Streptococcus pneumoniae

 Streptococcus pneumoniae

VIRIDANS Streptococcus

·      Viridans Streptococci are a heterogeneous group of α-hemolytic and non-hemolytic Streptococci.

·  Viridans Streptococci is the normal flora of the Oropharynx, Respiratory tract and Gastrointestinal tract of infants, children and adults.

·      Their group name is derived from viridis (Latin for “green”), a reflection of the fact that many of these bacteria produce a Green pigment on Blood agar media.

·       More than 30 species and sub-species have been identified under Viridans Streptococci.

·       Streptococcus pneumoniae is the most virulent member of the Viridans group.

·  Other Viridans Streptococci can be differentiated from Streptococcus pneumoniae using an Optochin test and Capsule. Other Viridans Streptococci are Optochin resistant and they also lack Capsule.

·       Most strains of Viridans Streptococci were highly susceptible to Penicillin.

GENERAL CHARACTERISTICS

·       Gram’s classification – Gram positive bacteria

·       Shape – Lancet shaped cocci (elongated cocci with a slightly pointed outer curvature)

·       Arrangement – Chain form often having Diplococcal arrangement.

·       Motility – Non-Motile

·       Capsule - Present

·       Endospores - Absent

·       Respiration – Aerobic/Facultative anaerobic

·       Optimum Temperature - 37 °C

·       Optimum pH – 7.8

·       Habitat – Respiratory tract.

·       Also called as Pneumococci. Previously called as Diplococcus pneumoniae.

·       Discovered by Louis Pasteur in 1881.

 PATHOGENICITY OF Streptococcus pneumoniae

DISEASE TRANSMISSION

            Streptococcus pneumoniae infections are mainly transmitted by Person-to-person spread by respiratory droplets.

INCUBATION PERIOD

1 - 3 Days

VIRULENCE FACTORS OF Streptococcus pneumonia

• Capsule
• Pneumococcal protein (Pneumococcal Surface Protein and Pneumolysin)
• Cell wall and Cell wall polysaccharides
• Enzymes (Autolysin, Neuramidase, Peptide permease and IgA Protease)
• Hydrogen peroxide

PATHOGENESIS OF Streptococcus pneumoniae

·       Initially Streptococcus pneumoniae, colonize Oropharynx (surface protein adhesions).

·       Spread into normally sterile tissues (Pneumolysin and IgA protease).

·  Stimulate local Inflammatory response (Teichoic acid, Peptidoglycan fragments and Pneumolysin).

·       Finally prevents Phagocytic killing (Polysaccharide capsule). 

CLINICAL DISEASES CAUSED BY Streptococcus pneumoniae (SUPPURATIVE DISEASES)

(i) Pneumonia

·     Pneumococcal pneumonia develops when the bacteria multiply in the alveolar spaces. After aspiration, the bacteria grow rapidly in the nutrient-rich edema fluid.

·      The onset of the clinical manifestations of pneumococcal pneumonia is abrupt, consisting of a severe shaking chill and sustained fever of 39° C to 41° C.

·    Most patients have a productive cough with blood-tinged sputum, and they commonly have chest pain (pleurisy).

·       The disease is generally localized in the lower lobes of the lungs (Lobar pneumonia). 

 

(ii)  Sinusitis and Otitis media

·     Streptococcus pneumoniae is a common cause of acute infections of the Paranasal sinuses and Ear.

·   Middle ear infection (Otitis media) is primarily seen in young children, but bacterial sinusitis can occur in patients of all ages.

(iii)  Meningitis

·     Streptococcus pneumoniae can spread into the central nervous system after bacteremia, infections of the ear or sinuses.

·     Pneumococcal meningitis is relatively uncommon in neonates, S. pneumoniae is now a leading cause of disease in children and adults.

·  Mortality is 4 to 20 times more common in patients with meningitis caused by Streptococcus pneumoniae than meningitis resulting from other organisms.

(iv)   Bacteremia

·    Bacteremia occurs in 25 % to 30 % of patients with pneumococcal pneumonia and in more than 80 % of patients with meningitis.

·       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. Destruction of valve tissue is common.

LABORATORY DIAGNOSIS OF Streptococcus pneumoniae

MICROSCOPIC EXAMINATION

·     Gram stating – Violet coloured Gram positive lancet shaped cocci arranged in form of chains or Diplococci, surrounded by unstained Capsules.

·     Negative staining – Unstained capsules observed in stained background.

·     Quellung reaction - Also called the Neufeld reaction in which antibodies bind to the bacterial capsule of Streptococcus pneumoniae. The antibody reaction allows these species to be visualized under a microscope. If the reaction is positive, the capsule becomes swollen and appears to enlarge.  

·     Motility test – Non-Motile.

COLONY MORPHOLOGY ON CULTURE MEDIUM

·     Blood agar – Gray colonies with Alpha hemolysis (under aerobic condition) or Beta hemolysis (under anaerobic condition) are observed after overnight incubation.

·     MacConkey agar – Pink coloured Lactose fermenting colonies.

CONFIRMATORY TESTS

• Opthacin sensitive test - Streptococcus pneumoniae is identified by its sensitivity to Optochin.
• Bile solubility test - Streptococcus pneumoniae are lysed rapidly when the Autolysins are activated after exposure to Bile.
• Inulin fermentation test - Streptococcus pneumoniae ferments Inulin (Polysaccharide) and hence differentiate it from other Streptococci.
• Antigen detection (CRP Test) - Latex agglutination test using the latex particles coated with anti-CRP antibody is employed to detect C reactive protein.
• Antibody detection – Indirect Hemagglutination Test, Indirect Fluorescence test & ELISA.
• Molecular diagnosis – PCR and Nucleic acid probes analysis.

ANTIBIOTIC THERAPY AND PREVENTION

• Most Pneumococci are susceptible to Penicillin. Penicillin-resistant Pneumococci are being increasingly documented.
• Macrolides or selected Fluoroquinolones with activity against Pneumococci, are available for patients who are allergic to Penicillin.
• Most Penicillin resistant strains remain sensitive to Third generation Cephalosporins (such as Cefotaxime or Ceftriaxone), and all are still sensitive to Vancomycin.
• For serious pneumococcal infections, treatment with a combination of antibiotics is recommended. Vancomycin combined with Ceftriaxone is used commonly for treatment, followed by Monotherapy with an effective Cephalosporin, Fluoroquinolones or Vancomycin.
• Ceftriaxone can be used for treating Meningitis.
• Amoxicillin is the drug of choice for treatment of Otitis media, Sinusitis and Pneumonia.
• Vancomycin is used if the Pneumococci is resistant to Ceftriaxone.
• Pneumococcal vaccines: 23 valent pneumococcal polysaccharide vaccine (PPSV23) and polyvalent pneumococcal conjugate vaccine (PCV13) play an important role in prevention of Pneumococcal diseases.