Always getting cystitis? It could be because your urine's too acidic

June 29, 2015  15:36

Scientists have discovered why some people are more prone to painful urinary tract infections such as cystitis.

They say the acidity of a person's urine may influence how well bacteria can grow in the urinary tract, enabling it to flourish. 

Diet may also play a role, in the way that small waste molecules of food are converted by bacteria in the intestine before being excreted through urine.

The research, done at Washington University School of Medicine in St. Louis, may have implications for treating urinary tract infections, which are among the most common bacterial infections worldwide. 

Urinary tract infections (UTIs) often are caused by a strain of bacteria called Escherichia coli (E. coli).

Typical symptoms include a pain or a burning sensation when urinating, a need to urinate often and pain in the lower abdomen. 

Doctors have long relied on antibiotics to kill the microbes.

But increasing bacterial resistance to these drugs is leading researchers to look for alternative treatment strategies.

'Many physicians can tell you that they see patients who are particularly susceptible to urinary tract infections,' said senior author Jeffrey Henderson, assistant professor of medicine.

'We often don't know why certain people seem to be prone to recurrent UTIs.

'For a long time, we had inexpensive antibiotics that worked really well for this. But over the last 10-15 years, we have seen a huge jump in bacterial infections that are resistant to many of these drugs.'

With this in mind, Professor Henderson and his team were interested in studying how the body naturally fights bacterial infections.

They cultured E. coli in urine samples from healthy volunteers and noted major differences in how well different people's urine could make use of a key protein to limit bacterial growth.

They then divided these urine samples into two groups based on whether they had allowed or stopped bacterial growth.

The samples that had stopped the growth of bacteria were then analysed in closer detail.

The urine samples that stopped bacteria from growing showed more action of a key protein which the body makes naturally in response to infection.

In contrast, the samples that permitted bacteria to grow easily revealed less activity of this protein. 

The protein, called siderocalin, deprives bacteria of the iron it needs to grow.

The next step was to identify who, if anyone, had characteristics that made siderocalin more effective in the body.

'Age and gender did not turn out to be major players,' said study co-author Robin Shields-Cutler. 

'Of all the factors we measured, the only one that was really different between the two groups was pH - how acidic the urine was.'

Until now, it had been thought that acidic urine was a good thing, as it restricted bacterial growth.

But this study revealed urine that was less acidic - and closer to the neutral pH of pure water - showed higher activity of the protein siderocalin.

This, in turn, made it better at restricting bacterial growth than the more acidic samples.

The study was published in the Journal of Biological Chemistry.

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