Blood Agar


Blood agar contains 5% sheep blood, is used to grow fastidious organisms, and can differentiate between different species based on their hemolytic properties.  Many of these fastidious organisms require particular nutrients found in blood and are considered more difficult to grow.  Blood agar is considered a differential agar and can be used to differentiate between different Strep spp.



 Streak plate of Streptococcus pyogenes (incubated @ 37 degrees C for 48 hrs) showing beta hemolysis due to hemolysin O and S, complete lysis of red blood cells, around the isolated colonies. Image taken using transmitted light.  S. pyogenes causes Strep throat.



Streak plate isolation of Streptococcus mitis on blood agar demonstrating alpha hemolysis seen as a greenish color around the growing colonies due to a reduction of the hemoglobin, oxidation of iron in the hemoglobin,  to methemoglobin in the surrounding agar. Image taken using transmitted light.




Enterococcus faecalis grown on blood agar for 48 hrs at 37 degree's C. Small, pin point, circular colonies can be seen with gamma hemolysis (no hemolysis of the blood agar). Colonies were white with a glossy translucent appearance.



(a)


(b)
(a)  Three organisms inoculated onto blood agar, straight line inoculation, to demonstrate hemolysis. From top to bottom: Streptococcus pyogenes: beta, complete lysis of red blood cells, clear area around colony growth. Streptococcus bovis: alpha, incomplete lysis of red blood cells, green area around colony growth. Enterococcus faecalis: gamma, growth with no blood cell lysis. Image taken using transmitted light.
(b)  Close up of S. pyogenes showing beta hemolysis and a zone of clearing around the growing colonies




Bacitracin test done on a lawn of Streptococcus pyogenes grown on blood agar. The zone of inhibition around the bacitracin disc, approx 14mm measuring the entire length of the zone, indicates sensitivity. The zone of inhibition is red because the red blood cells did not lyse. Grown for 24 hrs at 37 degree's C.  The bacitracin test can help differentiate S. pyogenes from other Strep or Staphylococcus spp.






Tee Shirt available at Cabrillo College Book Store(831479-6209
or
Niles Biological:  http://www.nilesbio.com/cat499.html 



All images copyright Sturm

Comments

Post a Comment

Popular posts from this blog

Image
  Basic Bacterial Morphology  Bacteria and fungus (mold and yeast) grow in a variety of shapes, sizes and colors.  Although it is difficult to make a definite identification of cultures growing in broth or solid media many have distinguishing characteristics that give us clues to identification.  Many Microbiologist can make a tentative identifications by growth characteristics but definitive id requires further testing (ie Gram stain, chemical testing, etc). The palm of a hand print print done on TSA agar.  There is a mix of different textured and colored colonies on the plate some bacterial some yeast.  By looking at color, texture, growth times and various growth temperatures you can get an idea as to what is on the plate.  Ex:  the orange colonies are yeast and tend to grow better at room temperature or refrigerated temperatures where the large colony on the left ( Bacillus spp) and the white colonies ( Staphylococcus ) grows well at body temperature.  Further testing need
Read more
Image
Oxygen Requirements:  Fluid  Thioglycolate Media A                             B                                C                                      D                                E    Organisms grown in Fluid Thioglycollate Media, a reducing media that uses sodium thioglycolate to chemically combine with dissolved oxygen to deplete the oxygen in the media. The top portion of the tube contains oxygen while the bottom of the tube is lacking molecular oxygen.  All organism except for  Neisseria sicca  were grown for 48 hours at 37 o  C. Neisseria sicca  was grown for 72 hours at 37 o  C for best results.  Note: Both  N. sicca  and  C. butrycium  were grow in supplemented Thioglycollate Media.  A calcium chip can be seen in the bottom of the tube for  N. sicca which is used as a buffer.  This media is aslo supplemented with vitamin K.   Note:  I buy prepared thioglycolate media and many times the media is "jostled" in shipping.  I will autoclave the tubes to d
Read more
Image
Nitrate Reduction/Nitrate Reductase Test Some bacterial species are able to reduce nitrate (NO3)  to nitrite (NO2)  using the enzyme nitrate reductase in an anaerobic process by using molecules other then oxygen, nitrate, as a terminal electron acceptor.  To determine if a bacteria is able to reduce nitrate they are grown in a nitrate broth and a series of chemical are added to detect nitrate reduction. (A)                                                 (B)                                                     (C)      Nitrate reduction test for the reduction of nitrate in nitrate media, to determine if the bacteria contains nitrate and/or nitrite reductase. Organism were incubated for 48 hr's at 37 degree's in nitrate media then reagents added.  The addition of these reagents test for the presence of nitrites and the media will turn red if nitrites are present. Nitrate broths after the addition of 10 drops reagents A (sulfanilic acid in acetic acid) and B (nn-di
Read more