Klebsiella variicola is a gram-negative bacterium belonging to the Enterobacteriaceae family. First identified in 2004, it is closely related to Klebsiella pneumoniae. While it can exist harmlessly in various environments and within the human body, K. variicola is recognized as an opportunistic pathogen capable of causing human infections.
Natural Habitats and Reservoirs
K. variicola is found in diverse ecological niches. It naturally occurs in soil and water, contributing to nutrient cycling. It also associates with various plants, including banana trees, sugarcane, rice, and corn, often fixing nitrogen.
The bacterium has also been isolated from the fungal gardens of leaf-cutter ants, where it supports colony growth through symbiotic nitrogen fixation. K. variicola also colonizes the human body as a commensal organism. It commonly resides in the gastrointestinal tract and can be present on the skin of healthy individuals without causing disease.
Sources of Human Infection
While K. variicola can reside harmlessly, it can become an infectious agent when conditions favor its proliferation and invasion. Human infections occur through direct contact, such as touching a cut on their skin with contaminated hands.
Infections can be hospital-acquired (nosocomial) or community-acquired. Hospital settings are common sites for transmission, often involving contaminated medical devices such as catheters, ventilators, and intravenous tubes. Healthcare workers can also inadvertently spread the bacteria if proper hand hygiene is not consistently followed.
Infections primarily affect individuals with compromised immune systems, pre-existing health conditions, or those undergoing invasive medical procedures. Risk factors include advanced age, chronic liver disease, diabetes, cancer, and kidney failure. Patients who have received prolonged antibiotic treatment or are hospitalized, particularly in intensive care or neonatal units, also face an increased risk of K. variicola infections.
Clinical Manifestations
Klebsiella variicola can cause various infections affecting different organ systems. Bloodstream infections (bacteremia or sepsis) are serious and linked to significant mortality. Symptoms often include fever, chills, rapid heart rate, and low blood pressure.
Urinary tract infections (UTIs) are another common infection caused by K. variicola, particularly in hospitalized patients with urinary catheters. These infections can lead to symptoms such as painful urination, frequent urges to urinate, and abdominal discomfort. If left untreated, UTIs can become life-threatening, especially in individuals with serious underlying illnesses.
The bacterium can also cause pneumonia, particularly hospital-acquired forms, leading to destructive changes in lung tissue. Patients may experience symptoms like fever, cough, and shortness of breath, sometimes producing thick, bloody sputum. Intra-abdominal infections, such as liver abscesses, have also been reported. These can present with abdominal pain, nausea, vomiting, fever, and chills.
Diagnosis and Treatment Considerations
Diagnosis of a Klebsiella variicola infection is confirmed through laboratory cultures of samples from the infected site. This may include blood, urine, sputum, or other body fluids, depending on the suspected infection type. Accurate identification of K. variicola can be challenging due to its close genetic resemblance to Klebsiella pneumoniae, sometimes leading to misidentification by standard biochemical tests. Advanced methods, such as MALDI-TOF mass spectrometry and gene sequencing, are more effective for precise differentiation.
Antibiotics are the primary treatment for K. variicola infections. A challenge in managing these infections is the bacterium’s capacity to develop antibiotic resistance. While K. variicola is intrinsically resistant to ampicillin, it can acquire resistance to a broad range of other antibiotics, including extended-spectrum beta-lactamases (ESBL) and carbapenemases.
Antibiotic susceptibility testing is routinely performed on isolated strains to guide appropriate treatment choices. This testing helps clinicians select effective antimicrobial agents, as treatment options for multidrug-resistant strains can be limited. Public health concerns are growing due to the emergence and spread of multidrug-resistant K. variicola strains, which can complicate clinical management and potentially lead to outbreaks.