[Occurrence of methicillin-resistant strains in Poland and their characteristics]

The investigation was performed on 923 strains of S. aureus isolated from clinical material obtained from several regions of Poland. Resistance to methicillin was tested by a dilution method on a solid Mueller-Hinton medium supplemented with 2% of NaCl. Strains exhibiting MIC higher than 4 micrograms/ml were determined as resistant. Resistance to other antibiotics (P, Am, CB, CF, CH, MA, Ge, Bs, E, L, Dx) was tested by a disc method. Bacteriophage typing of S. aureus was performed by a method described by Blair and Williams in RTD and RTD x 100, using basic set of phages and additional phages (88, 89, 187). MRSA were present in various regions of the country with similar frequency (from 3.3% to 8.3%). In one center only the percentage was as high as 52.3%. High percentage of MRSA was noted in burned patients (59.9) and these strains were obtained at one center. Within the MRSA III phage group was dominating as well as non-typable strains and inhibited at 100 x RTD-35.4%. MRSA most frequently were typing with phages 88-40.9%, 89-35.0%, 85-24.0%, and they rarely belonged to the phage group II. Among MRSA strains higher percentage of antibiotic-resistance was noted, as compared with other strains. About 60% of MRSA strains were resistant to 6-8 antibiotics. The dominating resistance concerned penicillins, cephalosporins, aminoglycosides, tetracyclines and erythromycin.