JAC Advance Access originally published online on May 7, 2008
Journal of Antimicrobial Chemotherapy 2008 62(2):324-328; doi:10.1093/jac/dkn186
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Original research |
Recurrence of heterogeneous methicillin-resistant Staphylococcus aureus (MRSA) among the MRSA clinical isolates in a Japanese university hospital
1 Department of Infection Control Science, Juntendo University, 2-1-1 Hongo, Bunkyo-ku, Tokyo 113-8421, Japan 2 Department of Bacteriology, Juntendo University, 2-1-1 Hongo, Bunkyo-ku, Tokyo 113-8421, Japan 3 Department of Medical Safety Administration, Division of Infection Control, Dokkyo University Hospital, Shimotsuga-gun, Tochigi 321-0293, Japan
Received 9 August 2007; returned 12 December 2007; revised 30 March 2008; accepted 31 March 2008
* Corresponding author. Tel: +81-3-5802-1041; Fax: +81-3-5684-7830; E-mail: kozuwe{at}med.juntendo.ac.jp
Objectives: In the early 1980s, heterogeneous methicillin-resistant Staphylococcus aureus (hetero-MRSA) strains were predominant in the University of Tokyo Hospital. But, in the 1990s, they were completely substituted by homogeneously highly methicillin-resistant S. aureus (homo-MRSA) strains. Since 2000, however, we started observing an increase in MRSA strains with low cefazolin MICs (MRCLSA). This study was performed to understand the phenomenon by characterization of the ‘cefazolin-susceptible’ MRSA strains.
Methods: A total of 39 MRCLSA strains were collected between July 2000 and June 2002 and compared with 10 homo-MRSA strains isolated during the same period for their antibiograms and genotypes. The strains were also compared with the hetero-MRSA strains isolated in the same hospital in the early 1980s.
Results: In contrast to the homogeneous genotype [multilocus sequence type 5 and SCCmec type II.1 (IIa)] and multiresistant nature of the homo-MRSA strains, the MRCLSA strains were composed of various genotypes as revealed by multilocus sequence typing and SCCmec typing and had resistance only to a limited number of antibiotics. Most of the MRCLSA strains were also genetically differentiated from the hetero-MRSA strains of the 1980s. However, population analysis revealed that all of the MRCLSA strains were classified as hetero-MRSA strains.
Conclusions: A new group of hetero-MRSA strains genetically distinct from those dominant in the same hospital in the early 1980s might have emerged in the community and started invading the university hospital. This phenomenon may be caused by the change in the pattern of antibiotic use.
Keywords: community-associated MRSA , healthcare-associated MRSA , β-lactam antibiotics , population analysis