OREANDA-NEWS. August 12, 2016. A BNVL food safety scientist interpreting mass spectrometry data of a meat sample: no food contaminants found (Photo: M. Gaspar/IAEA)

The staff members of the Botswana National Veterinary Laboratory use various nuclear, molecular, serological and isotopic techniques for the early and rapid diagnosis of various animal diseases and for testing meat samples for food contaminants. Here is how these techniques work: 

Contaminant testing

Radio receptor assay: These are easy-to-perform and accurate tests that analyse up to seven groups of veterinary antibiotics, mycotoxins and pesticides. In this test, binding agents, such as bacteria that selectively bind to the contaminants, are added to the sample, along with a version of the contaminant marked with a radioactive tracer. These include a radioactive isotope, typically tritium (3H) or carbon-14 (14C). If the sample is contaminated, the contaminant in the food sample is competing with the marked contaminant, so less of the latter is bound. If the sample contains no drug residues or other contaminants, the agent binds exclusively with the tracer-marked additive. This difference can be measured and the amount of contaminant, if any, identified.

Liquid chromatography with mass spectrometry: This analytical “finger printing” technique is used to detect and identify very low concentration levels of chemicals, in this case food contaminants, and distinguish them from other material. High performance liquid chromatography (HPLC) is used to separate, identify and quantify each component in a mixture. The different components of the mixture react differently with the material in the chromatography tool, which provides the basis for the distinction. The mass spectrometer, at the same time, identifies chemicals based on their molecular masses. While the two tools combined provide a more precise measurement than each one would do individually, the addition of stable isotopes as reference material improves the reliability of the technique.

Detecting animal pathogens though molecular techniques

Polymerase chain reaction (PCR): This technique is used to replicate, or amplify, a specific region of DNA billion-fold in just a few hours. The detection of the amplification of the target DNA is then monitored by either radio-isotopes or by fluorescent molecules. PCR is the most sensitive method to detect microbial pathogens in clinical specimens. It is also very specific, as it usually targets a specific marker on a given pathogen.

PCR consists of repeated heating and cooling, causing separation of the two DNA-strands and then replication of the original DNA.  This procedure gets repeated until enough copies of the targeted molecule are available. Scientists can then identify the presence of the pathogen’s genome.

Real time PCR (qPCR): This is technique is a variant of PCR, where the PCR reaction can be analysed as the amplification takes place. The advantage over standard PCR is that real time PCR is ‘live’ and less prone to handling contamination and is therefore the preferred approach.