Microbiology
Pathogens
A 28 year old man, who underwent a splenectomy 1 year ago following trauma, presents to ED having collapsed. On examination he is febrile and shocked. You treat him according to sepsis guidelines. He admits to being poorly compliant with medication and has not attended follow-up appointments. Which of the following pathogens is most likely responsible for his symptoms:
Answer:
The patient most likely has pneumococcal sepsis. Patients who have undergone splenectomy are at risk of certain infections, particularly those caused by Streptococcus pneumoniae, due to a decreased ability to produce IgM antibodies. Patients are usually immunised against this pathogen and take low-dose prophylactic penicillin V to prevent infection.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.
Report A Problem
Is there something wrong with this question? Let us know and we’ll fix it as soon as possible.
Loading Form...
- 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 |
