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An MSA plate with Micrococcus sp. (1), Staphylococcus epidermidis (2) and S. aureus colonies (3). Mannitol salt agar or MSA is a commonly used selective and differential growth medium in microbiology. It encourages the growth of a group of certain bacteria while inhibiting the growth of others. [1]
Staphylococcus epidermidis, 1000 magnification under bright field microscopy. Staphylococcus epidermidis is a very hardy microorganism, consisting of nonmotile, Gram-positive cocci, arranged in grape-like clusters. It forms white, raised, cohesive colonies about 1–2 mm in diameter after overnight incubation, and is not hemolytic on blood agar ...
For example, if a microbiologist observes colonies that resemble a Staphylococcus species, they may perform a catalase test to confirm that it belongs to the genus Staphylococcus, and a coagulase test to determine whether it is a coagulase-negative staphylococcus or a more pathogenic species, such as S. aureus. [3]: 101 [8]: 203
Nutrient agar is a general-purpose solid medium supporting growth of a wide range of non-fastidious organisms. It typically contains (mass/volume): [1] 0.5% peptone - this provides organic nitrogen; 0.3% beef extract/yeast extract - the water-soluble content of these contribute vitamins, carbohydrates, nitrogen, and salts; 1.5% agar - this ...
PNP Agar is an agar medium used in microbiology to identify Staphylococcus species that have phosphatase activity. The medium changes color when p-nitrophenylphosphate disodium (PNP) is dephosphorylated. [1] PNP agar is composed of Mueller–Hinton agar buffered to pH 5.6 to 5.8, with the addition of 0.495 mg/mL PNP. [2]
If an organism does not induce hemolysis, the agar under and around the colony is unchanged and the organism is called non-hemolytic or said to display gamma-hemolysis (γ-hemolysis). Enterococcus faecalis (formerly called "Group D Strep"), Staphylococcus saprophyticus, and Staphylococcus epidermidis display gamma-hemolysis.
The plates are incubated for 12 hours up to several days, depending on the test that is performed. Commonly used types of agar plates include: Red blood cells on an agar plate are used to diagnose infection. On the left is a positive Staphylococcus infection, on the right a positive Streptococcus culture.
Staphylococcus growth in Baird-Parker (BP) agar.. Baird-Parker agar is a type of agar used for the selective isolation of gram-positive Staphylococci species. [1] It contains lithium chloride and tellurite to inhibit the growth of alternative microbial flora, while the included pyruvate and glycine promote the growth of Staphylococci. [1]