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Antimicrobial Agents and Chemotherapy, February 1998, p. 306-312, Vol. 42, No. 2
Departments of
Medicine1 and
Microbiology/Immunology,2 Medical College of
Virginia, Virginia Commonwealth University, Richmond, Virginia
23298-0049
Received 16 July 1997/Returned for modification 20 September
1997/Accepted 20 November 1997
mecA, the gene that mediates methicillin resistance,
and its accompanying mec locus DNA, insert near the
gyrA gene in Staphylococcus aureus. To
investigate whether there is a similar relationship between
mecA and gyrA in coagulase-negative
staphylococci (CNS), mecA- and gyrA-specific
DNA fragments were used to probe methicillin-resistant isolates of
Staphylococcus epidermidis (MRSE) (n = 11)
and Staphylococcus haemolyticus (MRSH) (n = 11). The gyrA probe hybridized to the same
SmaI DNA fragment as the mecA probe in all
strains tested. However, since the size of the SmaI
fragments containing mecA and gyrA varied from
73 to 600 kb, the distance between the two genes was determined more
precisely. Cloned mecA or gyrA fragments plus
vector sequences each containing a SmaI site were
introduced into the chromosome of three isolates each of MRSE and
methicillin-resistant S. aureus (MRSA), and the sizes of
the generated SmaI fragments were determined by
pulsed-field gel electrophoresis. The distance between gyrA
and mecA was found to be between 38 and 42 kb in both MRSE
and MRSA, and the two genes were in the same relative orientation in
all strains. Restriction fragment length polymorphism (RFLP) patterns
around the gyrA gene in CNS were identical, but species
specific, for all 10 MRSE and 10 MRSH isolates examined. In contrast, 8 of 11 methicillin-susceptible S. epidermidis isolates and 7 of 7 methicillin-susceptible S. haemolyticus isolates had different gyrA RFLP patterns. These data show that
mecA is site and orientation specific, relative to
gyrA, in both MRSE and MRSA. In addition, the local
environment around gyrA in methicillin-resistant CNS, in
contrast to methicillin-susceptible isolates, is similar, suggesting
clonality or the requirement for specific DNA sequences with which the
mec complex must interact for chromosomal integration to
occur.
0066-4804/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
Determination of the Chromosomal
Relationship between mecA and gyrA in
Methicillin-Resistant Coagulase-Negative Staphylococci

*
Corresponding author. Mailing address: Division of
Infectious Diseases, Department of Medicine, Medical College of
Virginia, Box 980049, Room 7-082, Sanger Hall, 1101 E. Marshall St.,
Richmond, VA 23298-0049. Phone: (804) 828-9711. Fax: (804) 828-3097. E-mail: GARCHER{at}GEMS.VCU.EDU.
Present address: University of Nebraska Medical Center, Division of
Infectious Disease, Omaha, NE 68198.
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