In vitro susceptibility of Gram-positive pathogens to linezolid and teicoplanin and effect on outcome in critically ill patients

Objectives: To determine the prevalence of teicoplanin and linezolid resistance amongst Gram-positive pathogens isolated in the intensive care unit (ICU) and the impact of any resistance on clinical outcome. Methods: Gram-positive isolates were collected from two critical care units over 1 year. All patients were screened weekly for methicillin-resistant Staphylococcus aureus(MRSA). Susceptibility to teicoplanin and linezolid was tested by Etest. The length of hospital and critical care unit stay and the use of antibiotics in each patient were recorded. Results: Reduced susceptibility to teicoplanin (MIC >= 16 mg/L) was found in 21 [3.3% (95% CI 2.0-5.0%) 6 patients] of 643 strains of MRSA versus none of 374 methicillin-susceptible S. aureus (MSSA) [< 0.3% (95% CI 0-0.9%)]. Of 49 enterococci 3 were teicoplanin-resistant. All Gram-positive isolates were susceptible to linezolid. The length of treatment with teicoplanin and outcome of patients infected with these strains were similar to that of susceptible strains. MRSA was a more common cause of infection than MSSA but a less frequent colonizer. Conclusions: Resistance to teicoplanin remains at a comparatively low level and there was no clear relationship between susceptibility and outcome in this critically ill population. There was no resistance in Gram-positives to linezolid but this should be kept as a reserve antibiotic to maintain its activity.