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Journal of Clinical Microbiology, April 2001, p. 1540-1548, Vol. 39, No. 4
Laboratory of Hospital Infection, Central
Public Health Laboratory, London, NW9 5HT, United
Kingdom,1 and Microbiologia, Virgin
del Campino Hospital, Pamplona, Spain2
Received 18 September 2000/Returned for modification 11 November
2000/Accepted 11 January 2001
EMRSA-15 is one of the most important strains of epidemic
methicillin-resistant Staphylococcus aureus (EMRSA) found
in the United Kingdom. It was originally characterized by weak lysis with phage 75 and production of enterotoxin C but not urease. Two
variant strains of EMRSA-15 which show a broader phage pattern than the
progenitor strain have emerged. A total of 153 recent clinical isolates
representing classical EMRSA-15 (55 isolates) or these phage variants
(98 isolates) were compared by SmaI macrorestriction profiles in pulsed-field gel electrophoresis (PFGE) as well as by
urease and enterotoxin C production. Eight of the 98 isolates were
shown to be other unrelated strains by both PFGE and their production
of urease, a misidentification rate of 8% by phage typing. Seventy-one
EMRSA-15 isolates were enterotoxin C negative, and the majority of
these were sensitive to phage 81. Examination of PFGE profiles and
Southern blotting studies suggest that the enterotoxin C gene locus is
encoded on a potentially mobile DNA segment of ca. 15 kb. After
elimination of the eight non-EMRSA-15 isolates, the remaining 145 were
characterized by PFGE, yielding 22 profiles. All profiles were within
five band differences of at least one other profile. Classical EMRSA-15
isolates showed nine PFGE profiles, with the majority of isolates
(68%) in profile B1. Six of these nine PFGE profiles were unique to
the classical EMRSA-15 isolates. Among the phage variants of EMRSA-15,
16 profiles were seen, but the majority of isolates (83%) fell into 1 of 4 profiles (B2, B3, B4, and B7) which correlated well with phage patterns. The most divergent PFGE profiles among the EMRSA-15 isolates
had as many as 12 band differences from one another, suggesting that in
examining isolates belonging to such a temporally and geographically
disseminated epidemic strain, the range of PFGE profiles must be
regarded as a continuum and analyzed by relating the profiles back to
the most common or progenitor profile.
0095-1137/01/$04.00+0 DOI: 10.1128/JCM.39.4.1540-1548.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
Identification and Characterization of Phage Variants of a
Strain of Epidemic Methicillin-Resistant Staphylococcus
aureus (EMRSA-15)
*
Corresponding author. Present address: Division of
Environmental Health and Risk Management, Public Health Building,
University of Birmingham, Birmingham B15 2TT, United Kingdom. Phone: 44 121 414 7750. Fax: 44 121 414 3078. E-mail:
g.l.oneill{at}bham.ac.uk.
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