MOLECULAR ANALYSIS BY PULSED-FIELD GEL-ELECTROPHORESIS AND ANTIBIOGRAM OF STREPTOCOCCUS-PNEUMONIAE SEROTYPE 6B ISOLATES FROM SELECTED AREASWITHIN THE UNITED-STATES

Fifty-eight clinical isolates of Streptococcus pneumoniae serotype 6B, including 16 from Alaska, 14 from Arizona, 11 from Washington, and 17 from seven additional states, were analyzed, The antibiograms of thes e isolates were assigned to 10 antibiotic profiles based on their susc eptibilities to penicillin, erythromycin, tetracycline, and trimethopr im-sulfamethoxazole. Thirty-two (55%) of these isolates were penicilli n nonsusceptible, while 21 (36%) were intermediate or resistant to thr ee or more antibiotics, The restriction endonucleases ApaI and SmaI we re used to digest intact chromosomes, and the fragments were resolved by pulsed-field gel electrophoresis (PFGE). The ApaI and SmaI PFGE pat terns were combined, and 13 of the 16 Alaskan isolates showed indistin guishable PFGE patterns. One other isolate exhibited highly related Ap aI and SmaI PFGE patterns, differing by only one band after restrictio n with ApaI. Among the 14 isolates from Arizona, 1 was indistinguishab le from the predominant ApaI and SmaI PFGE patterns seen in the Alaska n isolates; 5 others were highly related (al band after cutting with e ither enzyme) to the Alaskan isolates, suggesting a common ancestral o rigin. Of the remaining eight isolates, six additional ApaI plus SmaI PFGE patterns were observed. The 28 isolates from the various contiguo us states had 22 ApaI plus SmaI PFGE patterns. No correlations were fo und between specific PFGE patterns, antibiograms. dates of isolation, or geography. The serotype 6B isolates across the contiguous United St ates were genetically diverse, while the 6B isolates from Alaska appea red to be much less diverse.