Molecular Analysis by Pulsed-Field Gel Electrophoresis and Antibiogram of Streptococcus pneumoniae Serotype 6B Isolates from Selected Areas within the United States

Abstract

ABSTRACT 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 these isolates were assigned to 10 antibiotic profiles based on their susceptibilities to penicillin, erythromycin, tetracycline, and trimethoprim-sulfamethoxazole. Thirty-two (55%) of these isolates were penicillin nonsusceptible, while 21 (36%) were intermediate or resistant to three or more antibiotics. The restriction endonucleases Apa I and Sma I were used to digest intact chromosomes, and the fragments were resolved by pulsed-field gel electrophoresis (PFGE). The Apa I and Sma I PFGE patterns were combined, and 13 of the 16 Alaskan isolates showed indistinguishable PFGE patterns. One other isolate exhibited highly related Apa I and Sma I PFGE patterns, differing by only one band after restriction with Apa I. Among the 14 isolates from Arizona, 1 was indistinguishable from the predominant Apa I and Sma I PFGE patterns seen in the Alaskan isolates; 5 others were highly related (±1 band after cutting with either enzyme) to the Alaskan isolates, suggesting a common ancestral origin. Of the remaining eight isolates, six additional Apa I plus Sma I PFGE patterns were observed. The 28 isolates from the various contiguous states had 22 Apa I plus Sma I PFGE patterns. No correlations were found between specific PFGE patterns, antibiograms, dates of isolation, or geography. The serotype 6B isolates across the contiguous United States were genetically diverse, while the 6B isolates from Alaska appeared to be much less diverse.