5.2 Streptococcus Flashcards
What is a general description of streptococcus?
gram positive
round bacterium
forms chains
What does it mean that strep is catalase negative?
cannot breakdown peroxides
What type of plate is strep usually cultured on?
BAP
Why is strep typically cultured on blood agar plates?
many strains; quickest and easiest way to identify and classify a potential strep microbe based on hemolytic properties
What are the three hemolytic categories on a BAP?
alpha
beta
gamma
What strain of strep shows alpha hemolysis and how does it appear?
strep pneumonia; greenish brown color
What strain of strep shows beta hemolysis and how does it appear?
strep aureus; clearing zone
What strain of strep shows gamma hemolysis and how does it appear?
enterococcus faecalis; white/tan in color
How can beta-hemolytic streps be divided?
into antigenic groups known as Lancefield groupings
What is the distinction that categorizes Lancefield groupings?
carbohydrate composition of bacterial antigens located in cell wall
How are the Lancefield groupings designated?
by a single letter (A, B, C)
What Lancefield group does streptococcus pyrogens belong to?
Group A
What is important about streptococcus pyogenes?
causative agent behind more than 90% of human strep infections resulting in pharyngitis, scarlet fever, or rheumatic fever
What is streptococcal pharyngitis commonly known as?
strep throat
What Lancefield group does streptococcal pharyngitis belong to?
Group A
What is strep throat characterized by?
enlarged lymph nodes, fever, reddening within the lining of the throat surface
What can strep throat lead to if left untreated?
rheumatic fever
How often does rheumatic fever occur in untreated streptococcal pharyngitis cases?
3%
When does rheumatic fever present?
2-3 weeks post infection
What are common symptoms of rheumatic fever?
inflammation in the joints, involuntary jerking movements; nodules beneath the skin, and reddened areas with raised edges over the surface of the skin
