  Staphylococcus aureus is a coccal bacterium, which divides by binary fission.
After division the cells remain attached giving rise to small clusters, with a
characteristic 'bunch of grapes' morphology. S. aureus is an important human
pathogen and this, combined with the increasing prevalence of
antibiotic-resistant strains, such as Methicillin Resistant S. aureus (MRSA),
make it an excellent subject for studies of new methods of antimicrobial
action. Many antibiotics, such as penicillin, prevent S. aureus cell division
and so an understanding of this fundamental process may pave the way to the
identification of novel drugs. We present here a novel image analysis framework
for automated detection and segmentation of cells in S. aureus clusters, and
identification of their cell division planes. We demonstrate the technique on
GFP labelled EzrA, a protein that localises to a mid-cell plane during division
and is involved in regulation of cell size and division. The algorithms may
have wider applicability in detecting morphologically complex structures of
fluorescently-labelled proteins within cells in other cell clusters.
