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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".
Resistance to antibiotics in S. aureus can be quantified by determining the amount of the antibiotic that must be used to inhibit growth. If S. aureus is inhibited at a concentration of vancomycin less than or equal to 4 μg/ml, it is said to be susceptible. If a concentration greater than 32 μg/ml is necessary to inhibit growth, it is said to ...
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.
The first S. aureus genomes to be sequenced were those of N315 and Mu50, in 2001. Many more complete S. aureus genomes have been submitted to the public databases, making it one of the most extensively sequenced bacteria. The use of genomic data is now widespread and provides a valuable resource for researchers working with S. aureus.
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.
The hemolysis of some weakly beta-hemolytic organisms is enhanced when streaked close to certain beta hemolytic strains of Staphylococcus aureus. This phenomenon is the mechanism behind the CAMP test , [ 2 ] a test that was historically used for the identification of Streptococcus agalactiae and Listeria monocytogenes . [ 3 ]
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