Affiliation:
1. Departments ofMedicine1 and
2. Microbiology/Immunology,2 Medical College of Virginia, Virginia Commonwealth University, Richmond, Virginia 23298-0049
Abstract
ABSTRACT
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
Sma
I DNA fragment as the
mecA
probe in all strains tested. However, since the size of the
Sma
I 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
Sma
I site were introduced into the chromosome of three isolates each of MRSE and methicillin-resistant
S. aureus
(MRSA), and the sizes of the generated
Sma
I 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.
Publisher
American Society for Microbiology
Subject
Infectious Diseases,Pharmacology (medical),Pharmacology
Cited by
13 articles.
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