Often asked: Why Is Sheep Blood Agar Classified As Differential Media And Not Selective?

Why is blood agar considered a differential and not selective?

Blood agar is differential media because 3 different types of hemolysis, or lysing of red blood cells, can be seen on this plate.

Is sheep blood agar both selective and differential?

Blood agar (BAP) is a differential growth medium which microbiologists use to distinguish clinically significant bacteria from throat and sputum cultures. BAP contains 5% sheep blood. Certain bacteria produce exotoxins called hemolysins, which act on the red blood cells to lyse, or break them down.

Why is sheep blood agar a differential medium?

Examples include sheep blood agar and chocolate (heated blood) agar. Selective media contain ingredients that inhibit the growth of some organisms but allow others to grow. Blood agar is one type of differential medium, allowing bacteria to be distinguished by the type of hemolysis produced (see below).

Is sheep blood agar selective?

BD Group A Selective Strep Agar with 5% Sheep Blood (ssA™) is a selective medium for use in the isolation and presumptive identification of group A streptococci from throat cultures and other clinical specimens.

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What is the difference between selective and differential agar?

Selective media favor the growth of some microorganisms while inhibiting others. Differential media help distinguish bacteria by the color of the colonies or the change in the medium.

What makes MacConkey agar both selective and differential?

This medium is both selective and differential. The selective ingredients are the bile salts and the dye, crystal violet which inhibit the growth of Gram-positive bacteria. The differential ingredient is lactose.

Is chocolate agar selective or differential?

Chocolate agar, a differential medium for gram-positive cocci.

Is MSA selective or differential?

Mannitol Salt Agar (MSA) This type of medium is both selective and differential. The MSA will select for organisms such as Staphylococcus species which can live in areas of high salt concentration (plate on the left in the picture below).

What type of bacteria grow on blood agar?

Blood Agar is used to grow a wide range of pathogens particularly those that are more difficult to grow such as Haemophilus influenzae, Streptococcus pneumoniae and Neisseria species. It is also required to detect and differentiate haemolytic bacteria, especially Streptococcus species.

What ingredient in sheep blood agar makes the Medium differential?

The CNA-blood agar, like the TSA-blood agar is differential. The differential material in both is defibrinated red blood cells. Bacteria that can metabolize whole RBC’s do so by producing the enzyme hemolysin.

What organisms are inhibited from growing on MSA?

It contains a high concentration (about 7.5–10%) of salt (NaCl) which is inhibitory to most bacteria – making MSA selective against most Gram-negative and selective for some Gram-positive bacteria ( Staphylococcus, Enterococcus and Micrococcaceae) that tolerate high salt concentrations.

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What bacteria does not grow on blood agar?

Fastidious organisms, such as streptococci, do not grow well on ordinary growth media but grow on blood agar.

What types of bacteria grow on nutrient agar?

Nutrient agar provides these resources for many types of microbes, from fungi like yeast and mold to common bacteria such as Streptococcus and Staphylococcus.

Is pea agar selective or differential?

PEA agar is a selective medium that permits the growth of gram-positive cocci while inhibiting most gram-negative organisms.

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