Developed biofilm assay suggests Escherichia coli Nissle 1917 may mediate biofilm inhibition in Escherichia coli K-12 in liquid co-culture


Alex Fung, Anderson Li, Helen Lin, Vivian Li

Volume 24
Fall 2018 / Winter 2019

Escherichia coli K12 (K12) is a bacterial species known to form biofilm, which is a community of bacteria residing in a matrix of secreted polysaccharides and
proteins. This leads to reduced efficacy in conventional antibiotic regimens, and may cause chronic infections in patients. Escherichia coli Nissle 1917 (EcN), a probiotic strain, has been shown to decrease biofilm formation of co-cultured strains of Escherichia coli (E. coli); however, this mechanism is not well understood. We hypothesize that EcN mediated inhibition of biofilm formation of co-cultured E. coli strains involves the CpxA/CpxR twocomponent signaling system in the Cpx pathway which inhibits biofilm formation. Thus, we expect that when EcN is co-cultured with E. coli strain K12, biofilm formation will be reduced. CpxA indirectly deactivates the Cpx pathway, whereas CpxR activates the Cpx pathway. By using genetic knockouts of cpxR and cpxA, we expect to see that a ΔcpxR knockout will show increased biofilm formation, while a ΔcpxA knockout will show reduced biofilm formation. Here, we demonstrate that EcN may have inhibitory effects on
the development of K12 biofilm in liquid co-cultures. This was determined by quantifying and comparing crystal violet stains of biofilm formation at the air-liquid-solid interface in glass test tubes, which is shown here to enhance biofilm formation. Although the findings were not conclusive to address our original hypothesis, our results led to the development of a biofilm assay for direct detection and quantification of biofilm formation, laying the groundwork for future experiments.