Microbiology
Pathogens
Regarding Streptococcus pneumoniae, which of the following statements is CORRECT:
Answer:
Streptococcus pneumoniae is an encapsulated diplococci normally present in nasopharyngeal flora. Transmission can occur via the respiratory droplet route but infection is usually endogenous. It is a rare cause of infective endocarditis and a common cause of bacterial meningitis.Streptococcus Pneumoniae
Microbiology / Pathogens / Streptococci and Staphylococci
Last Updated: 21st April 2019
| Microorganism | Streptococcus Pneumoniae |
|---|---|
| Gram stain | Gram positive |
| Shape | Cocci (diplococci) |
| Catalase | Negative |
| Oxygen requirements | Facultative anaerobe |
| Haemolysis | Alpha-haemolytic |
| Additional features | Encapsulated |
| Reservoir | Nasopharynx |
| Common diseases | Pneumonia, meningitis, sinusitis, otitis media, cellulitis, deep abscesses |
Transmission
Streptococcus pneumoniae is an encapsulated diplococci. It is often found in the normal respiratory flora, particularly in children, smokers and in crowding. Person-to-person spread may occur via the respiratory droplet route although infection is usually endogenous.
Risk Factors
Risk factors for infection include:
- disturbed consciousness predisposing to aspiration e.g. in general anaesthesia, alcoholism, convulsions
- preceding respiratory viral infections e.g. common cold, influenza
- chronic respiratory disease or malignancy
- comorbidities e.g. valvular and ischaemic heart disease
- diabetes mellitus
- chronic renal failure
- immune deficiencies e.g. asplenia/hyposplenia, hypogammaglobulinaemia, HIV, complement deficiency
Clinical Disease
It primarily causes disease of the airways (pneumonia, empyema, COPD exacerbation) and associated tissues (otitis media, sinusitis, mastoiditis). It is the most common cause of community acquired pneumonia.
Direct or haematogenous spread can give rise to meningitis; it is one of the most common causes of acute bacterial meningitis in children and adults in the UK.
Less commonly it can cause cellulitis, abscesses, peritonitis and endocarditis.
Treatment
Penicillins, macrolides or tetracyclines are usually the treatment of choice for respiratory infections, but third generation cephalosporins (e.g. cefotaxime) are often used for meningitis and where high-level penicillin or cephalosporin resistance occurs, a glycopeptide (e.g. vancomycin) should be added.
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- Biochemistry
- Blood Gases
- Haematology
| Biochemistry | Normal Value |
|---|---|
| Sodium | 135 – 145 mmol/l |
| Potassium | 3.0 – 4.5 mmol/l |
| Urea | 2.5 – 7.5 mmol/l |
| Glucose | 3.5 – 5.0 mmol/l |
| Creatinine | 35 – 135 μmol/l |
| Alanine Aminotransferase (ALT) | 5 – 35 U/l |
| Gamma-glutamyl Transferase (GGT) | < 65 U/l |
| Alkaline Phosphatase (ALP) | 30 – 135 U/l |
| Aspartate Aminotransferase (AST) | < 40 U/l |
| Total Protein | 60 – 80 g/l |
| Albumin | 35 – 50 g/l |
| Globulin | 2.4 – 3.5 g/dl |
| Amylase | < 70 U/l |
| Total Bilirubin | 3 – 17 μmol/l |
| Calcium | 2.1 – 2.5 mmol/l |
| Chloride | 95 – 105 mmol/l |
| Phosphate | 0.8 – 1.4 mmol/l |
| Haematology | Normal Value |
|---|---|
| Haemoglobin | 11.5 – 16.6 g/dl |
| White Blood Cells | 4.0 – 11.0 x 109/l |
| Platelets | 150 – 450 x 109/l |
| MCV | 80 – 96 fl |
| MCHC | 32 – 36 g/dl |
| Neutrophils | 2.0 – 7.5 x 109/l |
| Lymphocytes | 1.5 – 4.0 x 109/l |
| Monocytes | 0.3 – 1.0 x 109/l |
| Eosinophils | 0.1 – 0.5 x 109/l |
| Basophils | < 0.2 x 109/l |
| Reticulocytes | < 2% |
| Haematocrit | 0.35 – 0.49 |
| Red Cell Distribution Width | 11 – 15% |
| Blood Gases | Normal Value |
|---|---|
| pH | 7.35 – 7.45 |
| pO2 | 11 – 14 kPa |
| pCO2 | 4.5 – 6.0 kPa |
| Base Excess | -2 – +2 mmol/l |
| Bicarbonate | 24 – 30 mmol/l |
| Lactate | < 2 mmol/l |
