Assignment of a strain to the genus Staphylococcus requires it to be a Gram-positive coccus that forms clusters, produces catalase, has an appropriate cell wall structure (including peptidoglycan type and teichoic acid presence) and G + C content of DNA in a range of 30–40 mol%.
Staphylococcus species can be differentiated from other aerobic and facultative anaerobic, Gram-positive cocci by several simple tests. Staphylococcus spp. are facultative anaerobes (capable of growth both aerobically and anaerobically). All species grow in the presence of bile salts.
It was believed that all species were catalase-positive however it is now known that not all Staphylococcus are coagulase positive.
Growth can also occur in a 6.5% NaCl solution. On Baird Parker medium, Staphylococcus spp. grow fermentatively, except for S. saprophyticus, which grows oxidatively. Staphylococcus spp. are resistant to bacitracin (0.04 U disc: resistance = <10mm zone of inhibition) and susceptible to furazolidone (100μg disc: resistance = <15mm zone of inhibition). Further biochemical testing is needed to identify to the species level.
When the bacterium divides it divides along two axes, so forming clumps of bacteria. This is as opposed to streptococci which divide along one axis and so form chains (strep. meaning twisted or pliant).
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