ICAAC: Antibiotic Resistance Gene Goes West

CHICAGO, Sept. 21 -- A gene that allows microorganisms to resist the carbapenem antibiotics -- first seen in New York -- is spreading to the Midwest, a St. Louis researcher said here.

The so-called blaKPC gene was isolated from four patients with bacteremia at Barnes-Jewish Hospital between Aug. 1, 2006 and Jan. 31 of this year, according to Jonas Marschall, M.D., of Washington University.

That represented 1.8% of the 223 bacteremia patients he and colleagues tested in the first systematic look for the gene in the Midwest, Dr. Marschall told attendees at the Interscience Conference on Anti-microbial Agents and Chemotherapy.

The carbapenem drugs include imipenem (Primaxin) and meropenem (Merrem).

The expansion of carbapenem resistance is not only geographical, Dr. Marschall said. Of the four isolates in which the gene was found, one was lurking in an organism that has not previously been known to harbor carbapenem resistance -- Proteus mirabilis.

The gene was named Klebsiella pneumoniae carbapenemase, or KPC, after the organism in which it was first found. But that is increasingly a misnomer, Dr. Marschall said, because the gene has now been found in a wide range of Gram-negative bacteria.

Indeed, only two of the four resistant bacteria Dr. Marschall and colleagues found were K. pneumoniae. Aside from P. mirabilis, the gene was also found in a resistant strain of Enterobacter cloacae.

So researchers have added the letters 'bla' to signify the gene codes for a beta-lactamase enzyme, which confers resistance to beta-lactam antibiotics.

The researchers used polymerase chain reaction technology to find the gene, a relatively costly technique that is beyond the resources of some hospitals. But the standard microbiological technique of disk diffusion, he said, only detected three of the four, suggesting that some cases of carbapenem resistance may go undetected using standard methods.

The clinical response to detection of the blaKPC gene, he said, should be to isolate the patient immediately to prevent the gene from jumping to other strains of the resistant organism or even into other bacterial species.

But treatment is likely to be difficult, he added, since the drugs are usually reserved for the sickest patients. Indeed, of the four resistant patients in this study, there was no adequate empirical antibiotic treatment for two of the patients and one of them died, he said.

The study is evidence that it's "just a question of time" before the resistance gene is found throughout the U.S. and the rest of the world, said David Landman, M.D., of the State University of New York Downstate Medical Center in Brooklyn, N.Y., one of the researchers who first studied blaKPC.

Dr. Landman was moderator of the session -- featuring reports of blaKPC resistance from places as far afield as Israel and Brazil -- in which Dr. Marschall presented his results.

"It's just not surprising because there's so much travel," he said. But he said the rise of the resistant gene is not just a result of overuse of carbapenems, because "a majority of the patients infected with (resistant) bacteria have not received carbapenems."

The rise of resistance hasn't meant a drop in the use of the antibiotics, he noted. "But a lot of the time it's being used empirically and then you find on culture that you have a resistant organism," he said.