Clonal distribution of invasive Neisseria meningitidis isolates from the Norwegian county of Telemark, 1987 to 1995

Abstract

Forty-two Neisseria meningitidis isolates were obtained from patients with meningococcal disease in the Norwegian county of Telemark (January 1987 to March 1995), and all were compared by PCR amplicon restriction endonuclease analysis (PCR-AREA) of the dhps gene, chromosomal DNA fingerprinting, and serological analysis. PCR-AREA divided the isolates into 11 classes, of which 4, comprising 15, 8, 6, and 2 isolates, were clonal while the remaining 8 classes were genetically heterogeneous or contained only 1 isolate. Three of the four clonal classes could be tentatively equated with recognized epidemic clones (ET5, ET37, and cluster A4) on the basis of their phenotypic characteristics, while the remaining clone appears to be new. There were significant differences in the geographical distribution of clones, with class 1 (ET5-like) isolates significantly overrepresented in rural parts of Telemark. Class 1 (ET5-like) isolates occurred throughout the study period and were dominant in 1987. Class 2 (ET37-like) isolates occurred from 1988 to 1992, and class 3 isolates (with no recognizable ET affinities) were found only in 1991 and 1992.

FIG. 1

PCR-AREA of N. meningitidis isolates from Telemark showing the 11 different CfoI digestion patterns. Lane numbers correspond to the class number. The size standards (Std) are U.S. Biochemicals PCR molecular size markers, with fragment sizes of 1,000, 700, 525, 500, 400, 300, 200, 100, and 50 bp.

FIG. 2

Typical PCR-AREA gel showing classes 1, 2, 4, and 5. The lanes are numbered according to the class. The standard (St) is a mixture of PCR products and restriction fragments. Fragment sizes are 645, 217, 100, 83, 74, and 62 bp.

FIG. 3

Temporal distribution of PCR-AREA classes from 1987 to 1995.