Mediterranean clone of penicillin-susceptible, multidrug-resistant serotype 6B Streptococcus pneumoniae in Greece, Italy and Israel

In 1996, 19 isolates of serotype 6B Streptococcus pneumoniae with a unique resistance pattern were found in carriers attending daycare centres in Patras, Southwestern Greece. These isolates were penicillin susceptible but resistant to chloramphenicol, tetracycline, erythromycin, clindamycin and trimethoprim-sulphamethoxazole. Subsequently, isolates with the same characteristics were found in 23 additional carriers in central and southern Greece in 1997-98 as well as in 19 carriers in central Italy in 1997, and in seven carriers in southern Israel in 1998. Carriers were all children under 6 years of age, attending daycare centres or outpatient hospital visits. The relatedness of the isolates was determined on representative isolates from the three countries by pulsed-field gel electrophoresis of SmaI digests of chromosomal DNA. Most Greek isolates were identical to each other, while isolates from Italy and Israel showed one to three band differences, with all isolates being closely related to each other as well as to the isolates from Greece. We have therefore documented the presence of this unique clone of S. pneumoniae in these three countries and have named this the 'Mediterranean' clone. While isolates appear to have a common origin, their source and direction of spread are unknown. However, isolates from Italy showed the most diversity, suggesting that this clone had been present in that country for a longer period than it had been in Greece.