Detection of microbial contaminants

The rapid and effective detection of microbial contaminants is key to the quality control of products in various industries such as pharmacology, cosmetology, or food-related industries. This allows for rapid release of stocks, guarantees a safe shipment of products, and the possibility to recall contaminated batches before their effective delivery to customers. Modern detection techniques for microbial contaminants usually target ubiquitous biomolecules found in all microorganisms.

Today, there are several alternative methods to reveal microbial contaminations. However, they have certain limitations :

• PCR-based identifications are detrimental for cells, generating false positives and/or false negatives. It delivers a molecular and non-phenotypical analysis, difficult to adapt to internal processes. In addition, it requires significant preparatory work (lysis, extraction).
• MALDI-TOF is a technique carried out on fresh bacterial cultures that may take a long time to prepare, with a delicate preparation step and complex protocols. It requires the destruction of the analysed cells. Identification is impossible beyond the species.
• Flow cytometry is a relevant application for industrial purposes because it allows for detection of organisms in real time and in a single live cell (analysis of up to 50,000 cells per second by flow cytometry). This technique makes it possible to pass through a filter of large volumes to concentrate the microorganisms (scanning cytometry). It also allows for detection of all cultivable and non-cultivable microorganisms.
• The use of conventional fluorogenic probes (CFDA and derivatives) in cytometry is compromised by significant noise problems: the released fluorophore is water soluble and diffuses out of the cells harbouring the target activity. The risk of a false positive is high, and the experiment calls for a complex protocol to quench the contaminating fluorescence.

In view of the severe limitations described above, the development of alternative tools holds great promise for applications where the detection of microorganisms is paramount: in the food industry, in cosmetology, and in pharmacology.