Israel Medical Association Journal

Objectives: To test the in vitro activity of linezolid (oxazolidinone) and other antimicrobial agents against MRSA[1] isolates recovered from hospitalized patients.

Methods: We tested 150 MRSA isolates recovered from hospitalized patients. The minimal inhibitory concentration of vancomycin, teicoplanin, pristinamycin (quinupristin-dalforistin), and linezolid was determined by the Etest method. Susceptibility to other antibiotics was tested by the disk diffusion method.

Results: All isolates were sensitive to vancomycin, teicoplanin, pristinamycin, and linezolid. The MIC₉₀ was 2.0 mg/ml for vancomycin and teicoplanin (range 0.5–2.0 mg/ml and 0.125–2.0 mg/ml, respectively), and 0.5 mg/ml for pristinamycin and linezolid (range 0.125–0.75 mg/ml and 0.125–0.5 mg/m, respectively). Of the other antibiotics, fusidic acid showed the best in vitro activity, with 96.7% susceptibility, associated with trimethoprim/sulfamethoxazole (85.8%) and minocycline (84%). Penicillin was associated with the lowest susceptibility (1.3%), associated with ofloxacin (3%) and erythromycin (14%). An increase in the minimal inhibitory concentration value of vancomycin was associated with a significant decrease in resistance to TMP-SMZ[2] (P < 0.01) and an apparent increase in resistance to other antibiotics.

Conclusion: The excellent in vitro activity of linezolid and its reported in vivo effectiveness renders it an important therapeutic alternative to vancomycin in the treatment of MRSA infection.

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[1] MRSA = methicillin-resistant Staphylococcus aureus

[2] TMP-SMX = trimethoprim/sulfamethoxazole

Background: Nasal colonization with methicillin-resistant Staphylococcus aureus in the community is being increasingly reported, but there is a general lack of data on MRSA[1] colonization in children in chronic care institutions and on colonization rates in Israeli children.

Objectives: To define the rate of MRSA nasal colonization in a generally healthy pediatric population in Jerusalem, to compare it with that of children in chronic care institutions, to define risk factors for colonization, and to compare community and hospital-acquired MRSA strains.

Methods: Anterior nares culture for the presence of methicillin-sensitive and methicillin-resistant S. aureus was taken from 831 healthy children attending primary pediatric clinics or emergency department and 118 children hospitalized in three chronic care institutions in Jerusalem.

Results: Of the 831 healthy children, 195 (23.5%) were colonized with S. aureus, as compared to 43 of 118 (36.4%) chronically institutionalized children (P < 0.005). Five of the 195 S. aureus isolates from healthy children (2.6%) were MRSA, as compared to 9 of 43 (21%) from chronically institutionalized children (P < 0.001). Older age and a family member who is a healthcare worker were associated with S. aureus colonization in the population of healthy children, and older age was associated with MRSA colonization in the chronically institutionalized children. The antibiotic susceptibility pattern was similar for both groups, and pulsed field gel electrophoresis of the isolates showed a wide and random distribution in both groups.

Conclusions: MRSA colonization in the studied pediatric community in Jerusalem was very low, whereas that of patients hospitalized in chronic care institutions was significantly higher. In the small number of isolates detected, no significant differences were found in antibiotic susceptibility or PFGE[2] pattern between hospital-acquired and community-acquired strains.