Carbapenemase-Producing Enterobacteriaceae (CPE) are bacteria that have developed resistance to carbapenems, a class of powerful, broad-spectrum antibiotics often reserved as a last resort for severe infections. This resistance is a significant global public health concern because it severely limits the therapeutic options available to treat patients. CPE belongs to the large Enterobacteriaceae family, which includes common organisms like Escherichia coli and Klebsiella pneumoniae. When these bacteria neutralize carbapenems, they become difficult, and sometimes impossible, to treat with standard antibiotics, leading to higher mortality rates.
Understanding Carbapenemase Production
The resistance mechanism in CPE is the production of a specific enzyme called carbapenemase. Enterobacteriaceae are a natural part of the human gut flora, but they can cause serious infections, such as pneumonia, urinary tract infections, and bloodstream infections, when they spread to other parts of the body. Carbapenems are designed to treat these serious infections by targeting the bacterial cell wall.
The bacteria evade this attack by using the carbapenemase enzyme, which acts like a molecular scissor. This enzyme chemically breaks down the beta-lactam ring structure found in the carbapenem antibiotic molecule. Once the ring is broken, the antibiotic is inactivated and can no longer interfere with the bacteria’s ability to build its cell wall, allowing the bacteria to survive and multiply.
The genes that code for carbapenemase production, such as blaKPC, blaNDM, and blaOXA-48, are often located on mobile genetic elements called plasmids. These plasmids can be easily transferred from one bacterium to another, even across different species of Enterobacteriaceae, a process known as horizontal gene transfer. This high mobility allows the resistance trait to spread rapidly through a bacterial population, contributing to the organism’s designation as multidrug-resistant.
Transmission and Common Risk Factors
CPE spreads primarily in healthcare settings, where vulnerable patients are in close contact and antibiotic use is frequent. Transmission occurs through direct contact with a patient who is colonized or infected, or indirectly via contaminated environmental surfaces and medical equipment. Healthcare workers’ hands are a common vector for spreading the bacteria from one patient to another if rigorous hand hygiene protocols are not followed consistently.
Several factors increase an individual’s risk of acquiring CPE colonization or infection. Prolonged or frequent hospitalization, especially in an intensive care unit (ICU), is a major risk factor due to increased exposure. Patients residing in long-term care facilities are also at heightened risk because of communal living and frequent medical needs.
The recent or repeated use of broad-spectrum antibiotics creates selective pressure that favors the survival and growth of resistant strains. The presence of invasive medical devices, such as catheters and ventilators, provides a pathway for the bacteria to bypass the body’s natural defenses and cause an active infection. International travel and hospitalization in areas where CPE is common also introduce risk for acquisition.
Identifying CPE Through Diagnostic Testing
Detecting CPE in a clinical setting requires a combination of bacterial culture, susceptibility testing, and molecular diagnostics. Samples are collected based on the patient’s symptoms or risk factors, often including swabs from potential infection sites or the gastrointestinal tract, which is the most common site of colonization.
The initial step in the laboratory is to culture the sample to grow the bacteria. The isolate is then subjected to sensitivity testing to confirm its resistance to carbapenem antibiotics. If resistance is found, specialized phenotypic tests are performed to determine if the bacteria are producing a carbapenemase enzyme, detecting the enzyme’s activity.
Molecular tests, most commonly Polymerase Chain Reaction (PCR), are used for rapid and definitive confirmation by detecting the specific carbapenemase genes, such as blaKPC or blaNDM. This gene-based testing provides results quickly, which is valuable for making timely decisions about patient isolation and treatment. It is important to distinguish between CPE colonization, where the bacteria are present without causing illness, and CPE infection, where the bacteria are actively causing symptoms.
Treatment Options and Hospital Protocols
Treatment for an active CPE infection is highly challenging due to the limited number of effective antibiotics. Treatment plans are individualized and rely on the specific susceptibility profile of the isolated strain. Older antibiotics, such as polymyxins or tigecycline, are sometimes used, often in combination with other agents, though these drugs can be associated with higher toxicity or limited efficacy.
Newer beta-lactam/beta-lactamase inhibitor combinations have become preferred options for many CPE infections, as they are designed to bypass the resistance mechanism. Combination therapy, using two or more active antibiotics, is recommended for severe CPE infections to enhance bacterial killing and prevent the emergence of further resistance. Infectious disease specialists guide these complex therapeutic decisions.
Hospital Protocols
To prevent the spread of CPE within healthcare facilities, stringent infection control protocols are implemented immediately upon identification of a case. Patients confirmed to have CPE are placed under contact precautions, requiring a single room with dedicated toilet facilities. Healthcare personnel must consistently wear personal protective equipment (PPE), including gowns and gloves, and perform thorough hand hygiene.
Dedicated medical equipment is used for the patient, and high-level cleaning and disinfection of the patient’s environment are performed regularly to contain the organism. Surveillance programs, including the screening of high-risk patients upon admission, are employed to detect the organism early and prevent silent transmission within the facility.