ASSESSING FUNGAL INTERACTION WITH THE FOODBORNE PATHOGEN LISTERIA MONOCYTOGENES

Abstract

Listeria monocytogenes is a Gram-positive bacilli-shaped species that is pathogenic to humans and animals. This bacterial species is a major concern for food safety as it is a major cause of food poisoning in the US and throughout the world. L. monocytogenes is also a deadly enteric pathogen that leads to intense illness and even death in livestock, which is a serious concern for the meat industry and veterinary medicine. A previous study found that some endophytic fungi may have an inhibitory effect on the growth of Listeria and thus may represent a possible source for the identification of new antibiotics against the pathogen. Here, I investigated and assessed the interactions of 36 additional fungal species with Listeria. Fungi were grown alone and in coculture with Listeria to assess whether fungi could overgrow the pathogen. Subsequently, fungi originating from either each co-culture or monoculture were placed on a lawn of Listeria (i.e., spot on the lawn assay) to assess whether fungi were cytotoxic or inhibitory to Listeria, which was measured via zone of bacterial inhibition. In addition, I tested the hypothesis that fungi grown in co-culture prior to the spot on the lawn assay would be better "primed" to respond to Listeria than fungi grown alone in monoculture. Overall, I found no fungi were cytotoxic or inhibitory to Listeria, yet I observed a significant increase in fungal growth on a lawn of Listeria when fungi were previously exposed to Listeria. These findings imply that fungi can sense thepresence of Listeria when grown together and alter their growth in response, even when bacterial cells and fungal hyphae do not make contact. Further research is needed to investigate how this process occurs and what metabolites are being secreted as a form of communication between the microorganisms.