NEW YORK (Reuters Health) - In the United States alone, there have been 11 reported cases of Staphylococcus aureus infection that were either partly or fully resistant to vancomycin, according to a new report. So far, resistant isolates have been susceptible to trimethoprim-sulfamethoxazole.
In the August 15th issue of Clinical Infectious Diseases, researchers from the Johns Hopkins University School of Medicine in Baltimore, Maryland, review infection control and management issues related to S. aureus organisms with reduced susceptibility to vancomycin.
According to the article, written by Dr. Sara E. Cosgrove and colleagues, resistance is defined as a minimum inhibitory concentration of vancomycin of at least 32 µg/ml. Isolates for which the minimum inhibitory concentration of vancomycin is between 8 and 16 are classified as “intermediate.”
“The proposed mechanisms of resistance...are distinctly different” for the intermediate and fully resistant organisms, the authors note.
Among the intermediate organisms, a thickened cell wall with several extra peptidoglycan layers is the primary factor responsible for the reduced drug susceptibility. In contrast, in the two reported cases with full resistance to vancomycin, the clinical isolates contained the vanA gene, which is known to mediate vancomycin resistance in enterococci.
“All microbiology laboratories should have procedures in place for selection of S. aureus strains that should be screened for decreased susceptibility to vancomycin,” the authors urge.
They add that susceptibility should be determined with a quantitative method. But, they warn, the intermediate isolates “are slow growing” and may not appear on the primary culture plate for 2 days or more. Furthermore, the colonies may have “variable -- even atypical -- morphologies.”
There is no standard treatment approach to infections with these organisms. “Of utmost importance,” the authors say, is removal of infected indwelling devices and debridement of infected sites.
Vancomycin monotherapy is usually ineffective, but in the United States, all of the intermediate-resistance isolates thus far have been susceptible to trimethoprim-sulfamethoxazole and tetracycline. The two fully resistant isolates were susceptible to trimethoprim-sulfamethoxazole but not to tetracycline. Linezolid has also been used in combination regimens.
Since nasal colonization is likely, “We recommend that the anterior nares of patients be cultured once the infection is cleared,” the researchers write. “If the patient is colonized, decolonization should be attempted with mupirocin applied to the nares.” Chlorhexidine washes can also be considered.
“Given the rapid spread of methicillin-resistant S. aureus and vancomycin-resistant enterococci within hospitals shortly after their emergence as pathogens, the specter of a similar pattern of spread with (S. aureus partly and fully resistant to vancomycin) has elicited great concern in the infection-control and public health arenas,” Dr. Cosgrove and colleagues write.
They warn: “It is prudent to assume that spread from patient to patient can occur...on the hands of health care workers, on contaminated equipment, and from nasal shedding.”
Source: Clin Infect Dis 2004;39:539-545. [ Google search on this article ]
MeSH Headings:Biological Phenomena: Biological Phenomena, Cell Phenomena, and Immunity: Biological Sciences: Biology: Drug Resistance, Microbial: Genetics: Genetics, Microbial: Microbiologic Phenomena: Pharmacogenetics: Biological SciencesCopyright © 2002 Reuters Limited. All rights reserved. Republication or redistribution of Reuters content, including by framing or similar means, is expressly prohibited without the prior written consent of Reuters. Reuters shall not be liable for any errors or delays in the content, or for any actions taken in reliance thereon. Reuters and the Reuters sphere logo are registered trademarks and trademarks of the Reuters group of companies around the world.
