Klebsiella is a type of Gram-negative bacteria commonly found in various environments, including soil, water, plants, and the human body. These rod-shaped bacteria often have a protective polysaccharide capsule. While they can be part of the normal flora in areas like the human nose, mouth, and gastrointestinal tract, they can also act as opportunistic pathogens, causing a range of infections when they spread to other parts of the body.
Common Klebsiella Species
The genus Klebsiella includes several species, with some being more commonly associated with human infections than others. Klebsiella pneumoniae stands out as the most frequently encountered species in clinical settings, known for causing diverse infections in humans. This bacterium is a non-motile, encapsulated, lactose-fermenting, facultative anaerobe that appears as mucoid colonies on agar plates. It is closely related to Klebsiella oxytoca, which is distinguished by being indole-positive and performing lactose fermentation.
Klebsiella aerogenes, previously known as Enterobacter aerogenes, is another species that can cause opportunistic infections. While generally found in the human gastrointestinal tract without causing disease in healthy individuals, it can lead to infections in immunocompromised patients. K. aerogenes is approximately 1 to 3 microns in length and is capable of motility via peritrichous flagella.
Klebsiella granulomatis, formerly known as Calymmatobacterium granulomatis, is a distinct species known for causing granuloma inguinale, also called donovanosis, a sexually transmitted infection. This bacterium is a non-motile, aerobic bacillus, typically measuring 0.5 to 2.0 µm, with a non-sporulated capsule. It is biochemically characterized as catalase-positive, phenylalanine deaminase-negative, citrate test-positive, and urease-positive.
Where Klebsiella Resides
Klebsiella bacteria are widely distributed in nature, found in soil, water, and on plants. In humans and animals, Klebsiella species are routinely present as part of the normal flora, particularly in the nose, mouth, and gastrointestinal tract.
Klebsiella is also prevalent in healthcare settings, including hospitals and nursing homes. In these environments, the bacteria can colonize medical equipment and surfaces, contributing to their spread. Their presence in healthcare facilities makes them a concern for healthcare-associated infections.
Infections Associated with Klebsiella
Pneumonia is a common infection caused by Klebsiella, especially in hospital settings. This form of pneumonia can result in symptoms such as fever, chills, coughing, and the production of thick, sometimes bloody, mucus, often described as “currant jelly sputum.”
Urinary tract infections (UTIs) are another frequent manifestation of Klebsiella infection, particularly in healthcare environments. These infections occur when the bacteria enter the urinary tract, which can happen, for example, with the use of urinary catheters. Symptoms of Klebsiella UTIs are similar to those caused by other bacteria, including frequency, urgency, painful urination, and lower back pain.
Klebsiella can also lead to bloodstream infections, known as bacteremia or sepsis. These infections can originate from a localized infection spreading to the blood or directly infecting the bloodstream, causing symptoms like fever, chills, and shaking. Surgical site and wound infections are also possible if the bacteria enter through a break in the skin, such as from injury or surgery.
More severe or less common infections include liver abscesses and meningitis. Klebsiella pneumoniae liver abscesses can sometimes lead to metastatic infections, spreading to other sites like the central nervous system, causing meningitis. Meningitis caused by Klebsiella can present with high fever, headaches, and a stiff neck.
The Challenge of Antibiotic Resistance
Antibiotic resistance is a concern in the management of Klebsiella infections. Klebsiella species, particularly Klebsiella pneumoniae, have developed mechanisms to resist multiple antibiotics, making treatment challenging. This resistance involves the production of enzymes that inactivate antibiotics.
Extended-spectrum beta-lactamase (ESBL) producing Klebsiella strains are resistant to many commonly used antibiotics, including most penicillins and cephalosporins. These enzymes break down the beta-lactam ring structure common to these antibiotics, rendering them ineffective. While ESBL-producing strains remain susceptible to carbapenems, the emergence of carbapenem-resistant Klebsiella (CRKP) presents a serious challenge.
CRKP strains, sometimes referred to as “superbugs,” are resistant to carbapenems, which are last-resort antibiotics for severe bacterial infections. The primary mechanism for carbapenem resistance in Klebsiella is the production of carbapenemase enzymes. The increasing prevalence of these resistant strains means that infections can be more difficult to treat, potentially leading to longer hospital stays, increased morbidity, and higher mortality rates.