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Linezolid resistance in a Staphylococcus haemolyticus strain isolated in an intensive care unit

Abstract number: 1733_388

Mazzariol A., Lo Cascio G., Koncan R., Maccacaro L., Fontana R., Cornaglia G.

Objectives: Although even recent reports confirm resistance to linezolid to be minimal among coagulase-negative staphylococci, and virtually confined to a few cases of Staphylococcus epidermidis encountered in the USA, a number of documented cases have occurred in South America and Europe, too. In a recent report from intensive care units (ICUs) in Madrid, Spain, variable resistance percentages were found in Staphylococcus epidermidis (0.81%), Staphylococcus hominis (0.71%), and most noticeably Staphylococcus haemolyticus (6.84%).

A 65-year-old male patient was admitted to the ICU of the Verona University Hospital on 1 August 2006, after extensive surgery for acute pancreatitis. Empirical therapy with teicoplanin (600 mg) was started on admission. On the 16th day of therapy, a strain of S. haemolyticus was isolated from the blood culture. The strain proved intermediate to teicoplanin (MIC, 16 mg/L), which was immediately suspended and replaced with linezolid (MIC, 0.25 mg/L). After a further 8 days, a new blood culture showed that the same strain had become resistant to linezolid (MIC, 32 mg/L).

Methods: Antimicrobial susceptibility testing was routinely performed by diffusion test according to the latest CLSI documents. The MICs to all antibiotics were determined by means of the E-test and confirmed by dilution tests. PFGE was carried out by standard procedures.

Results: MICs for recently released anti-staphylococcal compounds were as follows: daptomycin, 0.12 mg/L; quinopristin/dalfopristin, 0.5 mg/L; telavancin, 0.12 mg/L; tigecycline, 1 mg/L.

After serial passage on antibiotic-free medium, the isolate's resistance to high concentrations of linezolid was unvaried. Compared with two linezolid-susceptible S. haemolyticus strains, isolated from the same ICU in the same time period, the linezolid-resistant isolate demonstrated a significant difference in its in-vitro growth characteristics. PFGE of the two linezolid-susceptible strains would suggest a clonal relationship with the linezolid-resistant one. Further resistance characterisation and clonal analysis are ongoing.

Conclusions: After three years of linezolid use, multifocal emergence of linezolid resistance in coagulase-negative staphylococci has become an important matter of concern and involves species other than S. epidermidis. Because of the paucity of newer effective antimicrobial agents, this fact mandates stricter control over the use of this antibiotic to preserve its clinical utility.

Session Details

Date: 31/03/2007
Time: 00:00-00:00
Session name: European Society of Clinical Microbiology and Infectious Diseases
Subject:
Location: ICC, Munich, Germany
Presentation type:
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