Klebsiella aerogenes is a Gram-negative bacterium belonging to the family Enterobacteriaceae, a group commonly found in the intestines of humans and animals. This rod-shaped organism is classified as an opportunistic pathogen. It typically does not cause disease in healthy individuals but can become infectious when immune defenses are weakened. The bacterium is found in diverse locations, from the natural environment to the human body, providing multiple pathways for transmission and infection.
Natural Environmental Reservoirs
Klebsiella aerogenes is widely distributed outside of living hosts across various natural environments. The organism is commonly isolated from soil, where its ability to survive in diverse conditions allows it to thrive.
The bacterium is also frequently detected in aquatic ecosystems, including fresh surface waters and sewage systems. These water-based environments serve as dispersal routes, particularly when contaminated with animal or human waste. Furthermore, K. aerogenes has been identified on vegetation and plants, where it can act as a plant pathogen causing diseases like soft rot.
Human and Animal Colonization
The organism maintains a close association with living hosts by colonizing the gastrointestinal (GI) tract of both humans and warm-blooded animals. In these hosts, K. aerogenes exists as part of the normal gut flora without causing disease.
For humans, the GI tract is a significant source of the bacterium. This internal presence becomes a potential source of infection if the host experiences a decline in health or undergoes a medical procedure that breaches the body’s natural barriers. The bacterium can then transition from a harmless resident to an agent of disease, infecting sites outside the gut.
Presence in Healthcare Settings
K. aerogenes is prevalent in hospitals, long-term care facilities, and intensive care units (ICUs). In these settings, it transitions to a pathogen and is a major cause of healthcare-associated infections (HAIs). Infections caused by this bacterium, such as bloodstream infections, pneumonia, and urinary tract infections, are associated with poor patient outcomes.
The hospital environment provides numerous surfaces and devices for the bacterium to colonize and spread. Specific sources of contamination include medical equipment like mechanical ventilators, urinary catheters, and intravenous lines. The use of these invasive devices offers the organism a direct route to bypass a patient’s natural defenses and enter sterile body sites.
Transmission occurs through various routes, including direct contact between patients and hand-to-hand spread by healthcare personnel. The organism’s ability to persist on hospital surfaces, such as bedrails, door handles, and sinks, allows it to easily move between patients. The challenge is compounded by the bacterium’s ability to rapidly acquire resistance to multiple classes of antibiotics, including carbapenems, making infections difficult to treat.