A novel approach using growth curve analysis to distinguish between antimicrobial and anti-biofilm activities against Salmonella

Salmonella spp. are a commonly identified cause of outbreaks of food-borne diseases. Despite much research, there remains the need to find new antimicrobial and anti-biofilm agents against Salmonella. For this, it is necessary to distinguish between these two aspects. Agents that influence biofilm formation should not affect bacterial growth, to thus avoid further promotion of the development of resistance. In this study, we present the use of growth curves of Salmonella Infantis to simultaneously determine antimicrobial and anti-biofilm activities, for the screening for anti-Salmonella activities of 42 aqueous fungal extracts. The extract from Pseudohydnum gelatinosum showed good antimicrobial activity, and that from Pleurotus ostreatus showed good anti-biofilm activity. In extracts from Infundibulicybe geotropa and Infundibulicybe gibba, both activities were determined after fractionation. The antimicrobial activity was associated with protein-rich fractions and mediated by L-amino acid oxidase activity. The fractionation did not allow determination of the anti-biofilm active fraction, so further studies are needed to define these compounds. Growth curve analysis of S. Infantis is shown here to provide a fast and simple approach to distinguish between antimicrobial and anti-biofilm activities in a high-throughput setting, such that it can be easily implemented in screening and further bioassay-based purification of novel alternatives to antibiotics