Disease caused by Streptococcus pneumoniae
The Streptococcus pneumoniae is gram-positive lancet shape bacteria. It may be diplococcus or streptococcus. Pneumococcus is non-motile, non-spore forming capsulated bacteria. They may be aerobic or facultative anaerobic in nature. They are a normal inhabitant of human respiratory tract Pneumococcus bacteria may be an important cause of pneumonia, otitis, sinusitis, bronchitis, meningitis and other infection like arthritis, conjunctivitis and suppurative lesions.
1. Morphology
- Pneumococci are lancet shape with one end broad or rounded and other end pointed
- If they occur in pair called as diplococci.
- They are smaller than 1 micrometre in size.
- The capsule enclose each pair of cells. These capsules can be made visible by using capsule staining method.
- These cells are readily stained by gram staining procedure.
2. Cultural characters
- Pneumococci require enriched culture for its growth.
- They may require anaerobic or facultative anaerobic condition for growth.
- The optimum temperature for its growth is 37° C and can grow in the temperature range of 25° C to 42° C.
- The optimum pH -7.8 and can grow at a pH range of 6.5 to 8.3.
- Dome shape colonies with an area of green decolourisation occur after incubation on blood agar and on further incubation colonies become flat.
- Pneumococcus colonies on blood agar under anaerobic condition show zone of beta haemolysis.
- In glucose broth, uniform turbidity is observed.
- The cocci undergo autolysis by intracellular enzymes.
3. Biochemical reaction
- Pneumococci ferment inulin and this fermentation differentiates Pneumococcus from other Streptococci.
- It also ferments many sugars result in the production of acid and no gas.
- Pneumococci solubilize bile constantly so it is important for diagnosis.
- It shows catalase and oxidase test negative.
4. Resistance
- Pneumococci are heat sensitive organism its thermal death point is 52 °C for15 minutes.
- It is sensitive to antibiotics.
- Prolonged incubation kills bacterial cells due to the production of toxic peroxides.
- These strains are sensitive to many antibiotics like penicillin.
5. Toxins and other virulence factors
- The virulence depends on capsule and toxin production called as pneumolysin.
- The capsular polysaccharide of Pneumococci is acidic and hydrophilic in nature so these cells are protected from phagocytosis.
- Pneumococci produce pneumolysin it is the membrane-damaging toxin and shows cytotoxicity and complement activating protein.
6. Pathogenicity
- Intraperitoneal inoculation in mice and rabbit can cause a fatal infection.
- Pneumococcus can localise in the human nasopharynx and can infect middle ear and respiratory tract.
- Generally, infection is endogenous but highly virulent strains can also cause exogenous infections.
- Pneumococci are a cause of pneumonia and bronchopneumonia.
7. Epidemiology
- The transmission of infection takes place by inhalation of droplets contaminated with Pneumococci.
- The carrier is the respiratory tract of patient or droplet nuclei.
- Disease result when the immunity of a person is low and the person gets infected with Pneumococci.
8. Laboratory diagnosis
- The sputum sample is collected from the patient.
- The sputum sample is homogenized and gram staining procedure is carried out.
- After homogenization, it is inoculated on blood for 37 °C for 24 hours.
- In case of infants serum coated laryngeal swaps are used.
- Gram-stained CSF is used for presumptive diagnosis and gram-positive diplococci are observed.
9 . Treatment
- Antibiotic used for the treatment are penicillin and amoxicillin.
- If the strains are resistant to other antibiotics like erythromycin and tetracycline are used.
- In serious infections, vancomycin and cephalosporin drugs are of choice.