A fast-track research letter published in this week's issue of THE LANCET describes the case of a patient whose infecting bacterium developed resistance to one of the new so-called bug-busting antibiotics.
Multidrug resistant bacteria have caused enormous difficulties worldwide over the past few decades. Scientists had hoped, however, that new drugs currently available for prescription would help to suppress the emergence of superbugs such as meticillin-resistant Staphylococcus aureus (MRSA) that created media headlines last year.
The new antibiotic linezolid has been approved for the treatment of infections caused by various gram-positive bacteria, including MRSA and vancomycin-resistant enterococci (VRE). Although instances of linezolid resistance in VRE have been previously reported (Lancet 2001; 357: 1179), resistance has not been encountered among clinical isolates of S. aureus. Mary Jane Ferraro from Massachusetts General Hospital, Boston, USA, identified an MRSA isolate resistant to linezolid that was recovered from an 85-year-old patient treated for dialysis-associated peritonitis. Co-investigators at Beth Israel Deaconess Medical Center, Boston, USA, have characterised the isolate and determined its mechanism of resistance to linezolid.
Mary Jane Ferraro comments: "This is an important finding because up to now the only other isolate of Staphylococcus aureus that was resistant to linezolid was produced in the laboratory. Unlike previous clinical isolates of linezolid-resistant enterococci, this high-level resistance has occurred in S aureus, which is much more virulent. Clinicians should not assume that all S aureus isolates are susceptible to linezolid, but it highlights the need for clinical laboratories to perform susceptibility tests on new antibiotics being used for patients in their hospital."
Howard Gold, a member of the team at Beth Israel Deaconess that characterised the isolate, adds: "The finding of this resistant isolate must be put in perspective. So far this appears to be a very rare event, but the drug has only been widely used in the USA during the past year. There is no evidence of further spread or other occurrences of this organism. The finding of occasional resistance should not diminish the importance of new antibiotics like linezolid that are active against multiresistant bacteria like MRSA."
Contact: Dr Howard Gold, Division of Infectious Diseases, Beth Israel Deaconess Medical Center, Boston, MA USA, T) +1 617 632 0760; F) +1 617 975 5235, E) firstname.lastname@example.org
Dr Mary Jane Ferraro, Clinical Microbiology Laboratories, Massachusetts General Hospital, Gray B-526, Boston, MA 02114, USA; T) +1 617 726 3612; F) +1 617 726 5957; E) email@example.com