Evaluation of the use of conductimetry for the rapid and precise measurement of Salmonella spp. growth rates

The growth rates of 14 Salmonella serovars in tryptone soy broth plus yeast extract (TSBYE) were estimated using conventional plating techniques and indirect conductimetry using a Don Whitley RABIT system. Both methods gave identical results for the maximum specific growth rate (μmax) P > 0.05. However, using the conductimetric method, μmax for a single serovar was determined in less than 7 h, whereas the conventional method required an additional 24 h. In addition, the conductimetric method was considerably more precise, much less labour-intensive and required the use of considerably less consumables. Using conductimetry, a trained operator could accurately determine μmax for 24 serovars in 3 working days, but only one serovar using the conventional plate counting technique. Hence, the use of conductimetry can markedly increase the precision and accuracy of μmax determinations by allowing a very significant increase in the number of results obtained and in their precision. The data generated will allow the development of better mathematical growth models. The method can also be used to compare growth media and conditions and hence rapidly optimise detection protocols for this pathogen.