Molecular epidemiology of penicillin-susceptible, multidrug-resistant serotype 6B pneumococci isolated from children in Greece

Since January 1996, and over a 3-year time span, a significant spread of se rotype 6B multidrug-resistant (MDR) pneumococci, susceptible to penicillin and resistant to erythromycin, clindamycin, tetracycline, chloramphenicol, and trimethoprim-sulfamethoxazole, was noted in young carriers living in ce ntral and southern Greece. Using restriction fragment end labeling and peni cillin binding protein (PBP) genotyping, we studied 41 serotype 6B penicill in-susceptible MDR pneumococci isolated during two independent studies in G reece. Forty (98%) of these 41 isolates were strongly related, representing a single lineage (genetic relatedness, greater than or equal to 91%). The Greek isolates were closely related (genetic relatedness, similar to 91%) t o the penicillin-resistant MDR clone of serotype 6B that spread from Spain to Iceland in the late 1980s. Moreover, the Greek group of isolates was gen etically distinct (genetic relatedness, less than or equal to 83%) from oth er penicillin-susceptible or -resistant serotype 6B strains from various pa rts of the world. All serotype 6B penicillin-susceptible MDR isolates displ ayed a penicillin-susceptible PBP 1A-2B-2X genotype. Our findings suggest t hat the penicillin-susceptible MDR 6B clone that was found in Greece betwee n the years 1996 and 1999 represents the ancestor of the pandemic penicilli n-resistant MDR clone 6B.