Question: What Does Blood Agar Detect?

What does a blood agar test for?

Blood Agar Plates (BAP) BAP tests the ability of an organism to produce hemolysins, enzymes that damage/lyse red blood cells (erythrocytes).

The degree of hemolysis by these hemolysins is helpful in differentiating members of the genera Staphylococcus, Streptococcus and Enterococcus..

What bacteria can 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.

Why is blood agar used for urine culture?

CLED Agar is a differential culture medium for use in isolating and enumerating bacteria in urine. MacConkey II Agar is a selective and differential medium for the isolation and differentiation of Enterobacteriaceae and a variety of other gram-negative rods from clinical and non-clinical specimens.

Is blood agar an example of a selective medium?

Examples of enriched media 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.

What does hemolysis look like?

Hemolysis of blood samples. Red blood cells without (left and middle) and with (right) hemolysis. If as little as 0.5% of the red blood cells are hemolyzed, the released hemoglobin will cause the serum or plasma to appear pale red or cherry red in color.

What does beta hemolysis look like on blood agar?

Beta-hemolysin breaks down the red blood cells and hemoglobin completely. This leaves a clear zone around the bacterial growth. Such results are referred to as β-hemolysis (beta hemolysis). Alpha-hemolysin partially breaks down the red blood cells and leaves a greenish color behind.

What does MacConkey agar test for?

MacConkey (1861-1931). MacConkey agar is a selective and differentiating agar that only grows gram-negative bacterial species; it can further differentiate the gram-negative organisms based on their lactose metabolism.

Why is human blood not used in blood agar?

Agar prepared with human blood is not recommended, partly because of the safety risk to laboratory personnel, but mainly because it is said to result in poor bacterial isolation rates, although there are few published data to support this (2).

Why can most bacteria grow on blood agar quizlet?

Terms in this set (9) No, the only thing that grows on blood agar is the bacteria because it breaks down RBCs. Blood agar is a differential medium because all the bacteria will grow on it due to the nutrients and iron. What type of hemolysis does the bacteria infecting Patient A cause?

Can E coli grow on blood agar?

E coli is a gram-negative bacillus that grows well on commonly used media. It is lactose-fermenting and beta-hemolytic on blood agar. Most E coli strains are nonpigmented.

Why is blood agar used for streptococcus?

Blood agar is commonly used to isolate not only streptococci, but also staphylococci and many other pathogens. Besides providing enrichments for the growth of fastidious pathogens, Blood agar can be used to detect hemolytic properties.

What color is E coli on MacConkey Agar?

dark pinkPresumptive identification of E. coli was made based on its characteristic morphology colony on the selective medium MacConkey agar. Rapid lactose fermenting colonies of E. coli appear dry, donut shaped and dark pink in color and are surrounded with dark pink area of precipitated bile salts.

Why is MacConkey agar used for E coli?

Sorbitol MacConkey agar is a variant of traditional MacConkey agar used in the detection of E. coli O157:H7. … This is important because gut bacteria, such as Escherichia coli, can typically ferment lactose, while important gut pathogens, such as Salmonella enterica and most shigellas are unable to ferment lactose.

Why can most bacteria grow on blood agar?

Blood agar is an enriched medium that provides an extra rich nutrient environment for microbes. Therefore, BAP is not a selective growth medium, since it supports the growth of a wide range of organisms.

What happens to blood agar when an alpha hemolytic reaction occurs?

Alpha hemolysis is a greenish discoloration that surrounds a bacterial colony growing on the agar. This type of hemolysis represents a partial decomposition of the hemoglobin of the red blood cells. … This is a normal reaction of the blood to the growth conditions used (37° C in the presence of carbon dioxide).

What bacteria does not grow on blood agar?

Blood agar is an enriched, bacterial growth medium. Fastidious organisms, such as streptococci, do not grow well on ordinary growth media. Blood agar is a type of growth medium (trypticase soy agar enriched with 5% sheep blood) that encourages the growth of bacteria, such as streptococci, that otherwise wouldn’t grow.

What is the difference between EMB agar and MacConkey Agar?

An example of a selective medium is MacConkey agar. It contains bile salts and crystal violet, which interfere with the growth of many gram-positive bacteria and favor the growth of gram-negative bacteria. … EMB contains the dyes eosin and methylene blue that inhibit the growth of gram-positve bacteria.

What does Alpha hemolysis indicate?

Alpha-hemolysis (α-hemolysis) is a partial or “green” hemolysis associated with reduction of red cell hemoglobin. Alpha hemolysis is caused by hydrogen peroxide produced by the bacterium, oxidizing hemoglobin to green methemoglobin. … Persistence of some unhaemolysed RBC’s can be seen microscopically.