Systemic and intracerebral infections of mice with Listeria monocytogenes successfully treated with linezolid

Linezolid is an oxazolidinone derivative which is active mostly against Gra mpositive bacteria, In this work its activity against the facultatively int racellular bacterium Listeria monocytogenes was examined in vitro, in tissu e culture and in animal models of systemic and intracerebral infection and compared with ampicillin which is the antibiotic of choice for treatment of listeriosis. All strains of L, monocytogenes were susceptible to the subst ance, with minimal inhibitory concentrations (MICs) determined by E-test ra nging from 0.38 to 1.5 mg/l which is below the preliminary breakpoint of th is substance. Linezolid was bacteriostatic against L, monocytogenes since u p to 64 times the MIC did not kill the bacteria in 24 hours. Linezolid was also bacteriostatic on L, monocytogenes in infected tissue culture cells. I n animal models of systemic and intracerebral infection, linezolid was able to inhibit bacterial growth but was clearly less effective than ampicillin , In conclusion, linezolid might be useful for the treatment of infections with L. monocytogenes in humans when ampicillin may not be used.