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J. Bacteriol., 07 1995, 3631-3640, Vol 177, No. 13
TR Paul, A Venter, LC Blaszczak, TR Parr Jr, H Labischinski and TJ Beveridge
Precise localization of penicillin-binding protein (PBP)-antibiotic
complexes in a methicillin-sensitive Staphylococcus aureus strain (BB255),
its isogenic heterogeneous methicillin-resistant transductant (BB270), and
a homogeneous methicillin-resistant strain (Col) was investigated by
high-resolution electron microscopy. A mercury- penicillin V (Hg-pen V)
derivative was used as a heavy metal-labeled, electron-dense probe for
accurately localizing PBPs in situ in single bacterial cells during growth.
The most striking feature of thin sections was the presence of an
abnormally large (17 to 24 nm in width) splitting system within the thick
cross walls or septa of Hg-pen V- treated bacteria of all strains.
Untreated control cells possessed a thin, condensed splitting system, 7 to
9 nm in width. A thick splitting system was also distinguishable in
unstained thin sections, thereby confirming that the electron contrast of
this structure was not attributed to binding of bulky heavy metal stains
usually used for electron microscopy. Biochemical analyses demonstrated
that Hg-pen V bound to isolated plasma membranes as well as sodium dodecyl
sulfate- treated cell walls and that two or more PBPs in each strain bound
to this antibiotic. In contrast, the splitting system in penicillin V-
treated bacteria was rarely visible after 30 min in the presence of
antibiotic. These findings suggest that while most PBPs were associated
with the plasma membrane, a proportion of PBPs were located within the
fabric of the cell wall, in particular, in the splitting system. Inhibition
of one or more high-M(r) PBPs by beta-lactam antibiotics modified the
splitting system and cross-wall structure, therefore supporting a role for
these PBPs in the synthesis and architectural design of these structures in
S. aureus.
Copyright © 1995, American Society for Microbiology
Localization of penicillin-binding proteins to the splitting system of Staphylococcus aureus septa by using a mercury-penicillin V derivative
Department of Microbiology, College of Biological Science, University of Guelph, Ontario, Canada.
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