Transcript Welcome to Ms. Looney`s Biology Class

Streptococcus
Medical Microbiology
Spring 2010
Streptococcus
• Gram-positive cocci
• Most are facultative anaerobes
• How can streptococci be told apart from
staphylococci?
– Streptococci are catalase negative
• Differentiation of species within this genus
is a little more complicated.
• Must use a combination of serotype and
hemolysis
– Serotype: look at the type of surface antigens
– Hemolysis patterns: look at how the bacteria
hemolyse red blood cells (grow on blood
agar)
– Other biochemical tests
•Alpha hemolysis is shown by a greenish halo around the colony (a.k.a.
incomplete hemolysis).
•Beta hemolysis is shown by a clear halo around the colony and is
produced by complete hemolysis of the red blood cells (a.k.a. complete
hemolysis).
•Gamma hemolysis is shown as no hemolysis or discoloration of the
blood.
Streptococcus pyogenes
• Most notorious of the Streptococci
• Causes a variety of suppurative and nonsuppurative disease
– Phyaryngitis all the way to life-threatening
diseases like the “flesh eating” bacteria
S. pyogenes
• Grow best on blood agar
– After 24 hour incubation, colonies are 1-2 mm
and white with large zones of B-hemolysis
(complete hemolysis)
Type Proteins
• M protein (antigen)- associated with
virulent streptococci
• T protein- epidemiologic marker of
unknown significance
S. pyogenes
• Some produce a capsule that is
antigenically indistinguishable from
hyaluronic acid to mammalian tissue
– Tricks mammals’ bodies into thinking it
belongs, preventing phagocytosis
Virulence factors for S. pyogenes
• Capsule, lipoteichoic acid, M protein, Mlike protein, and F protein (all help the
bacteria adhere to stuff)
• Pyrogenic exotoxin
– Fever, rashes
• Streptolysin S, Streptolysin O, and
Streptokinase
– Lyse cells
S. pyogenes virulence cont.
• DNase: makes pus more runny
• C5a peptidase: causes further
inflammation
Epidemiology
• In 2004 in the U.S.
– 500 cases Streptococcal TSS (45%fatal)
– 500 cases necrotizing fasciitis (25%fatal)
– 10 million cases of non-invasive disease
– Let’s start with the fun diseases
first….suppuratives woot!
Pharyngitis
• Streptococcal pharyngitis = strep throat
Scarlet fever
• Complication of pharyngitis (caused when exotoxin is released after
bacterial cells are lysed by bacteriophage)
• 1-2 days after pharyngitis; red rash appears; strawberry tongue
Pyoderma (impetigo)
Erysipelas (upper skin layers)
• Red, warm, lymph node enlargement,
systemic signs
Cellulitis (deeper skin
layers/subcutaneous tissue)
• Similar to erysipelas
Necrotizing fasciitis
Rheumatic fever
• Non-suppurative complication of S.
pyogenes infection
• Characterized by swelling of heart, joints,
blood vessels
Acute glomerulonephritis
• Inflammation of the glomeruli
• Hypertension, hematuria, proteinuria
Streptococcus pyogenes
• Not typically found on the skin, but
commonly found in the mouth
• Gram stains used to make a quick,
preliminary diagnosis
Treatment for S. pyogenes
infections
• Penicillin works pretty well still
• Erythromycin or cephalosporin if patient is
allergic to penicillin
• Patients with a history of rheumatic fever
may require antibiotic prophylaxis
Streptococcus Agalactiae
• Indistinguishable from S. pyogenes from
Gram stain
• On blood agar, they have narrow zones of
B-hemolysis (what was S. pyogenes??)
• Different antigens than S. pyogenes
Streptococcus agalactiae
• Very young are at the greatest risk for
these infections (major cause of
septicemia and meningitis in newborns)
– Less than 7 days old = early-onset disease
– Disease appears when baby is 1-3 weeks old
= late-onset disease
Early-onset neonatal disease
• Acquired in utero or at birth
• bacteremia, pneumonia, meningitis
– If meningitis and if they survive, they have a
greater chance for blindness, deafness, and
mental retardation
Late-Onset Neonatal disease
• Acquired from exogenous source
• Bacteremia, meningitis
– If meningitis, neurologic complications are
common
Streptococcus pneumoniae
• Isolated by Pasteur more than 100 yrs ago
• Encapsulated
• May appear gram neg. because they
decolorize rapidly
S. pneumoniae
• Normally colonizes the oropharynx and
nasopharynx but can spread to lungs
(pneumonia) or sinuses (sinusitis), or ears
(otitis media), or meninges (meningitis)
1. Grab a book. Copy and fill in the following
table in your notes:
S. pneumoniae Characteristics:
infection:
Pneumonia
Sinusitis
Otitis media
Meningitis
Treatment:
2. Complete the case study at the end of Ch.
23. You will turn this part in so do it on
another sheet of paper.
S. pneumoniae