UTI and Bacterial Pods: The Invasion of the Bladder Snatchers*
Abstract & Commentary
Synopsis: Experiments suggest that bacteria may persist within bladder epithelial cells in a biofilm contained within pods, thus accounting for bacterial persistence manifested as chronic or recurrent urinary tract infection.
Source: Anderson GG, et al. Intracellular bacterial biofilm-like pods in urinary tract infections. Science. 2003;301:105-107.
Anderson and colleagues at the Washington University School of Medicine in St. Louis examined the experimentally acutely infected urinary bladders of immunodeficient mice. In mice infected with uropathogenic strains of Escherichia coli, they observed numerous large protrusions they termed pods on the bladder surface. These pods proved to contain bacteria embedded in a fibrous polysaccharide-rich matrix within the cytoplasm of bladder epithelial cells. The bacteria-matrix complex was surrounded by a "protective shell" of uroplakin.
Comment by Stan Deresinski, MD, FACP
Uropathogenic E coli initiate the first stage of infection upon binding to bladder epithelial cells. This binding is mediated by the FimH adhesin located at the tip of the bacterial type 1 pilus. This event initiates an inflammatory response mediated by the innate immune system, a significant event being the recognition of bacterial lipopolysaccharide by the Toll-like receptor 4-CD14 pathway. One result is the exfoliation into the urine of superficial epithelial cells, along with the bound and invading bacteria. Replication of the bacteria within the epithelial cells is associated with large numbers of organisms in the urine. Murine experiments by this same group have demonstrated that bacteria persist in this intracellular site, even in the face of antibiotic administration.
The experiments discussed here appear to provide an explanation for this recalcitrant behavior, with the intracellular bacteria enmeshed in a fibrous matrix within a uroplakin shell manifested as pods causing bulges in the epithelial surface. Uroplakin is a membrane protein that forms impermeable "plaques" on the luminal surface of the epithelial cell lining of the bladder. The polysaccharide matrix resembles a glycocalyx and, thus, the organism appears to be growing in an intracytoplasmic biofilm. Organisms growing in biofilm exhibit increased resistance to antimicrobials, as well as to host defenses. In this case, the biofilm is also surrounded by an impermeable shell in its intracellular position.
This is truly a novel finding, but it has so far been demonstrated only in mice. Confirmation of this finding in humans will be necessary. In addition, Anderson et al suggest the possibility that pods may play a role in other chronic or recurrent infections.
*In the movie "The Invasion of the Body Snatchers" aliens duplicated humans in large structures that looked like huge bean pods.
Dr. Derenski is Clinical Professor of Medicine, Stanford; Associate Chief of Infectious Diseases, Santa Clara Valley Medical Center.
Suggested Reading
1. Wullt B, et al. The host response to urinary tract infection. Infect Dis Clin North Am. 2003;17:279-301.
2. Johnson JR. Microbial virulence determinants and the pathogenesis of urinary tract infection. Infect Dis Clin North Am. 2003;17:261-278.
Experiments suggest that bacteria may persist within bladder epithelial cells in a biofilm contained within pods, thus accounting for bacterial persistence manifested as chronic or recurrent urinary tract infection.You have reached your article limit for the month. Subscribe now to access this article plus other member-only content.
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