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Description:This inoculated human blood agar culture plate cultivated colonial growth of Gram-negative, rod-shaped and facultatively anaerobic Serratia marcescens bacteria.

Note the hemolytic effect induced by the presence of the S. marcescens, which was indicated by the halo surrounding each of the bacterial colonies. In these lightened area, a lysis of red blood cells (RBCs) contained in the blood agar medium had taken place. In this case the hemolytic effect is termed beta-hemolysis (ß-hemolysis), whereupon, there is a “complete” lysis of the RBCs. Beta hemolysis is due to the bacterial production of hemolysins. There is another type of hemolytic reaction, which is known as alpha hemolysis (a-hemolysis), in which case there would be a greenish halo visible surrounding the bacterial colonies, and is sometimes referred to as “incomplete”, or “partial” hemolysis. Alpha hemolysis is brought on due to the bacterial production of peroxides.
S. marcescens is an opportunistic pathogen, which means that it is usually not a cause of disease, however, under immunocompromised circumstances this bacterium can be found the culprit responsible for nosocomial infections such as endocarditis and pneumonia. This bacterium has also been found to be an infrequent cause of nosocomial, or hospital-acquired infections.

The culturing of a new organism using differing agar media, photomicrographs, and chemical analyses are all used in the taxonomic investigative process, which results in the placement of each organism into its appropriate taxonomic niche.

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Content Providers(s):CDC/ Dr. Negut
Creation Date:1973
Photo Credit:
CDC Organization
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Copyright Restrictions:None - This image is in the public domain and thus free of any copyright restrictions. As a matter of courtesy we request that the content provider be credited and notified in any public or private usage of this image.