Urinary tract infections (UTI) are one of the most common and costly infections worldwide, with the primary cause being uropathogenic Escherichia coli (UPEC). UPEC undergo a multi-stage infection cycle that initiates with the attachment and invasion of bladder host cells, intracellular growth and finally the rupture of these infected bladder cells and release of bacteria. A notable proportion of the bacteria released from an infected bladder cell have a filamentous phenotype—where bacteria have continued to grow without dividing. It is thought that these bacterial filaments are associated with their survival and persistence in the urinary tract.
The exact conditions that trigger filamentation during UTI are not known; however preliminary studies have suggested that a component of concentrated urine (>1.020 g/ml) triggers bacterial filamentation when UPEC are part of a biofilm (as occurs in UTI). In order to identify these urine factors, we have further developed the in vitro cell culture model of bladder cell infection by UPEC. By establishing infections in microfluidic chambers that allow real-time microscopic visualisation of infections, parameters such as bladder cell permeability and the extent of bacterial filamentation may be simultaneously observed and related to the progress of the infection.
Initially we looked at the effect of concentrated synthetic urine and observed that this failed to trigger bacterial filamentation. This suggested that it is components of real urine that triggers this filamentation. Next, we filtered real urine to remove macromolecules (>3 kDa), and observed extensive bacterial filamentation in the infection model, ruling out a macromolecular component as the key factor that triggers filamentation. Further investigation to identify the specific factor(s) that are responsible for triggering bacterial filamentation in UTI is underway.