Download Strep

NEPAL-2001
STREPTOCOCCUS
• Gram-positive, catalase-negative cocci, part of
normal flora in man and animals. A few species
cause significant morbidity in man.
• Facultative anaerobes.
• The "oral streptococci", including the cariogenic
Streptococcus mutans, are important members
of this group.
Gram stain of
Streptococcus
pyogenes
STREPTOCOCCUS - CLASSIFICATION
• Clinical presentation (pyogenic, oral, enteric)
• Serological properties (Lancefield groups A-H, K-V).
• Hemolytic pattern:
• ß - wide, clear, translucent zone of complete
hemolysis around the colony
• a - partial and green (viridans) discoloration
• g - no hemolysis.
• Biochemical properties
STREPTOCOCCUS
• Group A Streptococcus (S. pyogenes) (ß-hemolysis)
• Group B Streptococcus (GBS) (S. agalacatiae) (ß-hemolysis)
• Viridans Streptococci (a -hemolysis)
(S. mutans, S. sanguis, S. salivarius, S. mitis, S. anginosus )
• Streptococcus pneumoniae (a-hemolysis)
• Enterococcus faecium
Group A Streptococcus (S. pyogenes)
(ß-hemolysis) (pyo - connected with pus)
Suppurative diseases:
Pharyngitis - "strep throat"
Scarlet fever - a complication of streptococcal pharyngitis
Pyoderma (impetigo) - skin infections
Erysipelas - acute infection of the skin
Flesh-eating disease (invasive fascitis)
Streptococcal toxic syndrome (pyrogenic exotoxins)
Non-suppurative diseases:
Acute rheumatic fever, acute glomerulonephritis
Group B Streptococcus (GBS)
Streptococcus agalactiae
(ß-hemolysis)
Septicemia, pneumonia and meningitis
in newborn children (neonatal diseases).
The major cause of neonatal sepsis in
developed countries.
Viridans Streptococci
(a-hemolysis)
(S. mutans, S. sanguis, S. salivarius, S. mitis, S. anginosus )
Dental caries
Subacute endocarditis
Suppurative intraabdominal infections
Streptococcus pneumoniae
(a -hemolysis)
Pneumonia
Sinusitis and otitis media
Meningitis
Septicemia (bacteremia)
Group A Streptococcus (S. pyogenes)
Virulence Factors
• Capsule - composed of hyaluronic acid identical to that
found in connective tissue (non-immunogenic);
antiphagocytic.
• M protein - the most important virulence factor,
located on the end of the hairlike fimbriae, a major
antiphagocytic component.
• M-like proteins bind the Fc portion of IgG and IgM.
• F protein - fibronectin-binding protein (the major
adhesin for bacterial attachment to the epithelial
cells of the pharynx and the skin).
Group A Streptococcus (S. pyogenes)
Virulence Factors (cont.)
• Pyrogenic exotoxins - erythrogenic toxins produced by lysogenic strains of streptococci
(mediate pyrogenecity [fever], superantigens,
responsible for red rash observed in scarlet fever).
• Streptolysin S - non-immunogenic cell-bound
hemolysin (lyses erythrocytes, leukocytes,
platelets; kills phagocytes by autolysis).
• Streptolysin O - immunogenic, kills leukocytes by
autolysis, used for the ASO test (a recent infection).
Group A Streptococcus (S. pyogenes)
Virulence Factors (cont.)
• Streptokinase (fibrinolysin) - lysing blood clots (fibrin).
• DNase - depolymerizes DNA present in pus, reduces the
viscosity of pus, facilitates spread of the organisms.
• Hyaluronidase ("spreading factor") - degrades
connective tissue.
Group A Streptococcus (S. pyogenes) - Epidemiology
A commensal in the naso/oropharynx of healthy
children and young adults, continuous turnover
until antibodies to M protein are produced.
Spread by airborne droplets and by contact.
Disease is caused by recently required strains
capable establish an infection before specific
antibodies are produced or competitive organisms
are able to proliferate.
Group A Streptococcus (S. pyogenes)
(ß-hemolysis) (pyo - connected with pus)
Suppurative diseases:


Pharyngitis - "strep throat"
Scarlet fever - a complication of streptococcal
pharyngitis

Pyoderma (impetigo) - skin infections

Erysipelas - acute infection of the skin

Flesh-eating disease (invasive fascitis)

Streptococcal toxic syndrome (pyrogenic exotoxins)
Non-suppurative diseases:
Acute rheumatic fever, acute glomerulonephritis
Acute stage of
erysipelas of the leg,
acute infection of
the skin with
Streptococcus
pyogenes
Group A Streptococcus (S. pyogenes)
Treatment
• Very sensitive to penicillin (erythromycin for penicillin
sensitive patients).
• Patients with a history of rheumatic fever - long-term use
of antibiotic prophylaxis to prevent recurrent disease.
• Antibiotic prophylaxis before the use procedures that
induce transient bacteremia (e.g., dental procedure).
Group B Streptococcus (S. agalacatiae)
Normal flora of
the female genital
tract in 25-40% of healthy
women.
A significant cause
of septicemia, pneumonia
and meningitis in newborn
children (neonatal diseases).
In ~80% of cases, neonatal infection is acquired during
delivery (direct transmission).
Group B Streptococcus
(S. agalacatiae)
Pathogenesis and Immunity
• No toxins or virulence factors identified
• Antibody developed against the type specific capsular
antigens in group B streptococci are protective
• Infects neonates lacking antibody (maternal antibodies)
Group B Streptococcus (S. agalacatiae)
Epidemiology
Colonize the lower gastrointestinal tract (GIT)
and the genitourinary tract (transient carriage in
10-30% of pregnant women).
Infection can occur:
• In utero
• At the time of birth (80%)
• During the first few months of life
Group B Streptococcus (S. agalacatiae)
Clinical Syndromes
• Early-onset neonatal disease (the first 7 days of life):
bacteremia, pneumonia, meningitis;
60% of low birth weight, premature infants will die and
survivors will have neurological complications
(blindness, deafness, severe mental retardation).
• Late-onset neonatal disease - from an exogenous
source (bacteremia with meningitis, 80% will survive but
neurological complications are common).
• Infection in pregnant women - urinary tract infections.
Group B Streptococcus (S. agalacatiae)
Treatment
Penicillin G is the drug of choice, but the minimum
inhibitory concentration (MIC) is approx. 10 X greater
than with group A streptococci (S. pyogenes).
Tolerance to penicillin - penicillin + aminoglycoside.
Resistance to erthromycin and tetracycline has been
observed.
In the U.S. S. agalacatiae causes ~2500 cases of
infection and 100 deaths per year among newborns.
Viridans Streptococci
(S. mutans, S. sanguis, S. salivarius, S. mitis, S. anginosus )
Heterogeneous group of a- and non-hemolytic - isolated from
the oropharynx
the gastrointestinal tract (GIT)
the urogenital tract
Associated with dental caries, subacute endocarditis (60%),
and suppurative intraabdominal infections
Vertically transmitted from mother to child
Streptococcus pneumoniae
(pneumococcus)
An encapsulated Gram-positive cocci,
oval or lancet-shaped, arranged in pairs
(diplococci) or short chains
a-hemolytic colonies
Gram stain of
Streptococcus
pneumoniae
Streptococcus pneumoniae
Pathogenesis and Immunity
• Capsule - needed for virulence, inhibits
phagocytosis in the absence of specific antibodies;
non-encapsulated [rough] strains are avirulent
•
•
•
•
•
Protein adhesin
Secretory IgA protease
Pneumolysin
Teichoic acid
Hydrogen peroxide
Streptococcus pneumoniae
Epidemiology
• S. pneumoniae - a commensal in the throat and
nasopharynx of healthy individuals (5 to 75%).
• Transmission via respiratory droplets.
• Spread from the nasopharynx and oropharynx to distal
loci: lungs (pneumonia), paranasal sinuses (sinusitis),
ears (otitis media), and meninges (meningitis).
S. pneumoniae - Clinical syndromes
1. Pneumonia - aspiration of the endogenous oral organism
(lobar pneumonia).
2. Sinusitis and otitis media - usually preceded by a viral
infection of the upper respiratory tract.
Otitis usually in children.
3. Meningitis - spread into CNS, primarily a pediatric disease
but can occur at all ages. About 15% of meningitis in
children and 30-50% of adult disease is caused by S.
pneumoniae.
4. Septicemia (bacteremia) - 25-30% of patients with
pneumococcal pneumonia and > 80% of patients with
meningitis.
S. pneumoniae
the most common bacterial cause
of
Pneumonia
Meningitis
Children’s ear infections
S. pneumoniae - Treatment
• Penicillin is the drug of choice.
• Penicillin resistant strains developed in 1977 and now 1/3
of all cases in the U.S. are penicillin resistant (a decreased
affinity of penicillin for the penicillin-binding proteins
present in bacterial wall).
• Vaccine available (covers most pathogens and is long
lasting) but still does not cover those especially at risk
pneumococcal disease (e.g., renal transplants, young
children, and the elderly).
Pneumococcal conjugate vaccine (PCV7)
Approved for infants and toddlers.
Protection for at least 3 years so children vaccinated
as infants will be protected when they are at greatest risk
for serious disease.
Who should get the vaccine and when?
Children under 2 years of age
The routine schedule for pneumococcal conjugate vaccine
is 4 doses, one dose at each of these ages:
~ 2 months
~ 6 months
~ 4 months
~ 12 months
(See lecture notes!)
Gram stain of
Enterococcus
faecalis
ENTEROCOCCUS
• Members of the GI tract - one of the most feared
nosocomial pathogens !!!!!!!!
• Many strains are completely resistant to ALL conventional
antibiotics
• VREF - vancomycin-resistant Enterococcus faecium
emerged in 1989
• By 1997 according to CDC, 50% of all E. faecium were VREF
• Zyvox (linezolid) and Synercid - approved for the treatment
of VREF bacteremia
High Sierra - Sabrina Lake