September 1, 2015
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NDM-1 (New Delhi metallo-beta-lactamase)

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NDM-1 facts

  • NDM-1 has been reported most commonly from India and Pakistan but is spreading throughout the world as people travel from country to country.
  • The first three cases of NDM-1 in the United States were reported in June 2010.
  • Bacteria that express NDM-1 usually have other resistance factors. Most strains are resistant to all commonly used antibiotics.
  • Routine antibiotic-sensitivity testing can detect resistance to beta-lactam antibiotics. Specific testing for NDM-1 is not routinely available. Fortunately, it is not necessary to determine if carbapenem resistance is specifically due to NDM-1 because treatment is guided by the antibiotic-sensitivity testing.
  • Most NDM-1 strains remain sensitive to an older, little-used antibiotic called colistin. Some strains have also been sensitive to tigecycline or aztreonam.
  • NDM-1 is carried by bacteria that commonly inhabit the bowel. Strains spread from person to person through contact with contaminated hands or items.
  • Good hand hygiene practices will reduce the risk of spreading or acquiring NDM-1. In hospitals, hand hygiene is critical and patients with NDM-1 should be placed in private rooms and health-care workers should used gowns and gloves when entering the room.
  • To reduce the risk that NDM-1 will arise, physicians and hospitals should ensure that antibiotics are used judiciously and appropriately.

What is NDM-1?

NDM-1 stands for New Delhi metallo-beta-lactamase, which is an enzyme produced by certain strains of bacteria that have recently acquired the genetic ability to make this compound. The enzyme is active against other compounds that contain a chemical structure known as a beta-lactam ring. Unfortunately, many antibiotics contain this ring, including the penicillins, cephalosporins, and the carbapenems.

There are many types of beta-lactamases. Most are only active against older beta-lactam antibiotics but are not active against newer agents like the carbapenems. However, bacteria that produce NDM-1 are resistant to all commonly used beta-lactam antibiotics, including carbapenems. Some antibiotics like aminoglycosides and fluoroquinolones do not contain beta-lactam rings. Unfortunately, the bacteria that have acquired NDM-1 have also acquired other resistance factors and most are already resistant to aminoglycosides and fluoroquinolones. The addition of NDM-1 production has the ability to turn these bacteria into true superbugs (bacteria resistant to usually two or more antibiotics) which are resistant to virtually all commonly used antibiotics.

NDM-1 infection was first identified (in 2009) in people who resided in or traveled to the India and Pakistan. Antibiotic use in India is not as restricted as it is in the United States and some researchers feel overuse of carbapenems allowed NDM-1 to develop. Others point to the advent of medical tourism as a cause of NDM-1 spread among countries. Medical tourism refers to patients who travel to a country to get medical care that is not available or is more expensive in their own country. The three first cases of NDM-1 infection in the United States were identified in June 2010 in Americans who had recently sought medical care in India. Vacation and business travel have also played a role in introducing NDM-1 bacteria into countries outside of the Indian subcontinent. Cases have now been detected in many countries, including Great Britain, Canada, Sweden, Australia, Japan, and the United States.

NDM-1 is a newly identified problem, only recognized since about December 2009 in the medical literature. To date, there have fewer than 100 cases identified outside of the Indian subcontinent, so this is not a pandemic like bird flu or swine flu. However, the number of cases is growing and the concern is that these highly resistant bacteria (bacteria carrying this NDM-1) could supplant more antibiotic-sensitive strains. If this happens, the antibiotic arsenal that has been built up over the last 80 years will be seriously compromised.

Medically Reviewed by a Doctor on 6/30/2015


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