Klebsiella species are a group of bacteria widespread in nature that are significant pathogens in clinical settings. These organisms are classified as Gram-negative rods, meaning they do not retain the purple crystal violet stain during laboratory testing due to their cell wall structure. While often harmless in their natural environments, certain species can cause serious infections, particularly among vulnerable patients. They are a notable concern in hospitals and long-term care facilities, where they are a common cause of healthcare-associated infections.
Defining Klebsiella and Its Natural Habitat
Klebsiella bacteria are ubiquitous, found across various environments, including soil, surface waters, and vegetation. They are also a normal part of the human gut microbiota, residing in the gastrointestinal tract without causing disease in healthy individuals. In this state, the bacteria are considered commensal organisms.
The most medically relevant species is Klebsiella pneumoniae, frequently isolated from both clinical and environmental sources. Problems arise when this opportunistic organism moves from the gut to sterile sites within the body. This migration, often facilitated by a weakened immune system or medical procedures, allows the bacteria to act as a pathogen. While other species like K. oxytoca and K. aerogenes cause human infections, K. pneumoniae is the primary source of severe disease.
Common Infections Associated with Klebsiella
When Klebsiella species cause infection, the clinical manifestations can be severe and affect multiple organ systems. A primary concern is pneumonia, often acquired in a healthcare setting and referred to as ventilator-associated pneumonia (VAP) when affecting patients on mechanical ventilation. Klebsiella pneumonia is frequently destructive, characterized by thick, bloody sputum and a high mortality rate that can approach 50% even with treatment.
The bacteria are also a common cause of urinary tract infections (UTIs), particularly in hospitalized patients with indwelling catheters. These devices provide a pathway for the bacteria to enter the urinary tract. Klebsiella can also lead to bloodstream infections, known as bacteremia or sepsis, which is a life-threatening condition occurring when the bacteria spread throughout the body. Patients with chronic conditions like diabetes, cancer, dialysis, or organ transplants are at a higher risk of developing these severe infections.
The Issue of Antibiotic Resistance
The greatest threat posed by Klebsiella species is their ability to develop and share resistance to multiple types of antibiotics. This resistance has classified many strains as multi-drug resistant organisms (MDROs), severely limiting treatment options. The emergence of these resistant strains is a major public health concern because it leads to treatment failure, prolonged hospital stays, and increased mortality.
Resistance often occurs through the acquisition of mobile genetic elements, such as plasmids, which can be shared with other bacteria via horizontal gene transfer. These plasmids carry genes that encode for resistance enzymes, most notably the carbapenemases. Carbapenems are a class of last-resort antibiotics used to treat infections resistant to nearly all other drugs.
Bacteria that produce these enzymes are known as Carbapenem-resistant Klebsiella pneumoniae (CRKP). The enzyme, such as K. pneumoniae carbapenemase (KPC), chemically breaks down the carbapenem antibiotic, rendering it ineffective. Other resistance mechanisms involve the loss of outer membrane channels (porins) or the over-expression of efflux pumps, which prevent the antibiotic from reaching its target. Infections caused by CRKP strains are associated with higher mortality rates than those caused by susceptible strains.
Prevention and Transmission Control
Controlling the spread of Klebsiella involves strict adherence to hygiene and infection control protocols, especially within healthcare environments. Proper hand hygiene is the most effective measure to prevent transmission, as the bacteria can be spread on the contaminated hands of healthcare personnel. This practice requires washing hands before and after contact with patients and after touching hospital surfaces.
Hospitals must also focus on minimizing the use of invasive medical devices, such as urinary catheters and ventilators, and removing them as soon as they are no longer necessary. Contaminated medical equipment, including respiratory support devices, requires rigorous cleaning and sterilization procedures. For patients infected with highly resistant strains like CRKP, contact isolation protocols are implemented, typically involving the use of gowns and gloves. Proactive surveillance of high-risk units helps identify and contain potential outbreaks.