Advanced sample preparation for the molecular quantification of Staphylococcus aureus in artificially and naturally contaminated milk

Sample Preparation for qPCR Detection of Listeria from Food

Quantitative PCR, if performed properly, is a highly sensitive and robust tool. Nevertheless, its application to the particular case of pathogen detection from foodstuffs necessitates special requirements for reliable results. Firstly, a robust analytical chain, involving sample preparation and DNA isolation with purification, is necessary to ensure optimal performance. Secondly, for reliable quantification of Listeria monocytogenes from food, reproducible controls for all steps of the analytical chain are needed, which can give quantitative information about the performance of each individual step of the detection chain. Ideally, each individual sample should include a so-called internal sample process control (ISPC) which passes through all steps of the analytical chain and is phenotypically similar to the target organism (in this case L. monocytogenes).This chapter describes the modular and rapid (3 h) sample preparation method "matrix lysis" for the quantification of L. monocytogenes from food and gives detailed information regarding the application of an ISPC based on the example of the L. monocytogenes Δ-prfA/+IAC strain.

Staphylococcus aureusreservoirs during traditional Austrian raw milk cheese production

Sampling approaches following the dairy chain, including microbiological hygiene status of critical processing steps and physicochemical parameters, contribute to our understanding of howStaphylococcus aureuscontamination risks can be minimised. Such a sampling approach was adopted in this study, together with rapid culture-independent quantification ofStaph. aureusto supplement standard microbiological methods. A regional cheese production chain, involving 18 farms, was sampled on two separate occasions. Overall, 51·4% of bulk milk samples were found to beStaph. aureuspositive, most of them (34·3%) at the limit of culture-based detection.Staph. aureuspositive samples >100 cfu/ml were recorded in 17·1% of bulk milk samples collected mainly during the sampling in November. A higher number ofStaph. aureuspositive bulk milk samples (94·3%) were detected after applying the culture-independent approach. A concentration effect ofStaph. aureuswas observed during curd processing.Staph. aureuswere not consistently detectable with cultural methods during the late ripening phase, but >100Staph. aureuscell equivalents (CE)/ml or g were quantifiable by the culture-independent approach until the end of ripening. Enterotoxin gene PCR and pulsed-field gel electrophoresis (PFGE) typing provided evidence that livestock adapted strains ofStaph. aureusmostly dominate the post processing level and substantiates the belief that animal hygiene plays a pivotal role in minimising the risk ofStaph. aureusassociated contamination in cheese making. Therefore, the actual data strongly support the need for additional sampling activities and recording of physicochemical parameters during semi-hard cheese-making and cheese ripening, to estimate the risk ofStaph. aureuscontamination before consumption.

A novel flotation technique for the separation of nonadherent micro-organisms from a substrate

An understanding of adherence ability is crucial in many areas, for example, in research on biofilms, evaluation of probiotics or in biotechnology. In all these analyses, the reproducible washing is very important in the prevention of false results. During washing, the force, direction of the flow, position of the pipette tip, number of washing cycles, type of washing solution and the way of removing the washing solution can be sources of inappropriate stress to attached cells. To overcome these problems, we here propose the use of high mass density solutions as flotation agents. As the density of bacteria is lower than that of the flotation solutions, nonattached or weakly attached bacteria are moved to the surface due to hydrostatic force. Caesium chloride, ammonium nitrate and sodium diatrizoate solutions, which are commonly used as FAs, were compared with a standard method of rinsing. Several concentrations of agents were used to investigate the optimal concentration and influence of hydrostatic pressure on adhered micro-organisms. We show that flotation is a rapid method for distinguishing between adhered and weakly attached or loosed cells with reproducible results. Due to its range of possible mass density concentration, the best FA was shown to be caesium chloride.

SIGNIFICANCE AND IMPACT OF THE STUDY

This is the first study that suggests using flotation agents to separate planktonic from adhered bacteria. When a high-density solution is used, buoyancy of bacteria ensures their segregation in the solution. Flotation agents could be used instead of washing procedure, which is inaccurate and hardly reproducible. High-density flotation agents could be used for more precise evaluation of bacterial adherence in many assays, such as research of biofilms or evaluation of probiotics.

Rapid detection, characterization, and enumeration of foodborne pathogens

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.