Antibacterial effects of nitrite in urine

Urinary tract infections (UTI`s) are among the most common conditions causing individuals to seek medical care. In addition, catheter-associated infections account for most of the hospital-acquired UTI´s and is also a major source of resistant nosocomial pathogens. The majority of bacterial strains causing UTI have a nitrate-reducing capacity and since the 1920s, when the urinary nitrite test was first developed, this dipstick assay has been an important component of modern UTI diagnosis.

In this thesis we have expanded the role of nitrite beyond diagnosis of infection and explored its role as an antimicrobial agent. From earlier studies it is known that acidification of nitrite results in the formation of nitric oxide (NO) and other reactive nitrogen oxides, which are toxic to a variety of microorganisms.

The aim of the present thesis was to investigate NO formation and possible antibacterial effects of acidified nitrite-containing urine. We also sought to determine the antibacterial effect of a two-step procedure in which bacteria were first fed with nitrate to form nitrite, followed later by acidification of the urine. Finally we wanted to evaluate in vitro a novel concept for intravesical delivery of antibacterial NO via the retention balloon of a urinary catheter. NO formation was measured in headspace gas using a chemiluminiscence-technique, while antibacterial effects were evaluated by turbidity measurements and by viable counts.

We show that large amounts of the antimicrobial gas NO are generated in mildly acidified nitrite-containing human urine and this NO formation is greatly enhanced by the addition of ascorbic acid. Furthermore, we show that mildly acidified nitrite-containing human urine has potent antimicrobial activity against three of the most common urinary pathogens and this inhibitory effect is further increased by ascorbic acid.

We also found, that Escherichia coli self destructs when it is first allowed to generate nitrite and then transferred to mildly acidified urine. Translated into clinical terms, this could imply that ingestion of nitrate followed some hours later by acidification of urine could be a new approach for treatment of UTI. Finally, potent antibacterial effects were also observed in infected urine when the nitrite-derived nitrogen oxides were delivered via the retention balloon of a urinary catheter.

In conclusion, we describe potent antibacterial effects of acidified nitrite-containing urine and also suggest a novel attractive alternative to prevent catheter-associated urinary tract infections.

List of scientific papers

I. Lundberg JO, Carlsson S, Engstrand L, Morcos E, Wiklund NP, Weitzberg E (1997). Urinary nitrite: more than a marker of infection. Urology. 50(2): 189-91.
https://doi.org/10.1016/S0090-4295(97)00257-4

II. Carlsson S, Wiklund NP, Engstrand L, Weitzberg E, Lundberg JO (2001). Effects of pH, nitrite, and ascorbic acid on nonenzymatic nitric oxide generation and bacterial growth in urine. Nitric Oxide. 5(6): 580-6.
https://doi.org/10.1006/niox.2001.0371

III. Carlsson S, Govoni M, Wiklund NP, Weitzberg E, Lundberg JO (2003). In vitro evaluation of a new treatment for urinary tract infections caused by nitrate-reducing bacteria. Antimicrob Agents Chemother. 47(12): 3713-8.
https://doi.org/10.1128/AAC.47.12.3713-3718.2003

IV. Carlsson S, Weitzberg E, Wiklund NP, Lundberg JO (2005). Intravesical nitric oxide delivery for prevention of catheter-associated urinary tract infections. Antimicrob Agents Chemother. [Accepted]
https://doi.org/10.1128/AAC.49.6.2352-2355.2005