Measuring Aggregation of DH5α Escherichia coli Cells in Mildly Acidic pH Conditions to Suppress the Expression of Fimbriae

Abstract

Autoaggregation is a process by which individual cells naturally clump together, due to interactions between self-recognizing surface structures. This process carries diverse implications, where autoaggregation can act as a defense mechanism for the microorganisms to form resilient communities and biofilms. Fimbriae are hair-like appendages on the surface of bacterial cells that can block the aggregation function of autotransporters like Antigen 43 in Escherichia coli cells. However, the function of fimbriae can be suppressed by environmental factors like pH, effectively reducing their ability to mediate cell-cell interactions. Adjusting such environmental conditions to suppress fimbriae expression allows for a better understanding of other autotransporters and factors regulating autoaggregation. The autoaggregation assay method is used to assess the ability of microorganisms to self-aggregate, and it involves measuring the rate of aggregation of cells in a liquid medium suspension over time. In this assay, microbial cells are cultured to a predetermined optical density, then gently mixed for homogeneity. Overtime, cells aggregate, forming visible clumps that settle at the bottom of the culture tube. The degree of autoaggregation is measured in a spectrophotometer by measuring optical density over time. This methods paper outlines the protocol that can be used for conducting an aggregation assay of DH5α Escherichia coli to explore the role of autotransporters such as Antigen 43 while suppressing fimbriae expression by changing the environmental pH of the growth medium.