Postdoc, Karolinska Institutet


I try to understand bacterial physiology in the context of severe urinary tract infections

Urinary tract infections (UTIs) are extremely common. Plus, they are recurrent, thereby imposing a huge burden to the health care system. Most UTIs are caused by a single bacterial species: uropathogenic Escherichia coli (UPEC). I am interested in understanding how UPEC physiology changes in function of and adapts to the dynamic changes in the tissue microenvironment. I am also interested in the ability of UPEC to colonize the host tissues by forming biofilms, bacterial 'citadels' in which bacterial cells are embedded in a protective matrix, thereby having an important survival advantage within the host. Indeed, bacteria can also colonize materials such as urinary catheters by forming biofilms. That is why most people undergoing renal dyalisis end up with an infection. Bacterial living in biofilms are up to 1,000 times more resistant to antibiotics, and they are a reason for the recurrence of UTIs. I hope that a better understanding of these fundamental processes will lead to a better-defined picture of the infection process itself and eventually to more selective treatments to complement (or ideally replace) the use of antibiotics. Normally UTIs 'ascend' from the urethra to the bladder (causing cystitis) up to the kidneys (causing pyelonephritis). During this ascending transit, bacteria face a a diverse, often changing tissue microenvironment, and they need to adapt their physiology readily to survive. Specifically, my current research focuses on anaerobic processes. Yes, bacteria can 'breathe' even when oxygen concentration is very low, as it is the case in some particular niches within the urinary tract. To do so, they just use other substances for cellular respiration instead of oxygen. Anaerobic respiration is possible thanks to specific enzymes called anaerobic terminal reductases. There is at least one for every substance bacteria are able to use for respiration. By knocking-out these pathways individually, we have discovered an inter-connection between biofilm formation and anaerobic respiration that we believe is important for bacterial colonization of tissues and materials. We have also found that bacterial cells lacking specific anaerobic pathways have an enormous fitness disadvantage in vivo. In other words, they are less able to cause infection. Our ongoing studies pursue to unravel the gene regulatory networks that are responsible for these promising results, to understand the 'hows' and 'whys' and find the way of using the patient's benefit.


Virulence Factors of Uropathogenic E. coli and Their Interaction with the Host

Abstract: Publication date: Available online 4 November 2014 Source:Advances in Microbial Physiology Author(s): Petra Lüthje , Annelie Brauner Urinary tract infections (UTIs) belong to the most common infectious diseases worldwide. The most frequently isolated pathogen from uncomplicated UTIs is Escherichia coli. To establish infection in the urinary tract, E. coli has to overcome several defence strategies of the host, including the urine flow, exfoliation of urothelial cells, endogenous antimicrobial factors and invading neutrophils. Thus, uropathogenic E. coli (UPEC) harbour a number of virulence and fitness factors enabling the bacterium to resist and overcome these different defence mechanisms. There is no particular factor which allows the identification of UPEC among the commensal faecal flora apart from the ability to enter the urinary tract and cause an infection. Many of potential virulence or fitness factors occur moreover with high redundancy. Fimbriae are inevitable for adherence to and invasion into the host cells; the type 1 pilus is an established virulence factor in UPEC and indispensable for successful infection of the urinary tract. Flagella and toxins promote bacterial dissemination, while different iron-acquisition systems allow bacterial survival in the iron-limited environment of the urinary tract. The immune response to UPEC is primarily mediated by toll-like receptors recognising lipopolysaccharide, flagella and other structures on the bacterial surface. UPEC have the capacity to subvert this immune response of the host by means of actively impacting on pro-inflammatory signalling pathways, or by physical masking of immunogenic structures. The large repertoire of bacterial virulence and fitness factors in combination with host-related differences results in a complex interaction between host and pathogen in the urinary tract.

Pub.: 20 Nov '14, Pinned: 31 Aug '17

The cytochrome bd-I respiratory oxidase augments survival of multidrug-resistant Escherichia coli during infection.

Abstract: Nitric oxide (NO) is a toxic free radical produced by neutrophils and macrophages in response to infection. Uropathogenic Escherichia coli (UPEC) induces a variety of defence mechanisms in response to NO, including direct NO detoxification (Hmp, NorVW, NrfA), iron-sulphur cluster repair (YtfE), and the expression of the NO-tolerant cytochrome bd-I respiratory oxidase (CydAB). The current study quantifies the relative contribution of these systems to UPEC growth and survival during infection. Loss of the flavohemoglobin Hmp and cytochrome bd-I elicit the greatest sensitivity to NO-mediated growth inhibition, whereas all but the periplasmic nitrite reductase NrfA provide protection against neutrophil killing and promote survival within activated macrophages. Intriguingly, the cytochrome bd-I respiratory oxidase was the only system that augmented UPEC survival in a mouse model after 2 days, suggesting that maintaining aerobic respiration under conditions of nitrosative stress is a key factor for host colonisation. These findings suggest that while UPEC have acquired a host of specialized mechanisms to evade nitrosative stresses, the cytochrome bd-I respiratory oxidase is the main contributor to NO tolerance and host colonisation under microaerobic conditions. This respiratory complex is therefore of major importance for the accumulation of high bacterial loads during infection of the urinary tract.

Pub.: 22 Oct '16, Pinned: 31 Aug '17

Bacterial virulence phenotypes of Escherichia coli and host susceptibility determine risk for urinary tract infections.

Abstract: Urinary tract infections (UTIs) are caused by uropathogenic Escherichia coli (UPEC) strains. In contrast to many enteric E. coli pathogroups, no genetic signature has been identified for UPEC strains. We conducted a high-resolution comparative genomic study using E. coli isolates collected from the urine of women suffering from frequent recurrent UTIs. These isolates were genetically diverse and varied in their urovirulence, that is, their ability to infect the bladder in a mouse model of cystitis. We found no set of genes, including previously defined putative urovirulence factors (PUFs), that were predictive of urovirulence. In addition, in some patients, the E. coli strain causing a recurrent UTI had fewer PUFs than the supplanted strain. In competitive experimental infections in mice, the supplanting strain was more efficient at colonizing the mouse bladder than the supplanted strain. Despite the lack of a clear genomic signature for urovirulence, comparative transcriptomic and phenotypic analyses revealed that the expression of key conserved functions during culture, such as motility and metabolism, could be used to predict subsequent colonization of the mouse bladder. Together, our findings suggest that UTI risk and outcome may be determined by complex interactions between host susceptibility and the urovirulence potential of diverse bacterial strains.

Pub.: 24 Mar '17, Pinned: 31 Aug '17