Published Date: 2001-07-30 23:50:00
Subject: PRO/EDR> Staphylococcus, MRSA, linezolid resistant - USA
Archive Number: 20010730.1493
STAPHYLOCOCCUS, MRSA, LINEZOLID RESISTANT - USA
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MRSA, imported - Canada ex UK 20010517.0960Date: 25 Jul 2001
From: Deane L Burns <deane@multiboard.com>
Source: Eurosurveillance Weekly [edited
<http://www.eurosurv.org/>
Linezolid-resistant MRSA isolated from a patient in the United States
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A strain of methicillin-resistant _Staphylococcus aureus_ (MRSA) that
was resistant to the new antibiotic linezolid was isolated from an
85-year-old patient undergoing peritoneal dialysis in the United
States, according to a report published in the Lancet last week (1).
MRSA infections are a major problem in many hospitals, and treatment
with other antibiotics may be indicated, usually vancomycin. Linezolid
is a new antibiotic that may be an alternative to vancomycin (2). It
prevents the formation of functional ribosomal complexes, thus
inhibiting protein synthesis, and it is active against MRSA, _S.
epidermidis_, streptococci (including penicillin-resistant strains of
_S. pneumoniae_), and enterococci (including vancomycin-resistant
strains of _Enterococcus faecalis_ and _E. faecium_). It is
bacteriostatic against most susceptible bacteria.
Over a 3-week period, 11 linezolid-susceptible isolates were recovered
from the patient's peritoneal dialysis fluid, during which time the
patient (who was intolerant of vancomycin) received treatment with
linezolid. The isolates had identical susceptibility profiles and were
indistinguishable by pulsed field gel electrophoresis (PFGE). Of the
subsequent isolates, 3 were resistant to linezolid and differed from
earlier isolates in their other antimicrobial susceptibilities.
Minimum inhibitory concentrations of linezolid were 2 mg/L for
linezolid-susceptible and >32 mg/L for linezolid-resistant isolates.
By PFGE, the linezolid-resistant isolates were unrelated to the
earlier susceptible isolates. Of the resistant isolates, 2 were
indistinguishable from each other, and a third differed by just one
band. Linezolid treatment was discontinued when the resistant isolate
was identified, and during the remainder of his hospital stay, the
patient received ampicillin, azithromycin, gentamicin, levofloxacin,
and quinupristin-dalfopristin for the MRSA and for _E. faecalis_,
which was grown from blood cultures, and _Pseudomonas aeruginosa_,
which was also isolated from peritoneal fluid. All cultures were
negative within one week, but 3 weeks after the last positive
cultures, the patient died of his underlying disease.
Possible explanations for this unexpected finding include the
acquisition of an unrelated linezolid-resistant MRSA isolate from an
external source; the appearance of a previously undetected
linezolid-resistant clone within the patient; or the emergence of
resistance to linezolid in a previously undetected susceptible clone
that was coinfecting the patient. No linezolid-resistant _S. aureus_
was recovered from any other patient at the institution, suggesting
that the third of these possibilities is the most plausible. The
emergence of resistance to linezolid in MRSA is an unwelcome
development, and future cases will have to be watched closely. Strict
infection control measures are essential as and when such strains are
encountered in the future.
References:
1. Tsiodras S, Gold HS, Sakoulas G, Eliopoulos GM, Wennersten C,
Venkataraman L, et al. Linezolid resistance in a clinical isolate of
_Staphylococcus aureus_. Lancet 2001; 358: 207-8.
<http://www.thelancet.com/journal/vol358/iss9277/full/llan.358.9277.or
iginal_research.16979.1>
2. Linezolid for Gram positive infections. Drug Ther Bull 2001; 39(7):
54-6. <http://www.which.net/health/dtb/main.html>
--
Deane Burns
Deane L. Burns Consulting
London, Ontario, Canada
<deane@multiboard.com>
[The authors have detected a mutation in the 23S ribosome subunit that
could explain the linezolid resistance observed. - Mod.ES
................................es/pg/jw
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