Urease-producing bacteria

Antibiotics with activity against urease-producing bacteria, such as neomycin [42], paromomycin [44] or metronidazole [45], also reduce the production of intestinal ammonia and have proved to be of value. Vancomycin has also been used in patients with lactulose-resistant chronic encephalopathy [46]. The efficacy of neomycin is similar to that of lactulose [42]. However, a small percentage of this drug is absorbed from the gastrointestinal tract and may cause ototoxic and nephrotoxic effects, especially with continuous use over several months [47]. This drug should be used with particular caution by patients with renal insufficiency. The efficacy of metronidazole for... 

Neomycin and metronidazole both inhibit urease-producing bacteria and are useful, but their longterm use is limited by toxicity. 

Inhibiting the activity of urease-producing bacteria by using neomycin, metronidazole, or vancomycin can decrease production of ammonia. Neomycin at doses of 2 to 8 g daily in divided oral doses results in clinical improvement in as many as 80% of patients. At these doses, however, absorption is 1% to 5% and can result in irreversible ototoxicity and nephrotoxicity. As such, even though efficacy is equivalent to lactulose, neomycin should not be first-line therapy. Metronidazole produces response rates similar to neomycin, but side effects, particularly gastrointestinal, limit its use. In patients... 

Acetohydroxamic acid (250 mg p.o. t.i.d.), an antiurolithic agent, is indicated as an adjunctive agent in treating chronic urinary tract infections caused by urease-producing bacteria. Acetohydroxamic acid, which inhibits urease and reduces the production of ammonia, is devoid of antibacterial activity. 

The reduction of intestinal ammonia synthesis can also be achieved by the administration of non-absorbable disaccharides-like lactulose and lactitol or antibiotics like neomycin, paramomycin, metronidazole or rifaximin. Lactulose exerts several effects (1). acidification of the intestinal content resulting in a reduction of ammonia absorption and net movement of ammonia from the blood into the bowel and (2). reduced bacterial production of ammonia in the colonic lumen due to environmental changes with promotion of the growth of non-urease producing bacteria and (3). the cathartic effect. The daily dose of lactulose is between 30 and 60 g per day. The goal is to obtain 2-3 soft bowel movements per day. Recently lactulose has been proven to be effective even in patients with minimal HE (Prasad et al., 2007). 

An elevated ammonia concentration can be the result of primary or secondary defect of the urea cycle. Ammonia is mainly a by-product of amino acid metabolism, although it is also produced by intestinal urease-positive bacteria. The urea cycle converts ammonia (or ammonium, NH, ) to urea, which is excreted by the renal systan in order to keep the serum concentration of ammonia low. An impairment of the urea cycle results in... 

Corthesy, B., Boris, S., Isler, P., Grangette, C., and Mercenier, A. (2005), Oral imunization of mice with lactic acid bacteria producing Helicobacter pylori urease B subunit partially protects against challenge with Helicobacter felis,/. Infect. Dis., 192,1441-1449. 

Bacterial urease. A major source of ammonia in liver (approximately 25%) is produced by the action of certain bacteria in the intestine that possess the enzyme urease. Urea present in the blood circulating through the lower digestive tract diffuses across cell membranes and into the intestinal lumen. Once urea is hydrolyzed by bacterial urease to form ammonia, the latter substance diffuses back into the blood, which transports it to the liver. 

This reaction is one that you may have observed if you have a cat Urea is a waste product of the breakdown of proteins and is removed from the body in urine. Bacteria in kitty litter produce urease. As the urease breaks down the urea in the cat urine, the ammonia released produces the distinctive odor of an untended litter box. 

Urea is not cleaved by human enzymes. However, bacteria, including those in the human digestive tract, can cleave urea to ammonia and CO2, using the enzyme urease. Urease is not produced by humans. 

Helicobacter pylori have several flagella at one end, and they move in the mucus. These bacteria are chemotactic toward urea and carbonic anion. Helicobacter pylori can produce energy for movement by converting urea to ammonia via urease. Ammonia helps also to neutrahze the acidic condition nearby. Fmthermore, chemotaxis to carbonic anions helps these bacteria to stick to the stomach. 

The next group of multimembrane systems comprises membranes sensitized biologically using immobilized enzymes or microorganisms. Species that are directly sensed by an ISE are produced in the enzymatic reaction of the analyte. Examples of such sensors are those used for determination of urea in milk, based on immobilized urease and measurement of a pH change. An example of the application of bacteria strains is the use of immobilized recombinant Escherichia coli coupled with a pH electrode. Such electrodes have been used for determination of cephalosporins. When this bacterial strain is coupled with a CO2 gas sensor, glutamic acid determination can be carried out. 

Because they contain urease in their cells, many bacteria can hydrolyse urea, either derived as outlined above, or produced as an animal excretory product. 

An important property of enzymes is that they are specific that is. one enzyme can usually catalyze only one type of reaction. For example, a protease hydrolyzes only bonds between specific amino acids in proteins, an amylase works on bonds between glucose molecules in starch, and lipase attacks fats, degrading them to fatty acids and glycerol. Con.sequently, unwanted products are ea.sily controlled in enzyme-catalyzed reactions. Enzymes are produced only by living organisms, and commercial enzymes are generally produced by bacteria. Enzymes u.sually work (i.e., catalyze reactions) under mild conditions pH 4 to 9 and temperatures 75°F to 160°F. Most enzymes are named in terms of the reactions they catalyze. It is a customary practice to add the suffix -ase to a major pan of the name of the substrate on which the enzyme acts. For example, the enzyme that catalyzes the decomposition of urea is urease and the enzyme that attacks tyrosine is tyrosina.se. However. 

The urea-urease reaction is an enzyme-catalysed hydrolysis of urea, that produces ammonia and carbon dioxide according to the overall stoichiometry (1). This reaction occurs in numerous cellular systems, for example it is used by bacteria H. pylori in order to raise the local pH to protect itself from the harsh acidic environment of the stomach [6]. 

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