Microbiology
Pathogens
Regarding Escherichia coli, which of the following statements is INCORRECT:
Answer:
Escherichia coli is a Gram-negative bacilli that is an important member of the intestinal flora. It is the most common cause of UTI in adults, and an important cause of neonatal meningitis. E. coli O157 strain is implicated in the development of dysentery associated with haemolytic uraemic syndrome characterised by haemolytic anaemia, thrombocytopenia and acute renal failure.Escherichia Coli
Microbiology / Pathogens / Klebsiella and Enterobacteriae
Last Updated: 6th December 2020
| Microorganism | Escherichia coli |
|---|---|
| Gram stain | Gram negative |
| Shape | Rod |
| Oxygen requirements | Facultative anaerobe |
| Oxidase | Negative |
| Additional features | Lactose-fermenting, produces exotoxin |
| Reservoir | Intestinal flora, contaminated food and water |
| Transmission | Faecal-oral, peripartum |
| Diseases | UTI, diarrhoea, peritonitis, wound infections, abdominal sepsis, neonatal meningitis N.B. E.coli O157 is associated with HUS and TTP |
Transmission
Escherichia coli is a facultatively anaerobic, Gram-negative bacilli that forms a consistent component of the normal intestinal flora. Transmission is via the faecal-oral route or via local spread of flora (eg. UTI).
Pathogenesis
Strains of E. coli possess a range of different pathogenic mechanisms (including pili, a capsule, endotoxin and exotoxins) that enable them to cause a diverse range of infectious diseases.
Certain uropathic strains are characterised by pili with adhesion proteins that bind to specific receptors on the urinary tract epithelium. The motility of E. coli aids its ability to ascend the urethra into the bladder or ascend the ureter into the kidney.
Clinical Disease
It is the most common cause of uncomplicated urinary tract infection in adults (about 70 - 95% of cases), primarily occurring as an endogenous infection. It is also the most common cause of nosocomial urinary tract infections, associated with the use of indwelling urinary catheters.
E. coli is an important pathogen in neonatal meningitis and septicaemia associated with a high mortality. Exposure of the newborn to E. coli occurs during birth as a result of colonisation of the vaginal canal. It may also cause meningitis or brain abscess following neurosurgical procedures, especially when prosthetic devices are inserted. Enterobacteriaceae are often found as part of the polymicrobial flora of brain abscess.
Some strains of E. coli, acquired through ingestion of contaminated food and water, may cause a exotoxin-mediated watery diarrhoea (very common cause of traveller's diarrhoea), an enteroinvasive shigellosis-like disease or a haemorrhagic dysentery. Antibiotic therapy is not usually indicated in diarrhoeal diseases.
E. coli serotype O157 (mainly found in undercooked beef) causes a bloody diarrhoea associated with haemolytic uraemic syndrome (particularly in children), characterised by haemolytic anaemia, thrombocytopenia and acute renal failure.
E.coli may also be implicated in peritonitis, pneumonia (hospital acquired and neonatal), wound infection and septicaemia.
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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 |
