Rapid detection, characterization, and enumeration of foodborne pathogens

Abstract

As food safety management further develops, microbiological testing will continue to play an important role in assessing whether Food Safety Objectives are achieved. However, traditional microbiological culture-based methods are limited, particularly in their ability to provide timely data. The present review discusses the reasons for the increasing interest in rapid methods, current developments in the field, the research needs, and the future trends. The advent of biotechnology has introduced new technologies that led to the emergence of rapid diagnostic methods and altered food testing practices. Rapid methods are comprised of many different detection technologies, including specialized enzyme substrates, antibodies and DNA, ranging from simple differential plating media to the use of sophisticated instruments. The use of non-invasive sampling techniques for live animals especially came into focus with the 1990s outbreak of bovine spongiform encephalopathy that was linked to the human outbreak of Creutzfeldt Jakob's Disease. Serology is still an important tool in preventing foodborne pathogens to enter the human food supply through meat and milk from animals. One of the primary uses of rapid methods is for fast screening of large number of samples, where most of them are expected to be test-negative, leading to faster product release for sale. This has been the main strength of rapid methods such as real-time Polymerase Chain Reaction (PCR). Enrichment PCR, where a primary culture broth is tested in PCR, is the most common approach in rapid testing. Recent reports show that it is possible both to enrich a sample and enumerate by pathogen-specific real-time PCR, if the enrichment time is short. This can be especially useful in situations where food producers ask for the level of pathogen in a contaminated product. Another key issue is automation, where the key drivers are miniaturization and multiple testing, which mean that not only one instrument is flexible enough to test for many pathogens but also many pathogens can be detected with one test. The review is mainly based on the author's scientific work that has contributed with the following new developments to this field: (i) serologic tests for large-scale screening, surveillance, or eradication programs, (ii) same-day detection of Salmonella that otherwise was considered as difficult to achieve, (iii) pathogen enumeration following a short log-phase enrichment, (iv) detection of foodborne pathogens in air samples, and finally (v) biotracing of pathogens based on mathematical modeling, even in the absence of isolate. Rapid methods are discussed in a broad global health perspective, international food supply, and for improvement of quantitative microbial risk assessments. The need for quantitative sample preparation techniques, culture-independent, metagenomic-based detection, online monitoring, a global validation infrastructure has been emphasized. The cost and ease of use of rapid assays remain challenging obstacles to surmount.

Implications of Electrical Impedance-Based Microbiological Technology in Pork Meat Processing Industry for the Rapid Detection and Quantification of Salmonella Spp.

“…Only differences between results given by plate and impediometry appear for high levels of bacteria since the slope of the regression line becomes higher than 1. This fact may indicate a higher sensitivity of impediometry (112% ± 2%) against standard count plate (100%) which is in agreement with Donaghy and Madden [18], Bolton and Gibson [13], Quinn et al [21], Wawerla et al [22], Hoorfar [8] and Russell [14]. Moreover, higher errors are attained by standard plate count (horizontal error bars) compared to those of impedance-based method (vertical error bars) which reduces the reproducibility of the quantification assay when using classic microbiology [14,28].…”

“…As a strategy, over the past decades, numerous rapid methods have been developed to shorten the assay time and increase its sensitivity [1,8]. Moreover, since pathogenic distribution is irregular in the final product and a high throughput screening is required for a large number of samples, there may be a tool for fast screening to identify positive samples, allowing the release of negative samples to the market.…”

“…Although they have notably reduced the assay time and improved the detection limit, they also show some shortcomings including long times of pre-or postenrichment [7,9]; cross or inhibited reactions by compounds or background flora from some food matrices; variation of antigens and DNA of the target pathogen [1,[7][8][9][10]. Moreover, ELISA shows low suitability in the binding between Salmonella and its antibodies, whereas PCR involves far away more costs, labour-intensive tasks [11] and cannot distinguish between death, supposedly non-pathogenic, and viable cells.…”

Development of Direct Real-Time PCR System Applicable to a Wide Range of Foods and Agricultural Products

“…The analytical targets of the tests are diverse and include food allergens 1) , foodborne pathogens 2) , genetically modified organisms (GMOs) . In many industrialized countries, the consumers of these products are paying greater attention to the quality and authenticity of food.…”

Use of Accuracy Profile Procedure to Validate a Real-Time PCR Method to Quantify Bacteria in Feces

“…everal methods have been developed to numerate bacteria in biological and environmental samples; those for foodborne pathogens have been reviewed by Hoorfar (1). Sophisticated methods of molecular analysis of feces are being used to identify species and enumerate bacteria (2,3).…”