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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]
The carriage of S. aureus is an important source of hospital-acquired infection (also called nosocomial) and community-acquired MRSA. Although S. aureus can be present on the skin of the host, a large proportion of its carriage is through the anterior nares of the nasal passages [2] and can further be present in the ears. [133]
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.
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.
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
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]
The diagnosis of vancomycin-resistant Staphylococcus aureus (VRSA) is performed by performing susceptibility testing on a single S. aureus isolate to vancomycin. This is accomplished by first assessing the isolate's minimum inhibitory concentration (MIC) using standard laboratory methods, including disc diffusion, gradient strip diffusion, and automated antimicrobial susceptibility testing ...