Bacterial Persistence in Isolated and Recurrent Urinary Tract Infection in Postmenopausal Population

Objectives: Recurrent urinary tract infection (rUTI), with an estimated incidence of 10-15%, occurs more frequently in postmenopausal women²-³. Persister cells, which enter a dormant state during antibiotic exposure, may play a role in rUTI⁴. The aim of this study was to quantify and compare the bacterial persister phenotype in urine collected from postmenopausal women with isolated acute UTI (aUTI) and rUTI.

Methods: Urine from postmenopausal women with aUTI (N = 10) or rUTIs (n = 30) were utilized. Women were diagnosed with aUTI if they had no prior UTI in the preceding 12 months and rUTI if they have had > 3 culture proven ( > 10⁵ CFU uropathogen) in the past 12 months or > 2 culture proven UTI in the past 6 months. Specimens were plated on Lysogeny Broth agar, cultured overnight, and standardized to a concentration of 0.05 optical density (600 nm). The minimum inhibitory concentration (MIC) of antibiotics -- nitrofurantoin, trimethoprim-sulfamethoxazole (bactrim), ofloxacin, and fosfomycin -- for each isolate was measured according to CLSI Method⁶. Isolates were treated with each antibiotic at the MIC, washed, and resuspended to generate persister cells. To quantify bacterial growth, each dilution was plated in quadruplicate to determine colony forming units per mL (CFU/mL).⁷ The entire experimental process was repeated in triplicate. Data was analyzed for significance (p < 0.05) using a two-way ANOVA with multiple comparisons followed by Tukey test in Prism 9.3.0.

Results: Participant characteristics are listed in Table 1. Women with aUTI were similar to women with rUTI except those with aUTI were more likely to be obese (50% vs. 27%, p < 0.05) and hypertensive (80% vs. 60%, p< 0.05). The persister cell phenotype was demonstrated in all E. coli isolates treated with each antibiotic in both groups (Figure 1). After treatment with bactrim, nitrofurantoin, and ofloxacin, urine from women with rUTIs demonstrated significantly less growth of the persister cell phenotype compared to women with aUTI (p < 0.05). Treatment with fosfomycin similarly reduced the persister cell phenotype in both groups compared to vehicle control (p < 0.01) but there was no difference between groups.

Conclusions: This study demonstrated in vitro bacterial persistence of E. coli isolates obtained from women with either an aUTI or rUTI. Paradoxically, we found urine from women with rUTIs generated less bacterial persistence than women with aUTI except after treatment with fosfomycin. Persister cells, alone, may not be sufficient to distinguish mechanisms of rUTI in postmenopausal women. Further study is needed to understand the interplay between bacterial persistence and resistance.