The Real and Evolving Threat of Superbugs: A Primer
Just how super is the latest superbug? The good news is that the infected U.S. patient has recovered. The bad news: mcr-1, the resistance gene identified in this strain of E. coli, has brought us another frightening step closer to a “post-antibiotic” era.
In recent years, antimicrobial resistance among Gram-negative bacteria (E. coli, Klebsiella, Pseudomonas, Acinetobacter, Salmonella, and others) has been a growing public health concern. Most of the increase in resistance has been the result of mobile genetic elements that can easily transfer resistance from one bacterium to another, allowing bacteria to “catch” antibiotic resistance from one another.
To make matters worse, resistance enzymes are often packaged together. One genetic “cassette” can carry multiple resistance determinants, thereby spreading resistance to more than one class of antibiotics at the same time.
Early on, we relied on the carbapenem class of antibiotics to treat infections caused by multidrug-resistant (MDR) organisms such as the “ESBLs” (extended-spectrum beta-lactamase-producing organisms). But carbapenemase-producing organisms soon developed, and resistance to carbapenems spread quickly.
In 2009, the emergence of a “super” kind of carbapenem resistance gene, ndm-1 (New Delhi metallo-beta-lactamase) was found to be highly resistant to many antibiotic classes, including:
- the carbapenems and other beta-lactams (penicillin derivatives and cephalosporins)
- the fluoroquinolones (ciprofloxacin, levofloxacin, et al)
- the aminoglycosides (gentamicin, amikacin, et al).
These antibiotic classes include the main […]