Carbapenem-Resistant Enterobacteriaceae (CRE) is a type of bacterium that has developed resistance to a class of powerful antibiotics. These organisms are often referred to as “superbugs” because they can defeat many of the drugs healthcare professionals rely on to fight infection. Understanding how these bacteria function and spread is an important step in controlling their impact on global health.
Defining Carbapenem-Resistant Enterobacteriaceae
CRE stands for Carbapenem-Resistant Enterobacteriaceae, a group of bacteria that includes common germs like Klebsiella pneumoniae and Escherichia coli (E. coli). This family of Gram-negative bacteria is normally found in the human gut, where they are typically harmless. However, when these bacteria spread outside the intestinal tract, they can cause infections such as urinary tract infections or pneumonia.
The “carbapenem-resistant” designation means these bacteria are immune to carbapenems, which are a class of broad-spectrum antibiotics often reserved as a last-resort treatment for severe, multidrug-resistant infections. The most concerning mechanism of resistance involves the bacteria acquiring the genetic instructions to produce carbapenemase enzymes. These enzymes, such as Klebsiella pneumoniae carbapenemase (KPC), chemically dismantle the carbapenem antibiotic molecule, rendering it useless before it can attack the bacterial cell wall.
The genes that code for these carbapenemase enzymes are often located on mobile genetic elements, called plasmids, which allows the resistance to be easily transferred between different species of bacteria. Other resistance mechanisms involve decreasing the number of porin channels, which are tiny openings in the bacterial cell wall that antibiotics use to enter the cell. The bacteria may also increase the activity of efflux pumps, which actively flush the antibiotic drug out of the cell before it can reach its target.
Transmission Pathways and High-Risk Settings
CRE primarily spreads through direct or indirect contact with colonized or infected individuals, particularly within healthcare environments. The bacteria can colonize a person’s gastrointestinal tract or skin without causing an active infection, allowing even colonized patients to spread the organism. Transmission often occurs via the contaminated hands of healthcare personnel who have touched a patient, a wound, or bodily fluids like stool.
Contaminated environmental surfaces and medical equipment, known as fomites, also serve as significant reservoirs for CRE transmission. Sinks, toilets, and shared medical devices can harbor the bacteria, especially when cleaning protocols are not strictly enforced. Healthcare settings, including acute care hospitals, long-term care facilities, and intensive care units, are the most common environments for CRE transmission and outbreaks.
Several patient risk factors significantly increase the likelihood of acquiring a CRE infection. Patients who require invasive medical devices, such as mechanical ventilators, urinary catheters, or central venous lines, are at higher risk as these devices provide a pathway for bacteria to enter the body. Prolonged or repeated courses of antibiotics can disrupt the normal balance of gut bacteria, allowing resistant CRE to thrive and colonize the patient. Patients with weakened immune systems, poor functional status, and extended hospital stays are also more susceptible to colonization and subsequent infection.
Clinical Manifestations and Treatment Strategies
CRE can cause several types of severe infections, with the specific symptoms depending on the location in the body where the bacteria are growing. The most common manifestations include urinary tract infections, which may present with pain during urination or fever. However, CRE is also a known cause of pneumonia, bloodstream infections, and intra-abdominal abscesses. Infections of the bloodstream and lungs are associated with the highest mortality rates.
Diagnosis requires laboratory testing to confirm the presence of the bacteria and its specific resistance profile. Treatment often relies on a small group of “last-resort” antibiotics, including polymyxins (like colistin), tigecycline, or aminoglycosides.
Newer combination therapies pair a carbapenem with an inhibitor drug designed to neutralize the carbapenemase enzyme. Agents such as ceftazidime-avibactam or meropenem-vaborbactam offer more effective options against certain types of CRE. Beyond antibiotics, rigorous infection control measures are paramount to prevent spread within healthcare facilities, including placing patients on contact precautions, enforcing meticulous hand hygiene, and ensuring thorough cleaning and disinfection of the environment and equipment.