Comparison of serotyping, ribotyping and pulsed-field gel electrophoresis for distinguishing group A Streptococcus strains isolated in Albania

Conventional serotyping for T antigens, rRNA gene restriction fragment leng th polymorphism analysis (ribotyping) and pulsed-field gel electrophoresis were compared for distinguishing among group A streptococci isolated in Alb ania between 1980-1982 and in 1995. A total of twelve serotypes were identi fied among seventy GAS strains. Ribotyping revealed eight and eleven distin ct patterns after digestion with HindIII and PvuII, respectively. Twenty-th ree strains of serotype T12 were subdivided in 10 ribotypes and 11 strains of T2 serotype were differentiated in 5 ribotypes. By comparison, PFGE gene rated 37 patterns after SmaI digestion. The index of discrimination, using the Hunter-Gaston formula, was applied to assess the value of these methods for interpretation of the epidemiological data. For serotyping the value o f index was 0.85. The ribotyping system revealed an ID of 0.83 when the com bination HindIII and PvuII was used. This index reached 0.97 for PFGE. The methods used were useful to subtype the isolates of GAS.