Dissemination of community-acquired methicillin-resistant Staphylococcus aureus clones in northern Norway: sequence types 8 and 80 predominate - PubMed (original) (raw)

Dissemination of community-acquired methicillin-resistant Staphylococcus aureus clones in northern Norway: sequence types 8 and 80 predominate

Anne-Merethe Hanssen et al. J Clin Microbiol. 2005 May.

Abstract

Increasing frequencies of community-acquired methicillin-resistant Staphylococcus aureus (MRSA) strain isolation have been reported from many countries. The overall prevalence of MRSA in Norway is still very low. MRSA isolates (n = 67) detected between 1995 and 2003 in northern Norway were analyzed by pulsed-field gel electrophoresis, multilocus sequence typing, and staphylococcal cassette chromosome mec (SCCmec) typing. Sixty-seven isolates were associated with 13 different sequence types. Two successful MRSA clones predominated. Sequence type 8 (ST8) (40%) and ST80 (19%) containing SCCmec type IV were detected in hospitals and communities in different geographic regions during a 7-year period. In general, there was a low level of antimicrobial resistance. Only 26% of the isolates were multiresistant. International epidemic clones were detected. The frequent findings of SCCmec type IV (91%) along with heterogeneous genetic backgrounds suggest a horizontal spread of SCCmec type IV among staphylococcal strains in parallel with the clonal spread of successful MRSA strains.

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Figures

FIG. 1.

FIG. 1.

PFGE dendrograms representing the genetic relatedness of 26 ST8-MRSA isolates (left) and 13 ST80-MRSA isolates (right). Included are also the five international MRSA clones (Brazilian, Hungarian, pediatric, Iberian, and New York/Japan clones) and the reference strains N315, NCTC 10442, 85/2082, and NCTC 8325. PFGE patterns were analyzed both visually and using GelCompar II version 2.5 (Applied Maths, Belgium). The Dice coefficient was calculated using a position tolerance of 1.5%, and the PFGE dendrograms were constructed using the unweighted pair group method with arithmetic means. Isolates that shared 95% similarity on the arithmetic mean dendrogram were considered to have the same PFGE type. The PFGE types were also defined on the basis of the DNA banding patterns by following the criteria of Tenover et al. (35) for bacterial strain typing. Strains differing by four to six fragments were considered to be subtypes of a given clonal type. The strain identifier, ST, year of isolation, and PFGE types are shown to the right. A low-range PFGE ladder (New England Biolabs, Beverly, MA) was used as the molecular size marker. The scale bar at the top of the dendrogram represents similarity.

FIG. 1.

FIG. 1.

PFGE dendrograms representing the genetic relatedness of 26 ST8-MRSA isolates (left) and 13 ST80-MRSA isolates (right). Included are also the five international MRSA clones (Brazilian, Hungarian, pediatric, Iberian, and New York/Japan clones) and the reference strains N315, NCTC 10442, 85/2082, and NCTC 8325. PFGE patterns were analyzed both visually and using GelCompar II version 2.5 (Applied Maths, Belgium). The Dice coefficient was calculated using a position tolerance of 1.5%, and the PFGE dendrograms were constructed using the unweighted pair group method with arithmetic means. Isolates that shared 95% similarity on the arithmetic mean dendrogram were considered to have the same PFGE type. The PFGE types were also defined on the basis of the DNA banding patterns by following the criteria of Tenover et al. (35) for bacterial strain typing. Strains differing by four to six fragments were considered to be subtypes of a given clonal type. The strain identifier, ST, year of isolation, and PFGE types are shown to the right. A low-range PFGE ladder (New England Biolabs, Beverly, MA) was used as the molecular size marker. The scale bar at the top of the dendrogram represents similarity.

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