Bacterial evolution of urinary tract infections acquired in the community and in the hospital. A case of Mexico

Introduction: Since “nothing in biology makes sense except in the light of evolution” (Dobzhansky T) and it develops through the interrelationships between living beings and their environment; the biological factors in the etiology of human infections can only be explained based on Darwin’s evolutionary theory. In this sense, environment as different as communities and hospitals originate diverse evolutionary processes in the causal agents of community and nosocomial infections; mainly in the development of resistance to antimicrobials. Methods: To validate the possible significant qualitative and quantitative differences between the causal agents of nosocomial and community-acquired urinary tract infections, and their respective antimicrobial resistances; a clinical-epidemiological, descriptive, transversal, comparative and retrospective study was conducted; based on every urine culture and antibiogram performed during a one-year period in a family medicine unit and a regional general hospital in Chihuahua, Mexico. For verification of the statistical significance of these differences, χ2, odds ratio, confidence interval and p-value were calculated with a 95% reliability limits for all cases. Results: Qualitative differences (genera, species and strains) were verified between the 27 causal agents of nosocomial and community urinary tract infections; with the most evolved bacteria and yeasts located in the hospital, having a 1.9 times higher resistance against almost every antibiotic, especially for Gram-negative bacteria and Escherichia coli. In all cases, these differences were statistically significant. For Gram-positive bacteria, less resistant in general, community strains had a 1.2 times higher resistance for two of four types of antimicrobials; but not significantly. Conclusion: Regarding antimicrobial sensitivity, important differences were evidenced as for the clinical practice guides recommendations; based on research from environments, societies and medical attention quite different from Mexico. Even if bacterial evolutionary processes and antibiotic resistance are global, they do not run in parallel nor are contemporary everywhere; and although similarities eventually prevail, they occur with local peculiarities; therefore, their consideration is decisive for a suitable and effective prevention and therapy of infectious diseases and their epidemic outbreaks.