Reducing the incidence of bacteriuria with or without symptoms in the vitamin C group was one of the secondary outcomes of a double-blind, randomized, controlled trial. The prevalence of bacteriuria in the vitamin C group was considerably lower than in the placebo group. Patients in both groups received trimethoprim/sulfamethoxazole as prophylaxis of Pneumocystis jiroveci pneumonia. It is also useful to some extent in the prevention of urinary tract infections . Also, patients in this center receive ceftriaxone as long as they have a urinary catheter. Despite these common antibiotic treatments, the prevalence of bacteriuria during first hospitalization after kidney transplantation was 60% in the placebo group.
UTI accounts for about half of all post-kidney transplant infections . The inhibitory impact of vitamin C on the growth of some pathogens like Escherichia coli, Pseudomonas aeruginosa, Klebsiella pneumonia, and Staphylococcus saprophyticus has been shown in some studies [7, 8].
The growing rate of antibiotic resistance in urinary tract pathogens has led to the search for non-antibiotic prophylaxis which is not affected by antibiotic resistance . In a study published in 2012 cranberry juice, l-methionine, or both modalities significantly reduced the annual incidence of UTI among kidney transplant recipients with recurrent UTIs compared to the year before the onset of prophylaxis . Information on the administration of a bacterial antigen vaccine for the prevention of UTI is advancing, but this type of treatment has been further studied in non-transplant patients with recurrent UTI [10, 11]. Since these interventions have not been studied in large population, they are not currently recommended .
Urinary acidification and production of reactive nitrogen species are proposed mechanisms for the effect of vitamin C on reducing urinary tract infections . Based on in vitro data, nitrite that is produced by bacteria can be reduced to nitric oxide and other nitrogen-reactive intermediates in the presence of vitamin C. These nitrogen intermediates have bactericidal effects [8, 12]. Vitamin C can also prevent biofilm formation on the urethral catheter surface. Besides, at the concentration of 80 to 100 mg/ml, vitamin C exerts an inhibitory effect on a preformed biofilm on the catheters . These desired urinary concentrations can only be achievable by administration of high-dose intravenous vitamin C . On the other hand, in another study, vitamin C could reduce adhesion of uropathogens to the silicone rubber and their colonization in the urine at the dose of 1 g/day for three consecutive days .
Some risk factors make the kidney transplant recipients more susceptible to UTI. These risk factors include female gender, older age, pre-transplant history of UTI, urinary reflux or polycystic kidney disease, long duration of urinary catheterization, and delayed allograft function [2, 9]. There was no difference regarding these risk factors between patients in the vitamin C and placebo groups in the present study. For further research, designing clinical trials with large sample size by controlling these risk factors between placebo and vitamin C groups is recommended. It is also suggested to differentiate between asymptomatic bacteriuria and UTI. Besides, recording urine pH at specified intervals may also be useful in the determination of the mechanism of action of vitamin C on bacteriuria and UTI.