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Streptococcus pneumoniae
Chapter 23
Streptococcus pneumoniae
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S. pneumoniae was isolated independently by
Pasteur and Steinberg more than 100 years ago.
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Also called “pneumococcus”
Pneumococcal disease is still a leading cause of
morbidity and mortality.
PHYSIOLOGY AND STRUCTURE
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Gram + coccus
0.5 to 1.2 μm in diameter, oval or lancet
shaped, and arranged in pairs and short
chains (Figure 23-9).
Older cells decolorize readily and appear
gram-negative.
PHYSIOLOGY AND STRUCTURE
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S. pneumoniae has fastidious nutritional
requirements and can grow only on enriched
media supplemented with blood products.
α-hemolytic on blood agar if incubated
aerobically and may be β-hemolytic if grown
anaerobically.
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The α-hemolytic appearance results from production
of an enzyme that degrades hemoglobin,
pneumolysin, which produces a green product.
Figure 23-9 Gram stain of Streptococcus pneumoniae.
PHYSIOLOGY AND STRUCTURE
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S. pneumoniae, like all streptococci, lacks
catalase.
S. pneumoniae grows poorly in media with
high glucose concentrations.
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Fermentation → lactic acid rapidly reaches toxic
levels in such preparations.
PHYSIOLOGY AND STRUCTURE
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Virulent strains of S. pneumoniae are covered
with a complex polysaccharide capsule.
It is these polysaccharides that are used for the
serologic classification of strains; currently, 90
serotypes are recognized.
Purified capsular polysaccharides from the most
commonly isolated serotypes are used in the
pneumococcal vaccine.
Pathogenesis
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Not very well understood
Primary damage and disease come from
our immune response and not toxins, etc.
Virulence factors – Table 23-6
Epidemiology
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5-75% of people are colonized
Most infections are caused by endogenous spread
from the colonized nasopharynx or oropharynx to
distal site (e.g., lungs, sinuses, ears, blood,
meninges)
Person-to-person spread through infectious droplets
is rare
Typically a secondary infection (after the flu, etc.)
Young children and the elderly are at greatest risk
for meningitis
Although the organism is ubiquitous, disease is more
common in cool months
Figure 23-10 - The incidence of carriage &
associated disease is highest during the cool months.
Epidemiology
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Most infections are caused by endogenous spread from the
colonized nasopharynx or oropharynx to distal site (e.g., lungs,
sinuses, ears, blood, meninges)
Person-to-person spread through infectious droplets is rare
Individuals with antecedent viral respiratory tract disease or
other conditions that interfere with bacterial clearance from
respiratory tract are at increased risk for pulmonary disease
Young children and the elderly are at greatest risk for
meningitis
Although the organism is ubiquitous, disease is more common
in cool months
CLINICAL DISEASES
- Pneumonia
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500,000 cases per year
Acute onset, consisting of a severe shaking chill and
sustained fever
Symptoms of a viral respiratory tract infection 1 to 3
days prior.
Cough with blood-tinged sputum
Chest pain (pleurisy).
Lobar pneumonia
Rapid recovery following the initiation of appropriate
antimicrobial therapy, with complete resolution in 2
to 3 weeks.
CLINICAL DISEASES
- Sinusitis and Otitis Media
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Over 7 million cases per year
Acute infections of the paranasal sinuses and middle
ear.
Usually preceded by a viral infection of the upper
respiratory tract,
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polymorphonuclear leukocytes (PMN) infiltrate and obstruct
the sinuses and ear canal.
Middle ear infection (otitis media) is primarily seen
in young children, but bacterial sinusitis can occur
in patients of all ages.
Figure from other text
CLINICAL DISEASES
- Meningitis
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6000 cases per year
Infection of the central nervous system following
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bacteremia
infections of the ear or sinuses
head trauma that causes a communication between the
subarachnoid space and the nasopharynx.
Bacterial meningitis can occur in patients of all ages
but is primarily a pediatric disease.
Mortality and severe neurologic deficits are 4 to 20
times more common in patients with meningitis
caused by S. pneumoniae than in those with
meningitis resulting from other organisms.
CLINICAL DISEASES
- Bacteremia
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55,000 cases per year
Occurs in 25% to 30% of patients with
pneumococcal pneumonia and in more than
80% of patients with meningitis.
In contrast, bacteria are generally not
present in the blood of patients with sinusitis
or otitis media.
Endocarditis can occur in patients with
normal or previously damaged heart valves.
Treatment, Prevention, and Control
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Penicillin is the drug of choice for susceptible strains
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In cases of allergy to penicillin or penicillin-resistnats
other drugs are used;
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Antibiotic resistance is increasingly common
Cephalosporins
Erythromycin
Chloramphenicol
Vancomycin
Immunization is recommended for all children
younger than 2 years of age and for adults at risk for
disease