Urinary tract infections (UTI) are one of the most common and costly infections worldwide. The primary cause of these infections is uropathogenic Escherichia coli (UPEC). UPEC undergo a multi-stage infection cycle that includes attachment and invasion of the bladder host cells, intracellular growth and finally bladder cell rupture and bacterial release. When released from the host cells, a notable proportion of bacteria have a filamentous phenotype – bacteria that have continued to grow without dividing. These filaments have been associated with the survival and persistence of the bacteria in the urinary tract.
The exact conditions that trigger filamentation during UTI are not known; however preliminary studies have suggested that a molecular component in concentrated urine may be required. In order to identify these factors, we have further developed the in vitro cell culture model of infection. We use flow cytometry and microscopy to measure the extent of bacterial filamentation during bladder cell infection. In addition, the infection can be directly monitored by real-time microscopy in a flow-chamber apparatus. Parameters such as bladder cell permeability are simultaneously observed and related to the progress of the infection.
To begin to narrow down the search for a molecular trigger of filamentation in UTI, we initially performed a simple fractionation of concentrated human urine, into large and small molecules (3000 Da cut-off). By exposing UPEC-infected bladder cells to these fractions, the results showed that filamentation occurred strongly in the presence of the small molecules but was completely absent in the presence of large molecules. Further investigation is underway, to identify the specific factor(s) that are responsible for triggering bacterial filamentation in UTI.