Treatment of rUTI, defined as ≥ 3 episodes of uncomplicated, symptomatic UTI within 12 months or 2 episodes within 6 months [1], can be challenging in postmenopausal women. One treatment option is bladder instillation, which includes exposing the bladder to an antimicrobial solution to remove the planktonic bacteria. The cationic detergent, Cetylpyridinium chloride (CPC), used in oral rinses to treat gingivitis [2], may be a promising antimicrobial candidate for use in bladder instillation. A preliminary limited trail in women with antibiotic refractory rUTI using 0.05% CPC for bladder instillation indicates CPC as a safe therapeutic option but the patients reported mild symptoms of bladder irritation. At a high concentration of 0.05%, CPC inhibits bacterial growth but may also cause exfoliation of bladder epithelial cells. To reduce potential side effects of bladder irritation during CPC instillation we sought to identify the minimal inhibitory concentration (MIC) of CPC against diverse uropathogenic bacteria. We hypothesize that CPC will have broad-spectrum activity against diverse uropathogenic species. The goal of this study is to design an optimal CPC instillation strategy for women with rUTI. We aim to determine the minimum inhibitory and bactericidal concentrations (MIC/MBCs) for CPC in diverse uropathogenic bacteria.

The MIC for CPC was determined using the previously described Broth Microdilution method (REF), wherein serial dilutions of CPC were inoculated with a fixed number of bacterial cells in a microtiter plate, and growth inhibition was measured. Phylogenetically diverse uropathogens including four Escherichia coli (UPEC) strains, two of Enterococcus faecalis and Klebsiella pneumoniae strains, recently isolated from the urine of women with recurrent urinary tract infection, were used as test strains. Commensal E. coli K-12 W3110, and UPEC strain UTI89, were used as reference strains. E. coli ATCC 25922, which is commonly used in MIC testing for cationic peptides, was used a quality control strain. Assays were performed in Mueller Hinton Broth (MHB) in ambient conditions using overnight bacterial cultures normalized to OD600 of 0.05. A two-fold dilution series of CPC was prepared in MHB ranging from 0.00003% - 0.013%. Bacteria were inoculated in each well containing the CPC dilutions to a final concentration of 4x105 colony-forming units (CFU)/mL. Growth control and sterility control wells were included. After 16 - 20 hours of static incubation at 37°C, growth inhibition was measured. The MIC was recorded as the lowest concentration of CPC for which no visible growth of the tested isolate was observed. 
The MBC was determined by spotting 10 uL from wells where no growth was observed onto Mueller Hinton Agar plates. After 16 - 20 hours of incubation at 37°C, the plates were examined for growth, and the concentration for which no growth occurred was recorded as the MBC for the test isolate.

The MIC and MBC for CPC ranges from 0.0008 to 0.0016 % for UPEC isolates. For K. pneumoniae isolates, the MIC and MBC ranges from 0.0031 – 0.0016 %. Whereas, for E. faecalis isolates, the MIC of CPC is 0.0002% and MBC is 0.004%.

Patients enrolled in the preliminary limited trial of 0.05% CPC bladder instillation reported mild symptoms of bladder irritation. At a high concentration of 0.05%, CPC is likely causing lysis of both bacterial and bladder epithelial cells. Using Broth Microdilution assay, we determined CPC concentration as low as 0.0063% is bactericidal against all tested uropathogens. Future trials of bladder instillation could be performed using 0.0063% CPC which might help in alleviating the symptoms of bladder irritation.

The cationic detergent, Cetylpyridinium chloride, is effective against diverse uropathogenic species. At a low concentration of 0.0063%, CPC shows bactericidal activity towards all tested uropathogens. Future work will focus on studying the CPC pharmacodynamics using time-kill kinetic assay to determine the rate at which CPC effectively kills uropathogenic bacteria. To mitigate the side-effects of bladder irritation and inflammation, we also aim to study the cytotoxic effects of CPC against bladder epithelial cells.

Hussain, Syed A, Alhalabi, Feras, and Zimmern, Philippe E. “Long-Term Efficacy of Fulguration of Trigonitis for Recurrent Urinary Tract Infections in Women.” Urological Science 26.3 (2015): 197–201.
Fei Teng Tao He Shi Huang Cun-Pei Bo Zhen Li Jin-Lan Chang Ji-Quan Liu Duane Charbonneau Jian Xu Rui Li Jun-Qi Ling. “Cetylpyridinium Chloride Mouth Rinses Alleviate Experimental Gingivitis by Inhibiting Dental Plaque Maturation.” International Journal of Oral Science 8(3) Springer Nature B.V (2016): pp. 182–90.