Differential Impact of Antibiotics on Various Adhesion Patterns of E.coli

Background: Urinary tract infections (UTIs) represent a significant global health challenge, with high recurrence rates underscoring the limitations of therapeutic strategies focused solely on genetic antibiotic resistance. This study investigates a critical, yet underappreciated, survival mechanism in Escherichia coli. Its capacity for phenotypic adaptation into protected morphological states and its utilization of the host epithelium as a defensive niche Methods: This study employed a human bladder epithelial cell line (UTI 5637) to model infection with a diverse panel of E.coli strains. Bacterial adhesion patterns were characterized via fluorescence microscopy after propidium iodide staining. Antibiotic susceptibility was determined using broth microdilution to establish minimum inhibitory concentrations (MIC). A comparative assay evaluated bacterial survival across three physiological states (planktonic, supernatant, and adherent) under antibiotic exposure, while assessing how adhesion phenotypes influenced antibiotic susceptibility. Bacterial viability was quantified via colony-forming units (CFU), and IC₅₀ values were calculated by linear interpolation from CFU counts across antibiotic concentrations. Statistical differences in IC₅₀ values across five adhesion phenotypes (Clumpy, Microcolonies, Chain, Diffuse, and Single) were assessed using one-way ANOVA with Tukey's HSD post-hoc test for each antibiotic. Statistical significance for environmental comparisons (adhered vs. planktonic and adhered vs. supernatant) was determined using independent t-tests, with significance denoted as *p < 0.05, **p < 0.01, and ***p < 0.001. Results: Investigation of host-pathogen interactions revealed five distinct adhesion morphotypes: Clumpy aggregates, Microcolonies, Chains, Diffuse forms, and Single cells. A consistent and statistically significant hierarchy of bacterial survival was established across all antibiotic treatments: Adherent populations demonstrated superior survival over supernatant fractions, which in turn proved more resilient than their planktonic counterparts (p < 0.05). Furthermore, the minimum concentration required for complete bacterial eradication consistently exceeded established clinical breakpoints by 2- to 8-fold. Phenotype-specific analysis revealed significant differences in IC₅₀ values across all five morphotypes (one-way ANOVA, p < 0.05 for all antibiotics). The Clumpy phenotype exhibited broad-spectrum resistance, with 7.3-fold higher tolerance to Meropenem (p = 0.017), 2.6-fold higher to Colistin (p = 0.0079), and 1.4-fold higher to Ciprofloxacin (p < 0.001). Microcolonies and Chains demonstrated extreme selective resistance to Tigecycline (29.0-fold, p = 0.0465 and 28.8-fold, p = 0.0474, respectively). The Diffuse phenotype showed paradoxical behavior—most resistant to Cefotaxime (3.5-fold, p = 0.0046) yet most sensitive to Colistin and Tigecycline. Single cells remained uniformly susceptible across all antibiotics. The most profound level of protection was observed when these robust phenotypes coexisted within the adherent environment, creating a synergistic effect that substantially diminished the efficacy of even last-resort antibiotic. Conclusion: Our findings establish that the interplay between bacterial phenotypic plasticity and the host-cell environment is a fundamental determinant of antibiotic treatment failure. These results identify a critical deficiency in standard susceptibility testing and underscore the necessity for novel therapeutic approaches capable of targeting these resilient, host-associated bacterial communities to effectively combat recurrent UTIs.