Streptococcus pneumoniae

What tests are useful for diagnosis?

-*Optochin sensitivity* (differentiates s. pneumoniae from other alpha-hemolytic strep species) -Bile solubility test (bile sensitive) -*Quellung reaction* (capsular precipitation test)- halos around the bacteria cause by swollen capsules. This can determine serotype based on capsular antigens. -Direct fluorescent antibody (DFA) -Rapid latex agglutination -Gram stain -Blood agar cultivation -Antibiogram to determine resistance

What are the s. pneumoniae's virulence factors?

1) Capsule that inhibits phagocytosis (remember that unencapsulated pneumococcus is not virulent) 2) Pneumolysin- a membrane-active exotoxin that causes transmembrane pores which result in cell lysis

What are the steps of pneumococcal pneumonia?

1) Invasion through the bronchial tree 2) Excessive edema in alveoli 3) Bacterial spread peripherally via bronchioles 4) Red hepatization 5) Grey hepatization *Adult pneumococcal pneumonia usually involves one or more complete lobes. In young children and the aged, the infection is usually more patchy.

What is red hepatization?

A state of respiratory infection due to fibrin accumulation and RBC infiltration of the alveolar air spaces. Named hepatization because it makes the lung "solid" like liver, as opposed to it's normal spongy state.

What is grey hepatization?

A state of respiratory infection due to neutrophil infiltration (bacteria are phagocytosed), red cell lysis in the alveolar air spaces. Named hepatization because it makes the lung "solid" like liver, as opposed to it's normal spongy state.

What is the physiology of pneumococcus?

Alpha-hemolytic (pneumolysin). *Optochin sensitive. Most other alpha-hemolytic streptococcus are optochin-resistant*. Sensitive to bile.

What typically precedes an episode of pneumococcal meningitis?

Bacteremia, infection of the ear, sinusitis, or head trauma.

What are the serotypes of pneumococcus based on?

Capsular antigens (K antigens)

What are the clinical manifestations of pneumococcal pneumonia?

Chills and fever (102-106F), sever pleuritic pain, productive cough, rusty sputum. Onset and recovery are abrupt. A crisis may occur 5-10 days after onset.

What is the morphology of s. pneumoniae?

G+ lancet-shaped coccus, usually in pairs or short chains. Looks like ants on a gram stain. Does not possess Lancefield group antigens. Smooth types have a capsule and rough types do not.

When do pneumococcal infections occur the most?

In cooler months when individuals are more likely to stay in close contact and in close quarters. Transmission is directly proportional to frequency and intimacy of contact.

For which age group is pneumococcal pneumonia not an important cause of bacterial meningitis?

Infants. However, in infants and children, pneumococcus is one of the leading causes of otitis media, sinusitis, pneumonia and bacteremia.

Which lobes are usually affected in pneumococcal pneumonia?

Lower lobes (lobar pneumonia), because the disease is associated with aspiration.

Where does s. pneumoniae invade?

Lower respiratory tract

What is the most common clinical manifestation of s. pneumoniae in children?

Ototis media. Infection is usually preceded by a viral infection of the upper respiratory tract.

Pneumovax

Pneumococcal capsular polysaccharide vaccine that includes 23 serotypes responsible for 87% of pneumococcal disease in the US. Primarily recommended for high-risk groups (cardio disease, lung disease, elderly in closed populations)

What is an outward sign that helps differentiate between meningococcal and pneumococcal meningitis?

Pneumococcal meningitis does not cause petechiae like meningococcal meningitis can.

What is a common name for s. pneumoniae?

Pneumococcus

Prevnar

Polysaccharides + modified pneumolysin vaccine that includes 13 most common serotypes responsible for otitis media. 4 dose schedule for infants (2, 4, 6, 12-15 months). This is also being used in older individuals as well.

Which population has the highest carriage rate of s. pneumoniae?

Preschool aged children. This is one of the reasons many hospitals have age restrictions for visitation.

What conditions predispose an individual to s. pneumoniae infections?

Respiratory viral infection, cardiac failure, pulmonary stasis from prolonged bedrest. Factors which slow epiglottal reflex such as chilling and anesthesia can cause aspiration of bacteria from upper respiratory tract. Rarely a primary infection. Usually occurs in compromised respiratory tracts.

What is the most frequent cause of community-acquired meningitis?

S. pneumoniae

Which type of s. pneumoniae is virulent: smooth or rough?

Smooth. However, rough can be converted to smooth via transformation.

What type of samples are used for diagnosis?

Sputum and CSF

Does s. pneumoniae exhibit antibiotic resistance?

Yes. Up to 33% of strains are resistant to penicillin.