Chapter 20 : Integrated Pathophysiology of Pyelonephritis

The nephron. The nephron is the basic filtration unit of the kidney, composed of tubular and vascular elements. Arrows denote the direction of fluid flow.

Real-time, 2-photon microscopy of UPEC strain CFT073: GFP+ (LT004) infecting the proximal tubule. Epithelium of the infected tubule (blue) and blood flow (red) are outlined by fluorophore-labeled dextran. Micro-infused bacteria are visualized by genetically encoded GFP+ (green). A: Foci of infection 1 h post-infusion of LT004. Arrow points at bacteria adhering to the epithelium. B: Foci of infection 5 h post infusion. Massive green fluorescence indicates bacterial multiplication. C: Foci of infection 22 h post infusion. Lack of green fluorescence indicates clearance of bacteria. D: Non-infected renal tissue adjacent to the infection site shown in C. Scale bar = 30 µm. E: Ex vivo histological analysis of the foci of infection shown in C by confocal microscopy. Nuclear stain Hoechst 33342 (blue) and leukocyte marker α-CD18-Cy3 (red) have been added. Fluorophore-labeled dextran outlining the infected tubule is pseudocolored (yellow). Scale bar = 50 µm. F: Magnification of image E. The arrow highlights a neutrophil phagocytosing bacteria. Scale bar = 10 µm (From Månsson LE, et al. 2007. Real-time studies of the progression of bacterial infections and immediate tissue responses in live animals. Reprinted from Cell Microbiol ( 16 ), with permission.)

Epithelial-barrier disruption and impaired renal filtration due to UPEC infection. Real-time 2-photon imaging of the foci of infection 4 h post-infusion of UPEC strain LT004. Images obtained 7, 20, and 80 s after intravenous bolus infusion of fluorophore-labeled 10 kilodalton (kDa) dextran are shown (red). In the non-infected nephron (upper part of figure), efficient filtration is observed as the tubular appearance of the bright-red fluorescence arising from the labeled dextran (20 s) is followed by an obvious drop in intensity (80 s). This indicates renal clearance. Renal obstruction of the infected nephron (lower part of figure) is observed as only limited fluorescent dextran enters the tubule. Epithelial-barrier function is destroyed in the infected tubule, as dextran is observed to enter the epithelial layer (arrowhead, 7 s), suggestive of epithelial and endothelial dysfunction. In contrast, the healthy epithelia in the non-infected nephron exclude the dextran (arrowhead, 20 s). Vascular clotting can also be observed in the vasculature next to the infected nephron (arrow, 20 s). (From Melican K, et al. 2011. Uropathogenic E. coli P and type 1 fimbriae act in synergy in a living host to facilitate renal colonization leading to nephron obstruction. Reprinted from PLoS Pathog ( 14 ), with permission.)

Clot formation in mucosal infections. Real-time 2-photon imaging of a UPEC strain LT004 (green)-infected nephron (blue) shows platelets (arrow) in the form of black silhouettes surrounded by blood (red) within the peri-tubular vasculature, 2.5 h post-infection. Black masses adhered to the vessel wall (arrow head) suggest the presence of platelet aggregates. The high-intensity-red fluorescence indicates stagnant blood flow and a lack of red blood cell movement. Scale bar = 30 µm. (From Melican K, et al. 2008. Bacterial infection-mediated mucosal signaling induces local renal ischemia as a defence against sepsis. Reprinted from Cell Microbiol ( 17 ), with permission.)

Pathophysiogram of pyelonephritis illustrates how the microenvironment of infected tissue changes dynamically during infection (upper panel), and the associated changes relevant for bacterial growth (lower panel). Axis of each plot represents the degree of intensity and/or involvement (arbitrary units) of each defined trait during the time course of the infection.

Schematic representation of classical research disciplines that coalesce to form ‘tissue microbiology’, a recently proposed concept that integrates a range of disciplines and expertise. At the base of the pyramid are microbiology, which represents the in vitro study of microbial pathogens, and cellular biology, which focuses on the study of host cell types. Cellular microbiology was a discipline formed where microbiology and cellular biology overlapped. Coined in 1996, the approach was aimed at studying host–pathogen interactions using another’s perspectives, tools, and competences. Histology and physiology remained individual and required separate analysis. As knowledge and technological advancements make for unprecedented tools for intravital studies, tissue microbiology can now be established, advancing infection biology with an all-inclusive approach to generate an integrated view of the pathophysiology of infection.