What Is NDM Bacteria and Why Is It a Threat?

Bacteria carrying the New Delhi metallo-beta-lactamase (NDM) gene present a challenge to modern medicine. This gene produces an enzyme that confers resistance to many antibiotics, including carbapenems, which are often a last line of defense. Bacteria with the NDM gene are called “superbugs” because the infections they cause are difficult to treat, rendering many standard therapies ineffective.

The NDM Enzyme and Carbapenem Resistance

The NDM enzyme is part of a family called metallo-beta-lactamases. Its primary mechanism is to break down beta-lactam antibiotics, a category that includes penicillins, cephalosporins, and carbapenems. The enzyme works by breaking a key bond in the antibiotic’s molecular structure, inactivating it before it can kill the bacterium.

Carbapenems were developed to overcome resistance from other beta-lactamase enzymes, but the NDM-1 enzyme can neutralize nearly all drugs in this class. By inactivating these last-resort antibiotics, the NDM enzyme leaves clinicians with few, and often more toxic, treatment alternatives. This resistance mechanism is a primary reason why infections with NDM-positive bacteria are linked to higher rates of treatment failure.

The gene that codes for the NDM enzyme, blaNDM-1, provides a survival advantage to the bacteria. When a patient is treated with carbapenems, susceptible bacteria are killed, but NDM-producing bacteria can thrive without competition. This selective pressure allows the resistant strain to proliferate and establish a severe infection.

Bacterial Hosts of the NDM Gene

The blaNDM-1 gene is not confined to a single type of bacterium; it has been identified in several Gram-negative species that cause infections in healthcare settings. These opportunistic pathogens are responsible for many hospital-acquired infections. The most frequent carriers include:

• Klebsiella pneumoniae
• Escherichia coli
• Acinetobacter baumannii
• Pseudomonas aeruginosa

A defining feature of NDM-mediated resistance is its mobility. The gene is located on plasmids, which are small, circular pieces of DNA that exist independently of the bacterial chromosome. These plasmids can be easily transferred from one bacterium to another, even between different species, through a process called horizontal gene transfer.

This mobility accelerates the spread of resistance, allowing a diverse range of bacteria to become resistant. The presence of the blaNDM-1 gene on these mobile elements is a primary reason for its swift dissemination among pathogens across the globe.

Global Spread and Transmission Pathways

The NDM resistance mechanism was first identified in 2008 in a patient in Sweden who had received medical care in New Delhi, India. This pointed to the Indian subcontinent as where the gene likely emerged. Since then, the gene has been detected in pathogens in more than 70 countries. International travel is a key factor in this global spread, as individuals acquire the bacteria abroad and carry them to their home countries.

Transmission occurs mainly within healthcare facilities. Patients who are colonized—carrying the bacteria without signs of infection—can serve as reservoirs. The bacteria spread on the hands of healthcare workers or through contact with contaminated surfaces and medical equipment. This makes hospitals and long-term care facilities common sites for outbreaks.

Community-acquired transmission is also a concern. NDM genes in environmental samples, like public water sources in areas with high prevalence, suggest these reservoirs contribute to the spread outside of hospitals. The combination of medical tourism, travel, and healthcare-associated transmission makes containing NDM a global public health challenge.

Clinical Impact and Vulnerable Groups

Bacteria carrying the NDM gene can cause a wide range of infections, including:

• Urinary tract infections (UTIs)
• Bloodstream infections (bacteremia)
• Pneumonia
• Surgical wound infections

Because these organisms are resistant to most standard antibiotics, the resulting illnesses are linked to higher rates of morbidity and mortality. Patients with these infections often require longer hospital stays and more intensive care, which elevates healthcare costs.

Certain patient populations are particularly vulnerable to acquiring these infections. High-risk groups include:

• Individuals hospitalized for prolonged periods, especially in intensive care units (ICUs)
• People with weakened immune systems
• Those with indwelling medical devices like catheters and breathing tubes
• Patients who have recently undergone surgery
• Individuals with prior exposure to broad-spectrum antibiotics

A history of travel to or hospitalization in regions where NDM is endemic, such as the Indian subcontinent, is a strong risk factor. Patients may become colonized with the bacteria during their travels and later develop an infection, sometimes months after returning home. The combination of extensive antibiotic resistance and the ability to cause life-threatening conditions makes NDM-producing bacteria a clinical threat to medically fragile patients.

Addressing NDM Infections: Treatment and Prevention

Treating infections from NDM-producing bacteria is challenging due to extensive drug resistance. With carbapenems ineffective, clinicians turn to a limited number of alternatives like colistin and tigecycline. These last-resort drugs can have significant side effects, like kidney toxicity, and resistance to them is also emerging. Treatment decisions must be guided by laboratory testing to determine the organism’s susceptibility profile.

Given the limited treatment options, preventing the spread of NDM-producing organisms is a priority. In healthcare settings, this requires infection control measures, including:

• Practicing good hand hygiene
• Using contact precautions for infected or colonized patients
• Cleaning and disinfecting patient rooms and medical equipment
• Screening high-risk patients for colonization upon hospital admission

Antibiotic stewardship programs are another component of the response. These programs promote the appropriate use of antibiotics to reduce the selective pressure that drives resistance. Public health surveillance is also necessary to track the geographic spread of NDM and detect outbreaks early. Combating NDM requires infection control, antibiotic management, and continued research.