An international group of researchers from China, the US and the UK recently published a new study on the toxicity of melamine (CAS 108-78-1) in the scientific peer-reviewed journal Science Translational Medicine (Zheng et al. 2013). Melamine’s toxicity is related to kidney stones formed in the presence of cyanuric acid (CAS 108-80-5). Exposure to both melamine and cyanuric acid is of concern due to the increased risk for kidney stone formation. It was previously thought that cyanuric acid was solely an impurity of melamine. The new study now shows that cyanuric acid is produced by intestinal bacteria Klebsiella. This type of bacterium is assumed to be present in the gut microbiome of around 1% of the human population.

In their study, the researchers exposed rats to melamine in combination with an antibiotic or to melamine alone. Rats treated with melamine in combination with antibiotics lacked Klebsiella and did not exhibit cyanuric acid formation. When Klebsiella were present in rats exposed to melamine only, the risk of kidney stone formation was significantly increased. In addition, the formation of cyanuric acid by Klebsiella bacteria was confirmed in vitro.

The study’s authors state that “gut microbial activities can affect the metabolism and toxicity of food contaminants and pollutants and, therefore, should be taken into consideration in measuring the impact of human environmental exposure events.” In China in 2008, criminal practices led to the adulteration of milk with high levels of melamine. Presence of melamine-degrading bacteria in the guts of melamine exposed infants may have been the reason for several deaths. Melamine is used in food contact materials and migration into foods has been observed, albeit at levels far below those presently considered toxic (EFSA 2010).


Zheng, X., et al. (2013). “Melamine-Induced Renal Toxicity Is Mediated by the Gut Microbiota.” Science Translational Medicine 5(172): 172ra122.