Blood Agar Bacterial Growth Medium: Alpha, Beta & Gamma Hemolysis

This video provides photos and narrator interpretation of Blood Agar (BAP) specialized bacterial growth medium. Examples of sterile BAP as well as plates with growth of normal flora (gamma and alpha hemolytic bacteria) are contrasted with the presence of beta hemolytic Streptococcus pyogenes.

This video provides complete information on how to determine if bacteria exhibiting beta hemolysis on BAP are Streptococcus pyogenes. There are other types of bacteria that are beta hemolytic, however S. pyogenes will grow in punctiform (tiny round) creamy white colonies.

S. pyogenes is a Gram-positive, beta hemolytic bacteria. There are also Gram-negative beta hemolytic bacteria, but their colony morphology is different than that of S. pyogenes. B-hemolytic Gram-negatives grow in comparatively large colonies that are round, flat and greyish or neutral in color. There will also not typically be many Gram-negative bacteria present in a throat sample (the type of BAP clinical sample shown in this video).

By Tami (Guy) Port, Chief Executive Nerd at ScienceProfOnline.com. For the lab materials that go with this movie, see the Virtual Microbiology Classroom Media and Culture Laboratory Main Page at ScienceProfOnline.com.