrichment culture into selective enrichment media, such as Fraser broth or Oxoid Novel Enrichment (ONE) Listeria broth and incubate for an additional 24 hours at 3537 degrees Celsius. 

Inoculate one or more selective agar plates with the selective enrichment culture and incubate at 37°C for 24 to 48 hours. The new ISO technique specifies the chromogenic medium Agar Listeria according to Ottaviani and Agosti (ALOA) and one other selective agar. Modified Oxford agar, Palcam agar, and LPM agar are just a few of the alternatives available, and they all rely on Listeria spp. to hydrolyze aesculin to form unique colonies.Another chromogenic agar medium specially created for the differentiation of L. monocytogenes is also available. Examples include ALOA® One Day Agar, Oxoid Chromogenic Listeria (OCLA) Agar and CHROMagarTM Listeria.

When detection methods for Listeria spp. or L. monocytogenes give a positive result for Listeria spp. or L. monocytogenes in food and environmental samples, it may be necessary to quantify the positive result. A popular procedure is to dilute the materials without addition in buffered peptone water or enrichment broth, smear each dilution onto ALOA or another selective agar medium, and incubate for 24-48 hours at 37oC. As a result, the number of typical colonies can be counted and checked.

What is the quickest way to get Listeria Analysis results?

Below is a list of kits that can test for Listeria in food and environmental samples fast. The results of traditional Listeria spp. detection tests can take up to five days. As a result, a range of alternative rapid screening procedures for food and environmental samples have been developed in order to provide faster results. Many of them are commercially accessible and have received AOAC and/or AFNOR certification. The AOAC library of performance-tested methods contains over 50 products for the fast detection of Listeria spp. and methicillin-resistant enterococci (MRSA). This is more than any other foodborne pathogen.

Listeria spp. and Listeria monocytogenes rapid test and screening kits use a variety of technologies, including immunomagnetic separation, EIA- and ELISA-based assays with fluorescent or colourimetric detection, simple lateral flow assays with immunochromatographic technology, and molecular techniques such as DNA hybridization and PCR-based essays, many of which now include real-time detection. Some procedures can be automated to filter a large number of samples. Almost all rapid test protocols include a selective enrichment culture that can be completed in as little as 24 hours, followed by rapid detection techniques to replace culture on selective agars and further confirmatory tests. Most claim to get results in half the time of traditional methods, while some PCR-based tests claim to be able to detect Listeria in as little as 30 hours.

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