The TOT layers in turn consist of two tetrahedral sheets (T) strongly bonded to the two faces of a single trioctahedral sheet (O). It is the weak bonding between TOT layers that gives talc its perfect basal cleavage and softness.The tetrahedral sheets consist of silica tetrahedra, which are silicon ions surrounded by four oxygen ions. The tetrahedra each share three of their four oxygen ions with neighboring tetrahedra to produce a hexagonal sheet. The remaining oxygen ion (the apical oxygen ion) is available to bond with the trioctahedral sheet.The trioctahedral sheet has the structure of a sheet of the mineral brucite. Apical oxygens take the place of some of the hydroxyl ions that would be present in a brucite sheet, bonding the tetrahedral sheets tightly to the trioctahedral sheet.Tetrahedral sheets have a negative charge, since their bulk composition is Si4O104-. The trioctahedral sheet has an equal positive charge, since its bulk composition is Mg3(OH)24+ The combined TOT layer thus is electrically neutral.Because the hexagons in the T and O sheets are slightly different in size, the sheets are slightly distorted when they bond into a TOT layer. This breaks the hexagonal symmetry and reduces it to monoclinic or triclinic symmetry. However, the original hexahedral symmetry is discernible in the pseudotrigonal character of talc crystals. Occurrence
Talc is a common metamorphic mineral in metamorphic belts that contain ultramafic rocks, such as soapstone (a high-talc rock), and within whiteschist and blueschist metamorphic terranes.
Staphylococci that are resistant to methicillin and oxacillin should also be considered clinically resistant to cefoxitin even if they test susceptible by in vitro methods.Major bacterial strains susceptible to cefoxitin include:
methicillin-susceptible Staphylococcus aureus
Streptococcus sp. E. coli
Salmonella sp. Proteus vulgaris
Flavobacterium sp. Klebsiella sp.Major bacteria resistant to cefoxitin include:
methicillin-resistant Staphylococcus aureus
Enterococci
Listeria monocytogenes
Enterobacter sp. Bacteroides sp. Replacement and substitution
In a 2005 study, Fernandes et al. determined that cefoxitin serves as an appropriate replacement for methicillin in determining if some bacteria display methicillin resistance. Likewise, Funsun et al. found in a 2009 study that cefoxitin disk assays correctly identified all 60 mecA-positive Staphylococcus aureus, or MRSA isolates, to be resistant to cefoxitin.Due, in part, to the unavailability of methicillin in the United States, cefoxitin has replaced methicillin for disk diffusion tests, which determine the sensitivity of a bacterial specimen to a given antibiotic. Cefoxitin also yields more accurate results for disk diffusion tests. Interpretive criteria for determining susceptibility to cefoxitin via disk diffusion are greater than or equal to 22mm resulting in a "susceptible" result for Staphylococcus aureus and greater than or equal to 25mm for coagulase-negative staphylococci to be considered susceptible.The following are susceptibility data for several medically significant microorganisms, measured by minimum inhibitory concentration, which is an alternative, liquid medium test for susceptibility. Escherichia coli: 0.2 μg/ml – 64 μg/ml
Haemophilus influenzae: 0.5 μg/ml – 12.5 μg/ml
Streptococcus pneumoniae: 0.2 μg/ml – 1 μg/ml

Uses in medicine
Cefoxitin is sold in three major IV doses, 1g, 2g, and 10g.