[A system of step-by-step differentiation of methicillin-resistant Staphylococcus aureus]

One hundred and eighty four strains of methicillin resistant Staphylococcus aureus (MRSA) isolated in pyosurgical and burn departments of Moscow, Minsk, Omsk, Tbilisi, Vologda, Smolensk and Dushanbe were differentiated with using phages of the International Set (BIS), two collections of experimental phages and two-probe fingerprinting. More than 50 per cent of the isolates could not be typed by the BIS phages. The Experimental Collection of the N.F. Gamaleya Research Institute of Epidemiology and Microbiology (Moscow) was more useful in the differentiation in comparison to the Experimental Collection of the London Health Centre. A new approach applied by us to the establishment of our collection i.e. screening of cultures with a definite specificity of the system of the restriction-modification (by a modified phage 85) followed by their differentiation with respect to the specificity of the prophages (by the induced phages with the respective modification specificity) provided reliable and reproducible results. Our collection made it possible to classify the phage type 85 strains which as was confirmed by the fingerprinting data belonged to 3 different genotype variants. The fingerprinting had no advantages over the typing by the phages of the more extended phage set and was recommended for differentiation of the strains (14 per cent) not sensitive to the phages used. A step-by-step scheme for typing MRSA easy for use in clinical and epidemiological laboratories is described.