CONTRIBUTION OF A TYPING METHOD BASED ON IS256 PROBING OF SMAI-DIGESTED CELLULAR DNA TO DISCRIMINATION OF EUROPEAN PHAGE TYPE-77 METHICILLIN-RESISTANT STAPHYLOCOCCUS-AUREUS STRAINS

The incidence of infections with phage type 77 methicillin-resistant S taphylococcus aureus (MRSA) strains increased in France in 1987. These strains are widespread in numerous European hospitals. The SmaI restr iction profiles of total DNA extracted from 74 phage type 77 MRSA stra ins isolated from 1987 to 1994 in 10 hospitals in eight European citie s (in France, Belgium, and Spain) were analyzed. Hybridization with a probe containing a 468-bp DNA fragment from within the transposase gen e of the insertion sequence IS256 was also examined. Forty-three SmaI profiles were detected, Twenty major genotypes were identified, and ea ch genotype contained strains with the same profile or profiles which differed by no more than three bands, Strains isolated in different co untries and at several-year intervals were often grouped within the sa me genotype, A larger number of genotypes could be discriminated by an alysis of the patterns of hybridization with the IS256 probe, SmaI res triction fragments with the same apparent electrophoretic mobility cou ld, in some cases, be distinguished by the presence or the absence of nucleotide sequences hybridizing,vith IS256. The strains that grouped within the same genotype after hybridization with IS256 were mostly th ose isolated in the same hospital and at less than 12-month intervals. Consequently, the IS256 probe that we used improved restriction profi le analysis for discrimination between the intrahospital, outbreak-rel ated phage type 77 MRSA strains and the endemic strains disseminated i n various cities and countries.