Abstract
In developed countries, blood agar containing defibrinated sheep or horse blood is a standard tool for the isolation of bacteria from clinical samples. Several issues prevent blood agar containing animal blood from being used in many developing countries. However, the use of easily available human blood for blood agar is discouraged because of the common tenet that human blood in nutrient media results in poor bacterial isolation rates and hardly visible hemolysis or no hemolysis at all. We have developed a reconfigured and easily applicable composition for blood agar containing human blood and tested its usability with respect to hemolysis visibility and its characteristics in antibiograms with Streptococcus spp. Hemolysis tests were conducted with clinical strains of Staphylococcus aureus, Streptococcus dysgalactiae, and Streptococcus mitis. In a second test series, clinical strains of Streptococcus dysgalactiae, Streptococcus agalactiae, and Streptococcus mitis were tested with Mueller-Hinton agars containing defibrinated wether blood as well as with Mueller-Hinton agars containing citrated human blood to compare the results of antibiotic susceptibility testing. The reconfigured blood agars containing 2.5% citrated human blood showed almost identical reactions to the standard blood agars used in the developed world. For the first time, blood agars containing 2.5% citrated human blood were shown to be an acceptable alternative for the isolation of the above-mentioned bacteria as well as for use in antibiotic susceptibility testing.
Highlights
In developed countries, blood agar containing defibrinated sheep or horse blood is a standard tool for the isolation of bacteria from clinical samples
The common tenet is that human blood in nutrient media results in poor bacterial isolation rates and in hardly visible hemolysis or no hemolysis at all [3,5]
To compare the visibility of hemolysis on the different media, one colony of each bacterial family was streaked in duplicate on three types of agar with an inoculation loop: (1) Columbia agar enriched with 5% defibrinated sheep blood as a reference standard; (2) Columbia agar enriched with 5% citrated human blood; and (3) Columbia agar enriched with 2.5% citrated human blood, the reconfigured nutrient medium
Summary
Blood agar containing defibrinated sheep or horse blood is a standard tool for the isolation of bacteria from clinical samples. The use of available human blood for blood agar is discouraged because of the common tenet that human blood in nutrient media results in poor bacterial isolation rates and hardly visible hemolysis or no hemolysis at all. The gold standard for diagnosing hemolyzing bacteria such as beta-hemolytic Staphylococcus aureus and beta-hemolytic Streptococcus spp. is cultivating these organisms on solid culture media containing a source of blood that can be hemolyzed. To prepare this blood agar, defibrinated sheep, goat, pig or horse blood in a concentration of 5% [1-3] is recommended. Blood bags often contain citric acid, which is a well-known bacteriostatic agent
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