Infection Control

New concerns arise with antibiotic-resistant organisms

Briefings on Infection Control, March 1, 2010

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Over the past several years, MDROs have become a leading concern for IPs attempting to reduce their hospital's healthcare-associated infection (HAI) rate.

Although MRSA is the most common drug-resistant organism, other bacteria, including VRE and certain Gram-negative bacilli, have also evolved to become less susceptible to drug treatments. Additionally, diseases such as TB are becoming resistant to drugs, leading to potentially dire situations. In December 2009, the first U.S. case of extremely drug-resistant TB was discovered in Florida. The World Health Organization (WHO) says that about 5% of TB cases are resistant to the two primary drugs traditionally used to treat TB: rifampin and isoniazid. Worldwide, there are about 40,000 new cases of extensively drug-resistant TB, according to the WHO.

A new study published in the February Infection Control and Hospital Epidemiology indicates that drug-resistant strains of Acinetobacter have increased more than 300% from 1999 to 2006. The study was conducted by Extending the Cure, a research project under Resources for the Future that studies the growing problem of antibiotic resistance. The findings suggest that this new bacteria is becoming resistant to nearly every drug, leaving doctors with fewer treatment options, says Michael R. Eber, BSE, researcher for the Center for Disease Dynamics, Economics and Policy at Resources for the Future in Washington, DC, who was involved with the study.

"Acinetobacter is particularly troubling because it's resistant to a lot of different drugs used to treat it," Eber says. "Even some of what are considered last-line treatments are sometimes resistant."

(For additional information on this study, see the sidebar on p. 3.)

A separate study published in the January Microbiology found that certain organisms can actually become less susceptible to both disinfectants and antibiotics. Researchers grew the bacteria Pseudomonas aeruginosa in the presence of a common disinfectant—benzalkonium chloride—and found that the bacteria eventually became 12 times less susceptible to the disinfectant and, perhaps more importantly, 256 times more resistant to the drug ciprofloxacin.

Obviously, this poses several problems in terms of basic infection prevention, says Gerard T.A. Fleming, researcher for the Department of Microbiology at the School of Natural Sciences at the National University of Ireland in Galway and lead researcher for the study.

"We know we have a problem from a laboratory point of view in the sense that we often view disinfectants as the first line of defense, so in a hostile environment you use disinfectants to reduce the number of bad germs," Fleming says. "You're never going to kill them in total; you're going to reduce the numbers.

"If a person becomes infected and develops the disease, we then use the antibiotic to control that disease," he says. "So I often look at the disinfectant as being the first line of defense and the antibiotics being the second line of defense, and the worry here now is that from this study we have shown that you can actually cross that barrier between the first and second line of defense."

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