Abstract
This article describes a method for high-throughput competition assays using a bioluminescent strain of L. monocytogenes. This method is based on the use of the luminescent indicator strain L. monocytogenes EGDelux. The luminescence of this strain is correlated to growth, which make it suitable to monitor the growth of L. monocytogenes in mixed cultures. To this aim, luminescence kinetics were converted into a single numerical value, called the Luminescence Disturbance Indicator (LDI), which takes into account growth inhibition phenomena resulting in latency increase, decrease in the luminescence rate, or reduction of the maximum luminescence. The LDI allows to automatically and simultaneously handle multiple competition assays which are required for high-throughput screening (HTS) approaches. The method was applied to screen a collection of 1810 strains isolated from raw cow’s milk in order to identify non-acidifying strains with anti-L. monocytogenes bioprotection properties. This method was also successfully used to identify anti-L. monocytogenes candidates within a collection of Lactococcus piscium, a species where antagonism was previously described as non-diffusible and requiring cell-to-cell contact. In conclusion, bioluminescent L. monocytogenes can be used in HTS to identify strains with anti-L. monocytogenes bioprotection properties, irrespectively of the inhibition mechanism.
Highlights
Constant efforts are being made to ensure food safety, foodborne illnesses remain a major concern in developing and developed countries (Wang et al, 2016)
Cultivation of the strain L. monocytogenes EGDelux in TSBYE broth revealed that the major production of luminescence occurred during the exponential growth phase (Figure 1A)
The results show that kinetics of luminescence reflects the growth behavior; and that luminescence reduction can be used as an indicator of L. monocytogenes growth inhibition
Summary
Constant efforts are being made to ensure food safety, foodborne illnesses remain a major concern in developing and developed countries (Wang et al, 2016). In France, from 2008 to 2013, it is estimated that fifteen foodborne pathogens led to 1.28–2.23 millions ill patients and 250 deaths (Van Cauteren et al, 2017). Food safety is an important economic issue: in the United States, the annual economic impact of health loss is estimated as more than 77 billions dollars (Scharff, 2012). Microorganisms can induce food spoilage leading to food waste (Barth et al, 2009; Remenant et al, 2015; Leyva Salas et al, 2017). Reducing food waste is a major challenge since each year 1.3 billions tons of food are lost or wasted (Gustavsson et al, 2011)
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