MAR 26, 2015 7:37 AM PDT

Common Bacteria Poised to Morph Into Superbugs?

WRITTEN BY: Judy O'Rourke
Antibiotic resistance is on its way to spreading around the world among bacteria that are often involved in respiratory and urinary infections in hospitals, according to researchers.

Researchers from Washington University School of Medicine in St Louis have released a study showing that two genes that bestow resistance against an exceptionally powerful class of antibiotics can be readily spread among a family of bacteria responsible for a considerable number of hospital-associated infections.
Bacteria that cause many hospital-associated infections are ready to quickly share genes that allow them to resist powerful antibiotics. The illustration, based on electron micrographs and created by the CDC, shows one of these antibiotic-resistant bacteria.
It was widely reported not long ago that drug-resistant germs in the same family of bacteria infected several patients at two hospitals in Los Angeles. Medical scopes-thought to have been contaminated with bacteria that can resist carbapenems-were implicated as the culprits for the infections. Carbapenems are broad spectrum antibiotics that are meant to be used only for acutely sick patients or those infected by resistant bacteria.

"Carbapenems are one of our last resorts for treating bacterial infections, what we use when nothing else works," says senior author Gautam Dantas, PhD, associate professor of pathology and immunology. "Given what we know now, I don't think it's overstating the case to say that for certain types of infections, we may be looking at the start of the post-antibiotic era, a time when most of the antibiotics we rely on to treat bacterial infections are no longer effective."

Dantas calls for rigorously limiting use of carbapenems to cases where it would be the only viable treatment (ie, where no other treatments are available to help the patient).

The researchers studied the family of bacteria known as Enterobacteriaceae (of which E. coli, Klebsiella pneumonia, and Enterobacter are members). Some strains of the bacteria are benign-not only don't they make people sick, but they can be guardians of good health. For people with compromised immune systems, though, becoming infected with carbapenem-resistant versions of these bacteria can be fatal.

The researchers note that the Centers for Disease Control and Prevention have ranked carbapenem-resistant Enterobacteriaceae among the top three most urgent threats among emerging forms of antibiotic-resistant disease. For patients whose immune systems are compromised, the fatality rate for these infections is more than 50 percent, according to studies.

KPC is one of two genes that are chiefly responsible for carbapenem-resistant versions of these disease-causing bacteria. This gene occurred in the bacteria that contaminated medical equipment at UCLA's Ronald Reagan Medical Center, Los Angeles, where several patients fell ill and two patients died. This gene was also detected in New York in 2001, and it rapidly traveled around most of the world-bypassing India, Pakistan, and other South Asian countries.

NDM-1, another carbapenem resistance gene, was identified in 2006 in New Delhi, India, and soon after discovered throughout South Asia. The majority of patients infected by bacteria with NDM-1 have had an epidemiological connection with South Asian countries.

The geographically exclusive nature of these two resistance genes interested the researchers, who compared the genomes of carbapenem-resistant bacteria isolated in the United States with those of carbapenem-resistant bacteria isolated in Pakistan for the study.

The researchers found that the bacteria's high genetic similarity suggests that the antibiotic resistance genes could be shared freely between bacteria from the two geographic regions.

The researchers also sequenced a part of bacterial genetic material called plasmids, identifying some important cases in which the plasmids carrying NDM-1 or KPC were nearly the same. So, they could easily promote the transmission of antibiotic resistance between disease-causing bacteria found in the United States and South Asia. (Such commingling may already be under way in parts of China.)

"Our findings also suggest it's going to get easier for strains of these bacteria that are not yet resistant to pick up a gene that lets them survive carbapenem treatment," Dantas says. "Typically, that's not going to be a problem for most of us, but as drug-resistant forms of Enterobacteriaceae become more widespread, the odds will increase that we'll pass one of these superbugs on to a friend with a weakened immune system who can really be hurt by them."

The research, "KPC and NDM-1 are harbored by related Enterobacteriaceae strains and plasmid backbones form distinct geographies," is available online ahead of print in Emerging Infectious Diseases, June 2015.

[Source: Washington University School of Medicine in St Louis]
About the Author
  • Judy O'Rourke worked as a newspaper reporter before becoming chief editor of Clinical Lab Products magazine. As a freelance writer today, she is interested in finding the story behind the latest developments in medicine and science, and in learning what lies ahead.
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