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Fourier transform infrared (FTIR) spectroscopy is a technique which enables the mutual comparison and clustering of infrared spectra of various bacteria. The results can be used when formulating a specific farm approach for the detected strains of bacteria.

Typification of bacteria strains

Research has shown that FTIR spectra of various strains all belonging to the same species of bacteria often differ sufficiently to allow a distinction to be made between the strains. These differences, however minimum they may be, have proven to be extremely reproducible, as long as they are approached in a very standardised manner. Advanced correlation and cluster analysis techniques are applied to analyse the generated spectra.


Using FTIR spectroscopy, a possible relationship to other bacterium isolates can be determined relatively quickly and at a much lower cost than DNA sequential analysis.

The use of FTIR spectroscopy

Simply identifying the presence of a bacterium often will not suffice in determining the appropriate strategy to combat it. It is becoming increasingly necessary to determine specific characteristics of the pathogen in question in order to determine whether an epidemiological link exists, including further typification, virulence properties or resistance to certain therapeutics.

When problems recur at a farm, FTIR spectroscopy is a useful tool, for example when combating Streptococcus suis. An important question at that point is whether the issues are caused by related strains or by new strains in each case.

FTIR spectroscopy can also prove useful in detecting the source of an outbreak. In the event of a mastitis outbreak caused by Streptococcus uberis, isolates from milk, bedding and manure can be compared in order to gain insight into sources of contamination and transmission routes.

GD offers cluster analysis for the following bacteria strains

  • Erysipelothrix rhusiopathiae
  • Escherichia coli
  • Klebsiella pneumoniae
  • Listeria monocytogenes
  • Mannheimia haemolytica
  • Pasteurella multocida
  • Salmonella Typhimurium
  • Staphylococcus aureus
  • Streptococcus agalactiae
  • Streptococcus uberis
  • Streptococcus suis

Besides the availability of cluster analysis for these bacteria strains, we are also working at establishing and validating methods for cluster analysis of even more strains. In doing so we apply models, making use of artificial intelligence, with which isolates can be classified into serotypes based on the differences in infrared spectra, for example.

FTIR technique

Fourier transform infrared (FTIR) spectroscopy is a fast and relatively inexpensive technique for measuring intramolecular vibrations in chemical bonds. A chemical bond between two atoms is not rigid. The atoms are constantly moving relative to each other. Just as coloured substances absorb light, chemical bonds can absorb frequencies of infrared light through their vibrations. The amount of light absorbed at each frequency depends on the chemical nature of the bond. The infrared spectrum of a bacterium is therefore determined by the biochemical composition of the bacterial cell.

There is a lot involved in carrying out this technique. A pure culture is prepared under highly standardised conditions, with strict limits on incubation temperature and time. The preparation of a suspension of the colony material and its application to the target plate, which is then presented to the instrument, also requires a highly standardised procedure.

The process from preparing a colony suspension to generating a spectrum takes several hours, with around 20 isolates tested per run. The computer programme that analyses the spectra makes a statement about the relationship of the isolates within seconds, based on the IR spectra generated. FTIR spectroscopy can therefore be used to determine a possible relationship with other isolates of the same bacterial species relatively quickly and at a much lower cost than DNA sequence analysis.

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