Corynebacterium urinary tract infections (UTIs) present a unique clinical challenge because they differ significantly from common UTIs, which are typically caused by the gram-negative bacterium Escherichia coli. Corynebacterium species are gram-positive organisms often overlooked as contaminants rather than true pathogens. This oversight is problematic, as infection with certain species can lead to a specific, severe urinary tract disease requiring specialized attention and distinct treatment protocols.
Corynebacterium Species and Patient Risk Factors
The species most frequently implicated in severe Corynebacterium UTIs is Corynebacterium urealyticum. This organism is a slow-growing, lipophilic, and multi-drug resistant bacterium. C. urealyticum is distinguished by its strong urease activity, which drives the specific pathology seen in these infections.
This bacterium is an opportunistic pathogen, typically causing disease in individuals with compromised defenses. Patients with underlying structural abnormalities of the urinary tract or those who have recently undergone urologic procedures are particularly susceptible. Prolonged hospitalization and the use of indwelling urinary catheters significantly increase the risk, making the infection often nosocomial (hospital-acquired).
Immunosuppressed patients, such as transplant recipients or those on cytotoxic drugs, are also at high risk. The use of broad-spectrum antibiotics, which can disrupt the body’s normal microbial balance, is another risk factor.
How the Infection Causes Damage
The unique mechanism by which C. urealyticum causes damage centers on its production of the enzyme urease. This enzyme acts on urea, breaking it down into ammonia and carbon dioxide. The resulting ammonia significantly alkalinizes the urine, rapidly increasing the pH to levels that can reach 8.0 or 9.0.
This highly alkaline environment drastically changes the chemical composition of the urine, leading to supersaturation with magnesium, ammonium, and phosphate ions. This facilitates the precipitation of a mineral compound known as struvite. Struvite then forms stones and calcified encrustations on the lining of the urinary tract and on foreign bodies like catheters.
The formation of these stones is the hallmark of C. urealyticum infection, leading to alkaline encrusted cystitis or pyelitis. These calcified plaques can reduce bladder capacity, cause chronic inflammation, and lead to obstruction of the urinary tract, potentially resulting in severe kidney damage or renal failure. The stones also serve as a protected niche for the bacteria, shielding them from the host’s immune response and antibiotic therapy.
Laboratory Identification and Diagnostic Challenges
Diagnosing a Corynebacterium UTI presents several difficulties for the standard clinical laboratory. C. urealyticum is a fastidious, slow-growing organism. In routine urine cultures, typically incubated for 18 to 24 hours, the organism often fails to produce colonies large enough to be noticed. This slow growth frequently causes the infection to be missed or dismissed as a negative culture.
Corynebacterium species are common colonizers of the skin, meaning they can easily contaminate a urine sample during collection. Since they are frequently found as part of the normal skin flora, laboratory personnel may mistakenly identify the organism as a non-pathogenic contaminant, or “diphtheroid.” This challenge is compounded because the organism grows best on enriched media and may require an extended incubation period of 48 to 72 hours for proper isolation.
Clinical suspicion is important to prompt the specific laboratory requests needed for identification. A strong indicator is the presence of highly alkaline urine (pH greater than 7.0) in a patient with UTI symptoms, which should immediately suggest the involvement of a strong urease-producing organism. The detection of struvite crystals (crystalluria) in the urine sediment also provides a clue. When these clinical signs are present, the laboratory must be specifically requested to hold the culture plates for longer periods or to use specialized identification methods, such as biochemical panels or mass spectrometry, to confirm the species.
Clinical Management and Treatment Protocols
The management of C. urealyticum UTIs is complex and requires a dual approach: targeted antibiotic therapy and removal of calcified material. The bacterium is multi-drug resistant, often showing resistance to many common UTI antibiotics, including beta-lactams, trimethoprim-sulfamethoxazole, and aminoglycosides. This resistance pattern makes empiric treatment challenging and often unsuccessful.
The most reliable antimicrobial agents against C. urealyticum are the glycopeptides, specifically vancomycin and teicoplanin, to which the isolates are generally susceptible. Fluoroquinolones and rifampin are also sometimes used, but susceptibility can vary, making antibiotic sensitivity testing a necessity. Treatment duration is often prolonged, lasting between 14 to 30 days for complicated cases.
Antibiotic therapy alone is often insufficient for a cure due to the presence of struvite stones and encrustations. These calcified deposits harbor the bacteria and physically block the antibiotics from reaching the infection site. Surgical or endoscopic intervention, such as lithotripsy or percutaneous nephrostolithotomy, to remove the stones and encrusted plaques is often required. Urinary acidification may also be employed alongside antibiotics to inhibit the urease activity and slow down stone formation.