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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 aureus (/ ˌ s t æ f ɪ l ə ˈ k ɒ k ə s ˈ ɔːr i ə s,-l oʊ-/, [16] [17] Greek σταφυλόκοκκος ' grape-cluster berry ', Latin aureus, ' golden ') is a facultative anaerobic, gram-positive coccal (round) bacterium also known as "golden staph" and "oro staphira".
It is used to isolate Staphylococcus aureus from clinical specimens and food. It was first described by Vogel and Johnson, who modified the Tellurite Glycine Agar recipe by Zebovitz et al. by doubling the mannitol concentration to 1% (w/v) and adding Phenol red as a pH indicator. [1] It is widely available commercially.
Importantly, S. aureus is generally coagulase-positive, meaning that a positive coagulase test would indicate the presence of S. aureus or any of the other 11 coagulase-positive Staphylococci. [1] A negative coagulase test would instead show the presence of coagulase-negative organisms such as S. epidermidis or S. saprophyticus.
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]
Examining colonial morphology is the first step in the identification of an unknown microbe. The systematic assessment of the colonies' appearance, focusing on aspects like size, shape, colour, opacity, and consistency, provides clues to the identity of the organism, allowing microbiologists to select appropriate tests to provide a definitive ...
Illustration of streak plate procedure to achieve isolated colonies using aseptic technique. The three-phase streaking pattern, also known as the T-Streak, is recommended for beginners. [5] However it is also limited in applications using greater than a single culture. [5] The plate is split by drawing a "T" to create three separate sections.
S. aureus is also implicated [6] in toxic shock syndrome; during the 1980s some tampons allowed the rapid growth of S. aureus, which released toxins that were absorbed into the bloodstream. Any S. aureus infection can cause the staphylococcal scalded skin syndrome , a cutaneous reaction to exotoxin absorbed into the bloodstream.