Citrobacter amalonaticus
Jeff Nye

Citrobacter amalonaticus are Gram-negative, rod-shaped bacteria that are aerotolerant anaerobes. C. amalonaticus are chemoheterotrophs and use citrate as their sole carbon source. They can be found in the human digestive system and have been linked to some minor digestive issues like diarrhea. C. amalonaticus can also be an opportunistic pathogen, which means that they cause few problems in healthy individuals, but are capable of causing severe infections in someone with a weakened immune system.  The most common illness that C. amalonaticus causes is Urinary Tract Infections, which it can even do in a healthy host, this doesn’t normally happen, but it has a higher frequency than any other Citrobacter based infection. Citrobacter amalonaticus is normally found in the intestines, but if it manages to maintain a presence in the urinary tract, they will cause an infection, which is similar to most other urinary tract infections. Citrobacter amalonaticus has also been known to cause an illness similar enteric fever, this causing a discrepancy in the diagnosis of the illness because it hasn’t been known to do this, but has now had a few reported cases of the illness.  Another discrepancy is the commonness of Citrobacter amalonaticus; it is so common in human intestines that it is mostly screened out or disregarded when blood or stool tests are run and it isn’t naturally pathogenic.

Bacteria inhabit almost any space available and C. amalonaticus is no exception.  It is found in the soil, air, water, and even the intestines of several animals including humans and bats.  In bats, it has been discovered that C. amalonaticus is capable of breaking down chitin from partial digested insects.  This is an important relationship because no known vertebrate naturally has the enzymes to break down the chitin that is found in their insect heavy diets.  Without C. amalonaticus or similar bacteria, the harder portions of the insects, like the legs and wings, would just pass through the digestive system mostly undigested.  This is usually the case anyways, but some bats keep their last few insect meals from autumn in their intestines and store the harder chitinous parts over the winter to be digested using the bacterial enzymes and provide food without hunting since many insects wouldn’t be available to hunt due to the cold weather. 

C. amalonaticus also has the ability to accumulate metals from its environment by combining them with phosphates.  When C. amalonaticus has organic phosphates available, it is able to break them down and use the phosphate to attract metal ions that are in its environment even if they are in very small concentrations.  It is capable of collecting massive amounts of metal phosphates and isn’t restricted by becoming saturated; it has been shown that one gram of C. amalonaticus is able to collect about nine grams of uranyl phosphate from its environment when given a day and the proper phosphates that it needs.  This ability makes C. amalonaticus very useful because it could be used to remove uranium or other harmful materials from contaminated water or soil and the uranyl phosphate crystals can then be removed and the bacteria can keep cleaning.


Suwansrinon, Kanitta, Henry Wilde, Visith Sitprija, and Rekha Hanvesakul. "Enteric Fever-like Illness Caused by Infection with Citrobacter Amalonaticus." J Med Assoc Thai 88.6 (2005): 837-40. Medical Association Thai. Queen Saovabha Memorial Institute, Thai Red Cross Society, 06 Nov. 2005. Web. 17 Feb. 2010. <>.

Chitinase in Insectivorous Bats
John O. Whitaker, Jr., H. Kathleen Dannelly and David A. Prentice.  Journal of Mammalogy, Vol. 85, No. 1 (Feb., 2004), pp. 15-18 Published by: American Society of Mammalogists  Stable URL:

Macaskie, L. E., R. M. Empson, A. K. Cheetham, C. P. Grey, and A. J. Skarnulis. 1992. Uranium bioaccumulation by a Citrobacter sp. as a result of enzymatically mediated growth of polycrystalline HUO2PO4. Science 257:782-784

"Citrobacter." Dorlands Medical Dictionary. Merck, 2007. Web. 17 Feb. 2010. <>

*Disclaimer - This report was written by a student participaring in a microbiology course at the Missouri University of Science and Technology. The accuracy of the contents of this report is not guaranteed and it is recommended that you seek additional sources of information to verify the contents.


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