Gene Transfer Leads To Antibiotic Resistance In Staph Strain
Study Sheds Light on Vancomycin Resistance of Staphylococcus aureus
November 27, 2003
Rockville, MD —A dangerous new staph strain picked up its resistance to vancomycin — one of the few antibiotics effective against serious staph infections — by acquiring genes from another microbial species, scientists have found.
In a paper published in the November 28 issue of the journal Science, researchers at The Centers for Disease Control and Prevention (CDC), the University of Michigan and The Institute for Genomic Research reported that the transfer of the genes from another microbial species allowed a strain of Staphylococcus aureus to become resistant to vancomycin.
The molecular analysis is significant because S. aureus — known as staph — is a major cause of hospital- and community-acquired infections. The pathogen had developed resistance to other antibiotics but has been susceptible to vancomycin, which physicians considered to be the antibiotic of last resort for some infections. However, in June 2002, researchers found a vancomycin-resistant staph infection in a kidney-dialysis patient in Michigan.
That staph strain was found in the same wound infection with another pathogen, Enterococcus faecalis, which carried genes conferring resistance to vancomycin. To determine whether the vancomycin-resistance genes (identified in previous research) had "jumped" from one species to the other, researchers sequenced key parts of the DNA content of the microorganisms.
Their analysis confirmed earlier suspicions that the transposon that confers resistance to vancomycin — a string of genes called Tn1546 — was transferred to the staph strain from another resistant microorganism, most likely Enterococcus faecalis.
The gene transfer is accomplished through a process under which small segments of DNA called "mobile elements" jump between the DNA structures in organisms, in this case from one plasmid to another. (A plasmid is a circular strand of DNA that is located outside of the chromosome.) A previous TIGR study of a vancomycin-resistant strain of Enterococcus faecalis (published in Science in March 2003) found that an unusually high percentage of its DNA consists of mobile elements or "foreign" DNA.
Steve Gill, Ph.D., who led the TIGR work on sequencing the plasmid of the resistant S. aureus strain, says that transmission of the Tn1546 element to S. aureus "is most likely occurring more frequently than has been suggested by current studies."
The Science paper's first author is Linda M. Weigel, Ph.D., and the senior author is Fred C. Tenover, Ph.D. — both of whom are scientists at the CDC's Division of Healthcare Quality Promotion in Atlanta. Another major contributor was Don B. Clewell, Ph.D., of the University of Michigan School of Dentistry's Department of Biologic and Materials Sciences.