In vitroassays for clinical isolates of sequence type 131Escherichia colido not recapitulatein vivoinfectivity using a murine model of urinary tract infection

Abstract

AbstractSequence Type 131 isolates are a major cause of cystitis and pyelonephritis. Many studies rely solely onin vitroassays to screen for bacterial virulence factors associated with the pathogenicity of clinical isolates ofE. coli. Few studies have comparedin vitrofindings toin vivoinfectivity of clinical isolates. The purpose of this study was to evaluate the correlation betweenin vitroassays with the ability to cause cystitis and pyelonephritis in a murine model of urinary tract infection.In vitroassays were conducted according to published protocols and included: motility assays, biofilm formation, epithelial cell adhesion and invasion, and curli production. Twenty-one UPEC isolates ofE. coliST131 and non-ST131 were used for bothin vivoandin vitrostudies. Six mice per isolate were inoculated via urethral catheterization. CFUs were determined from bladder and kidneys.In vitroandin vivocorrelations were evaluated by multiple linear regression analysis. Pairwise linear regressions showed trendlines with weak positive correlations for motility, adhesion, and invasion and weak negative correlations for hemagglutination, biofilm and curli production. The ability ofE. coliST131 and non-ST131 clinical isolates to cause cystitis and pyelonephritis varies among strains. The R2Pearson Correlation value was less than ±0.5 for any pair, indicating little to no statistical association betweenin vitroandin vivofindings. These data showin vitrodata are not predictive of the ability of ST131E. colito infect and/or cause disease in a mouse model.Author summaryUrinary tract infections affect 150 million people annually andE. coliST131 have become the pandemic strain responsible for a majority of UTI, cystitis, and pyelonephritis cases. How ST131E. colihave become such prolific strain still remains to be elucidated. When evaluating bacterial pathogenicity, it is customary practice to usein vitroassays to predict isolate virulence and mechanisms of fitness, due to the lower cost, and relative ease of experimentation compared to more costly and complicatedin vivomodels. It is also common to use model organisms like pathogenicE. coliCFT073 or non-pathogenic lab strains such as BW25113 as representatives for the entire species. However, our research has shown that not only are model organisms substantially different from clinical isolates of ST131E. coli, butin vitroassays are poor predictors of clinical isolates’ ability to cause infection in a murine model of UTI. As such, research into the mechanisms of fitness for ST131 infectivity need to veer away from studying only model organisms and focus on utilizing pathogenic clinical isolates in conditions that more closely recapitulate urinary tract environmental niches.