Urinary tract infections (UTIs) occur when microbes colonize the urinary system. While Escherichia coli is the most common cause, other organisms can also be responsible. One such organism is Klebsiella pneumoniae, a type of Gram-negative bacteria that can cause a spectrum of infections, including UTIs. Understanding the biology and prevalence of Klebsiella helps explain why these UTIs are often viewed differently from standard infections.
Prevalence of Klebsiella in Urinary Tract Infections
Klebsiella pneumoniae is widely recognized as one of the most common causes of bacterial UTIs after E. coli, which typically accounts for 75–90% of cases in community settings. Globally, Klebsiella is frequently the second or third most prevalent pathogen isolated from urine cultures. Studies have estimated that Klebsiella species are responsible for approximately 5–15% of all UTIs.
The prevalence of Klebsiella UTIs shows a distinct difference between community-acquired and hospital-acquired infections. In community-acquired cases, Klebsiella accounts for a smaller fraction of infections. However, in hospital-acquired or healthcare-associated UTIs, its proportion significantly increases. For instance, in catheter-associated UTIs, Klebsiella can account for as much as 11% of cases, positioning it as a major pathogen in clinical environments.
Distinct Features of Klebsiella
The features of Klebsiella make its UTIs more difficult to manage than those caused by other bacteria. A defining feature of K. pneumoniae is its thick polysaccharide capsule, an outer layer that acts as a protective shield. This capsule makes it harder for the host’s immune system to clear the bacteria and can also impede the penetration of some antibiotics.
Klebsiella pneumoniae also has a strong ability to form biofilms, which are complex communities of bacteria encased in a self-produced matrix. This formation is particularly problematic on medical devices, such as indwelling urinary catheters, where the bacteria can colonize the surface. Bacteria within these biofilms are shielded from both immune responses and antibiotic treatments, leading to persistent and recurrent infections. The presence of hypervirulent strains of K. pneumoniae means these variants are more likely to cause severe, invasive diseases even in relatively healthy individuals.
Specific Risk Factors for Klebsiella UTIs
Klebsiella UTIs primarily affect individuals whose defenses are compromised or who have specific environmental exposures. The greatest risk factor is exposure to a healthcare setting, including recent hospitalization, admission to an intensive care unit, or residence in a long-term care facility. These environments often select for more resistant strains of the bacteria.
Patients with indwelling urinary catheters are at a high risk of developing a Klebsiella Catheter-Associated UTI (CAUTI). The duration of catheterization is directly correlated with the likelihood of infection. Other underlying health conditions also increase susceptibility, such as diabetes, chronic lung disease, and immunocompromised states. These factors, combined with exposure to invasive medical devices, create an environment where K. pneumoniae can thrive and cause infection.
Treatment and Managing Antibiotic Resistance
Treating a Klebsiella UTI begins with identifying the specific strain and its susceptibility to antibiotics, a process known as culture and susceptibility testing. Initial treatment for uncomplicated cases may involve common oral antibiotics, but the emergence of resistant strains has complicated this approach. The primary challenge is the high prevalence of Multi-Drug Resistance (MDR) in K. pneumoniae isolates, particularly in healthcare settings.
Many strains produce enzymes that break down common antibiotics, most notably Extended-Spectrum Beta-Lactamases (ESBLs). These ESBL-producing strains are resistant to many penicillins and cephalosporins, often requiring the use of carbapenems. For severe infections caused by ESBL-producing Klebsiella outside of the urinary tract, carbapenems remain the preferred first-line treatment.
Even more concerning is the rise of Carbapenem-Resistant Enterobacteriaceae (CRE) strains, which are resistant even to carbapenems. These infections require specialized, often intravenous, antibiotics like ceftazidime-avibactam or meropenem-vaborbactam, agents designed to overcome these resistance mechanisms. For uncomplicated cystitis caused by susceptible ESBL strains, oral agents like nitrofurantoin or trimethoprim-sulfamethoxazole may be effective if susceptibility is confirmed. Treatment choice is highly dependent on local resistance patterns and laboratory testing results.