What Are Urease Positive Bacteria and Their Health Risks?

While many bacteria are harmless or even beneficial, some possess specific tools that allow them to thrive in unique environments, sometimes at the expense of their host. One such group is the urease-positive bacteria, defined by their ability to produce an enzyme called urease. This capability has significant implications in medicine and environmental science, as it allows these microbes to alter their surroundings.

Understanding Urease and Its Activity

Urease is a nickel-containing enzyme that facilitates a specific chemical reaction: breaking down a common waste product called urea. When a bacterium produces this enzyme, it hydrolyzes urea into ammonia and carbon dioxide. This reaction fundamentally alters the local chemistry of the bacterial environment.

The production of ammonia is impactful because it is an alkaline substance. As ammonia accumulates, it raises the pH of its surroundings, making the environment less acidic. This ability to neutralize acid is a powerful survival mechanism for bacteria attempting to colonize acidic areas, such as the human stomach.

Key Urease Positive Bacteria and Their Environments

Several medically important bacteria are known for their urease activity, each adapted to a specific niche.

• Helicobacter pylori is associated with the stomach, where its urease production is fundamental to surviving the extremely acidic environment and colonizing the gastric mucosa.
• Proteus mirabilis is a frequent cause of urinary tract infections. It thrives in the urinary system, where its enzymatic activity has direct consequences for health.
• Klebsiella pneumoniae can inhabit both the respiratory and urinary tracts, showcasing its versatility as a pathogen.
• Ureaplasma urealyticum is commonly found in the urogenital tract of both men and women.

Beyond the human body, some urease-producing bacteria are also found in soil, where they participate in the nitrogen cycle by breaking down urea from animal waste.

Health Consequences of Urease Positive Bacteria

The urease enzyme is a direct contributor to how certain bacteria cause disease. The ammonia generated through its activity is toxic to human cells and can trigger inflammation. This mechanism is a primary virulence factor that can lead to significant health issues.

For Helicobacter pylori, neutralizing stomach acid allows the bacterium to establish a foothold in the gastric lining. This colonization can lead to chronic inflammation (gastritis), which may progress to more severe conditions like peptic ulcers. The long-term presence of H. pylori and the associated inflammation are also a recognized risk factor for developing stomach cancer.

Proteus mirabilis uses urease to cause problems in the urinary tract. The resulting increase in urine pH causes minerals like magnesium and phosphate to crystallize from the urine. These crystals can aggregate to form large struvite kidney stones, which can obstruct urine flow, cause severe pain, and complicate infections by providing a surface for bacteria to colonize.

Identifying Urease Activity in Bacteria

In clinical and laboratory settings, several reliable methods are used to determine if a bacterium is urease-positive. These tests are important for diagnosing infections caused by organisms like H. pylori. The tests work by detecting byproducts of the urease reaction, most commonly ammonia, which indicates the enzyme’s presence.

One common method is the rapid urease test (RUT), often performed during an endoscopy to check for H. pylori. A small tissue sample from the stomach lining is placed in a medium containing urea and a pH indicator. If urease is present, the breakdown of urea produces ammonia, causing a pH increase that results in a distinct color change.

The urea breath test is a non-invasive alternative where a patient ingests a special urea solution. If H. pylori is present, the urease breaks down the urea. A labeled form of carbon dioxide is then detected in the patient’s exhaled breath.

For bacteria grown in a lab, culture-based tests like Christensen’s urea agar are used. The bacterial sample is introduced to a sterile agar slant containing urea and a pH-sensitive dye. A urease-positive organism will break down the urea and produce ammonia, changing the color of the agar to a bright pink or magenta.