The genus Streptococcus includes a large and varied group of bacteria. Some are normal flora while others are pathogenic in humans. Streptococci are gram positive cocci arranged in long beadlike chains and pairs. All streptococci are catalase negative. Most grow well on sheep blood agar. Colonies are usually small, nonpigmented, and glistening. They will present on sheep blood agar with varying hemolytic degrees. Most streptococcal species associated with human disease are S. pyogenes, S. agalactiae, S. pneumoniae, viridans streptococci, and group D streptococci. Streptococci may be classified immunologically by their cell wall antigens and also by their hemolysis of red blood cells. Clinical identification is based on sensitivity to certain drugs, presence of the CAMP reaction, and other biochemical tests.

Assessment

Provide an unknown clinical specimen to the student. The student should identify the streptococcal organism in the specimen. The instructor may give several specimens to assess overall competence. The student will provide a laboratory report outlining tests performed and outcomes along with final identification of the organism.