Zbl. Bakt. 277, 276-279 (1992) © Gustav Fischer Verlag, StuttgartlNew York
Editorial
The Urogenital Microbial Ecosystem GREGOR REID Associate Professor, Department of Microbiology and Immunology, University of Western Ontario, London, Ontario N6A 5B8, Canada and Associate Professor, Department of Surgery, University of Toronto, Ontario, Canada
Introduction Over the last 15 years, great strides have been made in understanding the pathogenesis of urinary tract infections (UTI), especially those caused by Escherichia coli in females. However, many questions remain, and one wonders to what extent acquired knowledge has impacted upon prevention or therapy. The incidence of the disease has not decreased by any significant amount, and it remains an important cause of morbidity amongst adult women and the elderly.
Therapeutic Approach It has been well established that bacterial adhesion to the uroepithelial surface forms an important phase in the infectious process (13). The determination that specific bacterial adhesins and host receptors are involved in the initial bacterial binding has led to the search, by many groups of investigators, for ways to inhibit adhesion. One mode of approach has been to develop a preventive therapy using bacterial adhesin components which would compete for receptor sites. The initial encouraging in vitro results have not as yet led to a commercial product. Why not? Perhaps there are many answers, but several points merit review. Firstly, from which of the many uropathogenic strains would a vaccine come, using which of many adhesin and surface components? For example, the E. coli P fimbrial antigen is not present on all uropathogens and its ability to confer adhesion and survival in the urinary tract has been questioned (1). In addition, the expression of P fimbriae appears to be associated with causation of pyelonephritis, a relatively rare disease. Therefore few patients would potentially henefit from the vaccine, even if it was successfully developed to the market. The concept has been explored that bacterial adhesion can be blocked by direct competition for a receptor site using fimbrial proteins, receptor molecules or antibodies. The question is, how much intervention is required to prevent infection? In order to solve this problem, we must know how much bacterial adhesion is required to induce infection. Unfortunately, this question has never been addressed, although an association between
The Urogenital Microbial Ecosystem
277
high adherence and virulence was one proposed (15). Clearly, the level of adhesion can vary amongst patients (9); a mean of five bacteria per bladder cell may result in significant infection (> 105 bacteria per ml urine), as can a mean of 80 bacteria per cell. Therefore, in some patients, the mere presence of adherent bacteria may be indicative of infection. Should a preventive measure block all adhesion to all cells, and if so can this be achieved? The answer likely is no; this cannot be achieved by administration of competing adhesins or receptors, and perhaps that is why products of this type are not available. To base a therapy on stimulating the immune system, it should be assumed that there is a correlation between UTI and a suppressed immune response. However, this remains to be established. At present, there are efforts being made to develop and test various vaccination processes, including the instillation of uropathogenic antigens into the genital tract (16). Time will tell if this succeeds in preventing infection, and if the basis for its action can be defined. It seems puzzling that this approach could protect the host, when uropathogenic organisms are present in the urogenital flora of patients with recurrent UTI, and these bacterial antigens do not appear to confer protection.
Emergence of Pathogens from the Urogenital Flora Whilst the ability of pathogens to cause disease has received much attention, the ability of these organisms to survive in and emerge from a diverse microbiological niche, has been largely ignored. For example, it has not been determined, how the organisms which infect the bladder pass transiently or establish themselves in the urogenital tract (vagina, perineum, urethra) and compete with other members of that flora? The importance of Lactobacillus species in protecting the host from infection has long been proposed. However, only recently has there been some indication that it could reduce the risk of recurrent UTI in selected groups of patients (2, 10). Likely, the lactobacilli are but one link in a chain. The hourly changes in the flora's contents, the impact which nutrients have on bacterial growth and metabolism, and the disruptive effects caused to the flora by antimicrobial agents (used in food substances and to treat infection), and spermicides, indicates the complexity of this ecosystem (7, 8, 10, 11, 14). The ability of E. coli, enterococci and other uropathogens to emerge from the urogenital flora and infect the bladder is still a matter of some conjecture. If effective preventive measures (other than broad spectrum killing of bacteria in the bladder) are to be introduced, a better understanding of the ecosystem's microbial content is required.
Biofilm Formation In complicated UTI, the infectious process is invariably related to the insertion of prostheses, blockage of urinary flow or other complications. The adhesion of bacteria to biomaterials and tissues has been demonstrated in vitro and in vivo, with the process being initiated by deposition of conditioning films on to the prosthesis or epithelial surface. After the bacteria adhere to the film/surface, they aggregate, multiply and form drug resistant biofilm (3, 4), which may be benign or infectious, depending upon the site and organisms involved. Recently, biofilm deposition was shown on bladder mucosal cells of asymptomatic spinal cord injured patients (12). The decision to defer therapy in asymptomatic UTI is invariably made to avoid emergence of drug resistence organisms, and because it is inevitable that reinfection will occur. In addition, the treatment of biofilms has been so ineffective that in many patients with an infected prosthesis, the device must be replaced. This failure is likely due to inadequate concentrations of antibiotics being selected from laboratory testing of
278
G.Reid
planktonic, rather than biofilm organisms. In addition, few antibiotics tested to date show the necessary penetration ability into biofilms (3). The use of avirulent organisms to colonize the bladder, in preference to virulent pathogens, has been tried with some success in Sweden (5). A similar approach in catheterized patients has not been reported. The question remains as to what damage is caused by bacteria which persist for long periods of time in the host?
Future Developments Where do we go from here? In the future, if scientist, clinicians and industry representatives work together, it is feasible that new diagnostic and treatment products will evolue. In ten years time, infections may be detected directly and quickly from bladder cell analyses, and antibiotics selected from biofilm elminination data as opposed to minimum inhibitory concentrations of planktonic organisms. Certainly, therapy should be modified or simplified and given for a short duration for patients with uncomplicated acute UTI. It is possible that a better understanding of the inflammatory response (for example, the secretion of interleukin-6 following bacterial stimulation by Gram-negative uropathogens (6)) in symptomatic and asymptomatic patients will lead to new approaches to therapy. If we are . content not to treast asymptomatic infection, perhaps products will be developed to negate symptoms in symptomatic patients. Prevention of recurrences may involve manipulation or supplementation of the patient's urogenital flora. Clinical follow-up may monitor the urogenital flora and the presence of bacterial by-products at systemic sites, with a view to lowering the risk of morbidity and mortality associated with recurrent UTI. Ther~ is surely no time like the present to channel the past efforts of researchers into practical applications.
Acknowledgements. This work was supported by a grant from the Medical Research Council of Canada. The input of Dr. Andrew W. Bruce is appreciated.
References
e. Svanborg: Persistence of Escherichia coli bacteriuria is not determined by bacterial adherence. Infect. Immun. 59 (1991) 2915-2921 Bruce, A. w., G. Reid,j.A. McGroarty, M. Taylor, and e. Preston: Preliminary study on the prevention of recurrent urinary tract infection in adult women using intravaginal lactobacilli. Int. Urogynecol. J. 3 (1992) 22-25 Costerton, j. w., K.-]. Cheng, G.G. Geesey, T.!. Ladd, j.e. Nickel, M. Dasgupta, and T.]. Marrie: Bacterial biofilms in nature and disease. Ann. Rev. Microbiol. 41 (1987) 435-464 Gristina, A. G.: Biomaterial-centered infection: microbial adhesion versus tissue integration. Science 237 (1987) 1588-1595 Hagberg, L., A. W. Bruce, G. Reid, e. Svanborg Eden, K. Lincoln, and G. Lidin-Janson: Colonization of the urinary tract with live bacteria from the normal fecal and urethral flora in patients with recurrent symptomatic urinary tract infections. In: Host-parasite interactions in urinary tract infections (E. H. Kass and e. Svanborg Eden, eds.), pp. 194-197. University of Chicago Press, Chicago (1989) Hedges, S., M. Svensson, and C. Svanborg: Interleukin-6 response of epithelial cell lines to bacterial stimulation in vitro. Infect. Immun. 60 (1992) 1295-1301 Hooton, T.M., c.L. Fennell, A.M. Clark, and W.E. Stamm: Nonoxynol-9: differential
1. Andersson, P., I. Engberg, G. Lidin-Janson, K. Lincoln, R. Hull, S. Hull, and
2. 3. 4. 5.
6. 7.
The Urogenital Microbial Ecosystem
279
antibacterial activity and enhancement of bacterial adherence to vaginal epithelial cells. Infect. Dis. 164 (1991) 1216-1219 8. McGroarty, J.A., S. Chong, G. Reid, and A. W. Bruce: Influence of the spermicidal compound nonoxynol-9 on the growth and adhesion of urogenital bacteria in vitro. Curro Microbiol. 21 (1990) 219-223 9. Reid, G. and H.J. L. Brooks: A fluorescent antibody staining technique to detect bacterial adherence to urinary tract epithelial cells. Stain Techno!. 60 (1985) 211-217 10. Reid, G., A. W. Bruce, J. A. McGroarty, K.-J. Cheng, and J. W. Costerton: Is there a role for lactobacilli in prevention of urogenital and intestinal infections? Clin. Microbiol. Rev. 3 (1990) 335-344 11. Reid, G., A. W. Bruce, R. L. Cook, and M. Llano: Effect on the urogenital flora of antibiotic therapy for urinary tract infection. Scand. J. Infect. Dis. 22 (1990) 43-47 12. Reid, G., R. Charbeneau-Smith, D. Lam, M. Lacert, Y.S. Kang, and K. Hayes: Bacterial biofilm formation in the urinary bladder of spinal cord injured patients. Paraplegia 30 (1992) 13. Reid, G and J. D. Sobel: Bacterial adherence in the pathogenesis of urinary tract infection: a review. Rev. Infect. Dis. 9 (1987) 470-487 14. Seddon, J. M., A. W. Bruce, P. Chadwick, and D. Carter: Introital bacterial flora - effect of increased frequency of micturition. Br. J. Uro!. 48 (1976) 211-218 15. Svanborg Eden, c., L.A. Hanson, U. Jodal, U. Lindberg, and A. Soh I Akerlund: Variable adherence to normal human urinary-tract epithelial cells of Escherichia coli strains associated with various forms of urinary-tract infections. Lancet i (1976) 490-492 16. Uehling, D. T., w.J. Hopkins, and E. Balish: Decreased immunologic responsiveness following intensified vaginal immunization against urinary tract infection. J. Urol. 143 (1990) 143-145
J.
Professor Gregor Reid, Office of Research Services, SLB 328, University of Western Ontario, London, Ontario, Canada N6A 5B8
Editorial
The Urogenital Microbial Ecosystem GREGOR REID Associate Professor, Department of Microbiology and Immunology, University of Western Ontario, London, Ontario N6A 5B8, Canada and Associate Professor, Department of Surgery, University of Toronto, Ontario, Canada
Introduction Over the last 15 years, great strides have been made in understanding the pathogenesis of urinary tract infections (UTI), especially those caused by Escherichia coli in females. However, many questions remain, and one wonders to what extent acquired knowledge has impacted upon prevention or therapy. The incidence of the disease has not decreased by any significant amount, and it remains an important cause of morbidity amongst adult women and the elderly.
Therapeutic Approach It has been well established that bacterial adhesion to the uroepithelial surface forms an important phase in the infectious process (13). The determination that specific bacterial adhesins and host receptors are involved in the initial bacterial binding has led to the search, by many groups of investigators, for ways to inhibit adhesion. One mode of approach has been to develop a preventive therapy using bacterial adhesin components which would compete for receptor sites. The initial encouraging in vitro results have not as yet led to a commercial product. Why not? Perhaps there are many answers, but several points merit review. Firstly, from which of the many uropathogenic strains would a vaccine come, using which of many adhesin and surface components? For example, the E. coli P fimbrial antigen is not present on all uropathogens and its ability to confer adhesion and survival in the urinary tract has been questioned (1). In addition, the expression of P fimbriae appears to be associated with causation of pyelonephritis, a relatively rare disease. Therefore few patients would potentially henefit from the vaccine, even if it was successfully developed to the market. The concept has been explored that bacterial adhesion can be blocked by direct competition for a receptor site using fimbrial proteins, receptor molecules or antibodies. The question is, how much intervention is required to prevent infection? In order to solve this problem, we must know how much bacterial adhesion is required to induce infection. Unfortunately, this question has never been addressed, although an association between
The Urogenital Microbial Ecosystem
277
high adherence and virulence was one proposed (15). Clearly, the level of adhesion can vary amongst patients (9); a mean of five bacteria per bladder cell may result in significant infection (> 105 bacteria per ml urine), as can a mean of 80 bacteria per cell. Therefore, in some patients, the mere presence of adherent bacteria may be indicative of infection. Should a preventive measure block all adhesion to all cells, and if so can this be achieved? The answer likely is no; this cannot be achieved by administration of competing adhesins or receptors, and perhaps that is why products of this type are not available. To base a therapy on stimulating the immune system, it should be assumed that there is a correlation between UTI and a suppressed immune response. However, this remains to be established. At present, there are efforts being made to develop and test various vaccination processes, including the instillation of uropathogenic antigens into the genital tract (16). Time will tell if this succeeds in preventing infection, and if the basis for its action can be defined. It seems puzzling that this approach could protect the host, when uropathogenic organisms are present in the urogenital flora of patients with recurrent UTI, and these bacterial antigens do not appear to confer protection.
Emergence of Pathogens from the Urogenital Flora Whilst the ability of pathogens to cause disease has received much attention, the ability of these organisms to survive in and emerge from a diverse microbiological niche, has been largely ignored. For example, it has not been determined, how the organisms which infect the bladder pass transiently or establish themselves in the urogenital tract (vagina, perineum, urethra) and compete with other members of that flora? The importance of Lactobacillus species in protecting the host from infection has long been proposed. However, only recently has there been some indication that it could reduce the risk of recurrent UTI in selected groups of patients (2, 10). Likely, the lactobacilli are but one link in a chain. The hourly changes in the flora's contents, the impact which nutrients have on bacterial growth and metabolism, and the disruptive effects caused to the flora by antimicrobial agents (used in food substances and to treat infection), and spermicides, indicates the complexity of this ecosystem (7, 8, 10, 11, 14). The ability of E. coli, enterococci and other uropathogens to emerge from the urogenital flora and infect the bladder is still a matter of some conjecture. If effective preventive measures (other than broad spectrum killing of bacteria in the bladder) are to be introduced, a better understanding of the ecosystem's microbial content is required.
Biofilm Formation In complicated UTI, the infectious process is invariably related to the insertion of prostheses, blockage of urinary flow or other complications. The adhesion of bacteria to biomaterials and tissues has been demonstrated in vitro and in vivo, with the process being initiated by deposition of conditioning films on to the prosthesis or epithelial surface. After the bacteria adhere to the film/surface, they aggregate, multiply and form drug resistant biofilm (3, 4), which may be benign or infectious, depending upon the site and organisms involved. Recently, biofilm deposition was shown on bladder mucosal cells of asymptomatic spinal cord injured patients (12). The decision to defer therapy in asymptomatic UTI is invariably made to avoid emergence of drug resistence organisms, and because it is inevitable that reinfection will occur. In addition, the treatment of biofilms has been so ineffective that in many patients with an infected prosthesis, the device must be replaced. This failure is likely due to inadequate concentrations of antibiotics being selected from laboratory testing of
278
G.Reid
planktonic, rather than biofilm organisms. In addition, few antibiotics tested to date show the necessary penetration ability into biofilms (3). The use of avirulent organisms to colonize the bladder, in preference to virulent pathogens, has been tried with some success in Sweden (5). A similar approach in catheterized patients has not been reported. The question remains as to what damage is caused by bacteria which persist for long periods of time in the host?
Future Developments Where do we go from here? In the future, if scientist, clinicians and industry representatives work together, it is feasible that new diagnostic and treatment products will evolue. In ten years time, infections may be detected directly and quickly from bladder cell analyses, and antibiotics selected from biofilm elminination data as opposed to minimum inhibitory concentrations of planktonic organisms. Certainly, therapy should be modified or simplified and given for a short duration for patients with uncomplicated acute UTI. It is possible that a better understanding of the inflammatory response (for example, the secretion of interleukin-6 following bacterial stimulation by Gram-negative uropathogens (6)) in symptomatic and asymptomatic patients will lead to new approaches to therapy. If we are . content not to treast asymptomatic infection, perhaps products will be developed to negate symptoms in symptomatic patients. Prevention of recurrences may involve manipulation or supplementation of the patient's urogenital flora. Clinical follow-up may monitor the urogenital flora and the presence of bacterial by-products at systemic sites, with a view to lowering the risk of morbidity and mortality associated with recurrent UTI. Ther~ is surely no time like the present to channel the past efforts of researchers into practical applications.
Acknowledgements. This work was supported by a grant from the Medical Research Council of Canada. The input of Dr. Andrew W. Bruce is appreciated.
References
e. Svanborg: Persistence of Escherichia coli bacteriuria is not determined by bacterial adherence. Infect. Immun. 59 (1991) 2915-2921 Bruce, A. w., G. Reid,j.A. McGroarty, M. Taylor, and e. Preston: Preliminary study on the prevention of recurrent urinary tract infection in adult women using intravaginal lactobacilli. Int. Urogynecol. J. 3 (1992) 22-25 Costerton, j. w., K.-]. Cheng, G.G. Geesey, T.!. Ladd, j.e. Nickel, M. Dasgupta, and T.]. Marrie: Bacterial biofilms in nature and disease. Ann. Rev. Microbiol. 41 (1987) 435-464 Gristina, A. G.: Biomaterial-centered infection: microbial adhesion versus tissue integration. Science 237 (1987) 1588-1595 Hagberg, L., A. W. Bruce, G. Reid, e. Svanborg Eden, K. Lincoln, and G. Lidin-Janson: Colonization of the urinary tract with live bacteria from the normal fecal and urethral flora in patients with recurrent symptomatic urinary tract infections. In: Host-parasite interactions in urinary tract infections (E. H. Kass and e. Svanborg Eden, eds.), pp. 194-197. University of Chicago Press, Chicago (1989) Hedges, S., M. Svensson, and C. Svanborg: Interleukin-6 response of epithelial cell lines to bacterial stimulation in vitro. Infect. Immun. 60 (1992) 1295-1301 Hooton, T.M., c.L. Fennell, A.M. Clark, and W.E. Stamm: Nonoxynol-9: differential
1. Andersson, P., I. Engberg, G. Lidin-Janson, K. Lincoln, R. Hull, S. Hull, and
2. 3. 4. 5.
6. 7.
The Urogenital Microbial Ecosystem
279
antibacterial activity and enhancement of bacterial adherence to vaginal epithelial cells. Infect. Dis. 164 (1991) 1216-1219 8. McGroarty, J.A., S. Chong, G. Reid, and A. W. Bruce: Influence of the spermicidal compound nonoxynol-9 on the growth and adhesion of urogenital bacteria in vitro. Curro Microbiol. 21 (1990) 219-223 9. Reid, G. and H.J. L. Brooks: A fluorescent antibody staining technique to detect bacterial adherence to urinary tract epithelial cells. Stain Techno!. 60 (1985) 211-217 10. Reid, G., A. W. Bruce, J. A. McGroarty, K.-J. Cheng, and J. W. Costerton: Is there a role for lactobacilli in prevention of urogenital and intestinal infections? Clin. Microbiol. Rev. 3 (1990) 335-344 11. Reid, G., A. W. Bruce, R. L. Cook, and M. Llano: Effect on the urogenital flora of antibiotic therapy for urinary tract infection. Scand. J. Infect. Dis. 22 (1990) 43-47 12. Reid, G., R. Charbeneau-Smith, D. Lam, M. Lacert, Y.S. Kang, and K. Hayes: Bacterial biofilm formation in the urinary bladder of spinal cord injured patients. Paraplegia 30 (1992) 13. Reid, G and J. D. Sobel: Bacterial adherence in the pathogenesis of urinary tract infection: a review. Rev. Infect. Dis. 9 (1987) 470-487 14. Seddon, J. M., A. W. Bruce, P. Chadwick, and D. Carter: Introital bacterial flora - effect of increased frequency of micturition. Br. J. Uro!. 48 (1976) 211-218 15. Svanborg Eden, c., L.A. Hanson, U. Jodal, U. Lindberg, and A. Soh I Akerlund: Variable adherence to normal human urinary-tract epithelial cells of Escherichia coli strains associated with various forms of urinary-tract infections. Lancet i (1976) 490-492 16. Uehling, D. T., w.J. Hopkins, and E. Balish: Decreased immunologic responsiveness following intensified vaginal immunization against urinary tract infection. J. Urol. 143 (1990) 143-145
J.
Professor Gregor Reid, Office of Research Services, SLB 328, University of Western Ontario, London, Ontario, Canada N6A 5B8
