Updated: 9/30/2018

Escherichia coli

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Introduction
 
  • Classification
    • bacteria
      • gram-negative bacilli
        • the enterics
          • facultative anaerobes
            • lactose fermenting
              • Escherichia
                • E. coli
Pathogenesis
  • Transmission
    • endogenous
    • fecal-oral
    • contaminated food
      • undercooked meat
  • Reservoir
    • normal colonic flora
    • cow feces
  • Molecular biology
    • normal flora acquires virulence factors
      • pili 
        • P-fimbrae virulence factor is most important for colonization of urinary tract 
      • exotoxin
        • LT
        • ST
        • shiga-like
      • endotoxin
        • lipid A part of LPS
      • K capsule  
        • K-1 capsular antigen allows meningeal infection
      • iron-binding siderophore
    • molecular mechanism of virulence depends on strain (see below)
Laboratory
  • Oxidase negative
  • Most E. coli ferment sorbitol
    • except EHEC which usually does not
  • Distinguish pathogenic strains via
    • immunoassay
    • serotyping
    • DNA probes
    • PCR
Clinical Conditions
  • Diarrhea
    • severity of diarrhea depends on strain ("PITcH")
    • virulence factors are shared between VibrioE. coli, and Shigella
      • EPEC ("pediatric")
        • second most common cause of diarrhea in infants
        • adherence to M cells prevents absorption
          • no Shiga toxin produced, but some strains may produce Shiga-like toxin
        • developing countries
      • EIEC ("inflammatory")
        • bacteria invade epithelial cells
          • invasion and toxin act synergistically
        • virulence factor is shared by Shigella
        • blood and WBC in stool
          • like Shigellosis
      • ETEC ("traveler") 
        • LT (heat labile) toxin
          • similar to cholera toxin
          • ↑ cAMP
        • ST (heat stable) toxin
        • secretion of Cl- and HCO3- into intestinal lumen results in rice-water stools resembling those seen in cholera
      • EHEC ("hamburger")
        • Shiga-like toxin (verotoxin)
          • inhibits protein synthesis by inhibiting 60S ribosome 
        • no invasion of epithelium
          • virulence is only toxin-mediated
        • blood in stool
          • but no WBCs because no invasion
        • hemolytic uremic syndrome (HUS)
          • O157:H7 strain associated 
          • classic triad
            • anemia
            • thrombocytopenia
            • acute renal failure
          • swelling of endothelium narrows lumen leading to
            • hemolysis
            • ↓ renal blood flow
            • ↓ platelets as damage is repaired
          • O157:H7 strain does not ferment sorbitol nor does it produce glucuronidase (vs. most other E. coli strains)
      • EAEC 
        • enteroaggregative E. coli
        • has the ability to adhere to intestinal cells
        • cause of traveler's diarrhea to less-developed countries
  • UTI
    • most common cause of UTI
    • acquisition of pili allows motility up the GU tract
    • ascending infection can cause pyelonephritis
  • Neonatal meningitis
    • second most common cause (vs. group B strep)
    • acquisition of K capsule inhibits phagocytosis to allow spread to meninges 
  • Sepsis
    • most common cause of Gram-negative sepsis
    • hospitalized patients
  • Pneumonia
    • hospital acquired
    • in neonates
  • Cystitis
  • Pyelonephritis
Treatment for Common Clinical Conditions Caused by E.Coli
EPEC diarrhea Supportive
EIEC diarrhea -----
ETEC diarrhea Rehydration with TMP/SMX
EHEC diarrhea Supportive (do not use antibiotics - they may cause HUS)
UTI Fluoroquinolones or sulfonamides
Neonatal meningitis Ceftriaxone
Sepsis Fluoroquinolones or 3rd generation cephalosporins

 

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Questions (7)
Lab Values
Blood, Plasma, Serum Reference Range
ALT 8-20 U/L
Amylase, serum 25-125 U/L
AST 8-20 U/L
Bilirubin, serum (adult) Total // Direct 0.1-1.0 mg/dL // 0.0-0.3 mg/dL
Calcium, serum (Ca2+) 8.4-10.2 mg/dL
Cholesterol, serum Rec: < 200 mg/dL
Cortisol, serum 0800 h: 5-23 μg/dL //1600 h:
3-15 μg/dL
2000 h: ≤ 50% of 0800 h
Creatine kinase, serum Male: 25-90 U/L
Female: 10-70 U/L
Creatinine, serum 0.6-1.2 mg/dL
Electrolytes, serum  
Sodium (Na+) 136-145 mEq/L
Chloride (Cl-) 95-105 mEq/L
Potassium (K+) 3.5-5.0 mEq/L
Bicarbonate (HCO3-) 22-28 mEq/L
Magnesium (Mg2+) 1.5-2.0 mEq/L
Estriol, total, serum (in pregnancy)  
24-28 wks // 32-36 wks 30-170 ng/mL // 60-280 ng/mL
28-32 wk // 36-40 wks 40-220 ng/mL // 80-350 ng/mL
Ferritin, serum Male: 15-200 ng/mL
Female: 12-150 ng/mL
Follicle-stimulating hormone, serum/plasma Male: 4-25 mIU/mL
Female: premenopause: 4-30 mIU/mL
midcycle peak: 10-90 mIU/mL
postmenopause: 40-250
pH 7.35-7.45
PCO2 33-45 mmHg
PO2 75-105 mmHg
Glucose, serum Fasting: 70-110 mg/dL
2-h postprandial:<120 mg/dL
Growth hormone - arginine stimulation Fasting: <5 ng/mL
Provocative stimuli: > 7ng/mL
Immunoglobulins, serum  
IgA 76-390 mg/dL
IgE 0-380 IU/mL
IgG 650-1500 mg/dL
IgM 40-345 mg/dL
Iron 50-170 μg/dL
Lactate dehydrogenase, serum 45-90 U/L
Luteinizing hormone, serum/plasma Male: 6-23 mIU/mL
Female: follicular phase: 5-30 mIU/mL
midcycle: 75-150 mIU/mL
postmenopause 30-200 mIU/mL
Osmolality, serum 275-295 mOsmol/kd H2O
Parathyroid hormone, serume, N-terminal 230-630 pg/mL
Phosphatase (alkaline), serum (p-NPP at 30° C) 20-70 U/L
Phosphorus (inorganic), serum 3.0-4.5 mg/dL
Prolactin, serum (hPRL) < 20 ng/mL
Proteins, serum  
Total (recumbent) 6.0-7.8 g/dL
Albumin 3.5-5.5 g/dL
Globulin 2.3-3.5 g/dL
Thyroid-stimulating hormone, serum or plasma .5-5.0 μU/mL
Thyroidal iodine (123I) uptake 8%-30% of administered dose/24h
Thyroxine (T4), serum 5-12 μg/dL
Triglycerides, serum 35-160 mg/dL
Triiodothyronine (T3), serum (RIA) 115-190 ng/dL
Triiodothyronine (T3) resin uptake 25%-35%
Urea nitrogen, serum 7-18 mg/dL
Uric acid, serum 3.0-8.2 mg/dL
Hematologic Reference Range
Bleeding time 2-7 minutes
Erythrocyte count Male: 4.3-5.9 million/mm3
Female: 3.5-5.5 million mm3
Erythrocyte sedimentation rate (Westergren) Male: 0-15 mm/h
Female: 0-20 mm/h
Hematocrit Male: 41%-53%
Female: 36%-46%
Hemoglobin A1c ≤ 6 %
Hemoglobin, blood Male: 13.5-17.5 g/dL
Female: 12.0-16.0 g/dL
Hemoglobin, plasma 1-4 mg/dL
Leukocyte count and differential  
Leukocyte count 4,500-11,000/mm3
Segmented neutrophils 54%-62%
Bands 3%-5%
Eosinophils 1%-3%
Basophils 0%-0.75%
Lymphocytes 25%-33%
Monocytes 3%-7%
Mean corpuscular hemoglobin 25.4-34.6 pg/cell
Mean corpuscular hemoglobin concentration 31%-36% Hb/cell
Mean corpuscular volume 80-100 μm3
Partial thromboplastin time (activated) 25-40 seconds
Platelet count 150,000-400,000/mm3
Prothrombin time 11-15 seconds
Reticulocyte count 0.5%-1.5% of red cells
Thrombin time < 2 seconds deviation from control
Volume  
Plasma Male: 25-43 mL/kg
Female: 28-45 mL/kg
Red cell Male: 20-36 mL/kg
Female: 19-31 mL/kg
Cerebrospinal Fluid Reference Range
Cell count 0-5/mm3
Chloride 118-132 mEq/L
Gamma globulin 3%-12% total proteins
Glucose 40-70 mg/dL
Pressure 70-180 mm H2O
Proteins, total < 40 mg/dL
Sweat Reference Range
Chloride 0-35 mmol/L
Urine  
Calcium 100-300 mg/24 h
Chloride Varies with intake
Creatinine clearance Male: 97-137 mL/min
Female: 88-128 mL/min
Estriol, total (in pregnancy)  
30 wks 6-18 mg/24 h
35 wks 9-28 mg/24 h
40 wks 13-42 mg/24 h
17-Hydroxycorticosteroids Male: 3.0-10.0 mg/24 h
Female: 2.0-8.0 mg/24 h
17-Ketosteroids, total Male: 8-20 mg/24 h
Female: 6-15 mg/24 h
Osmolality 50-1400 mOsmol/kg H2O
Oxalate 8-40 μg/mL
Potassium Varies with diet
Proteins, total < 150 mg/24 h
Sodium Varies with diet
Uric acid Varies with diet
Body Mass Index (BMI) Adult: 19-25 kg/m2
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(M1.MC.75) A 23-year-old woman goes to a walk-in clinic while on the fourth day of her honeymoon. She is very upset saying that her honeymoon is being ruined because she is in severe pain. She states that yesterday she began to experience severe pain with urination and seems to be urinating more frequently than normal. She does admit that she has been having increased sexual intercourse with her new husband while on their honeymoon. The physician diagnoses the patient and prescribes trimethoprim-sulfamethoxazole. Which of the following virulence factors is most likely responsible for this patient's infection? Review Topic

QID: 106731
1

LPS endotoxin

5%

(9/180)

2

K capsule

9%

(16/180)

3

P fimbriae

70%

(126/180)

4

Flagella

8%

(14/180)

5

Exotoxin

7%

(12/180)

M1

Select Answer to see Preferred Response

PREFERRED RESPONSE 3

(M1.MC.13) A 27-year-old male suddenly develops severe abdominal cramping and bloody diarrhea. The patient reports consuming undercooked ground beef four days prior to the onset of the symptoms. Which of the following best describes the toxin-mediated mechanism of this disease process? Review Topic

QID: 101472
1

Depolymerization of actin filaments in gastrointestinal mucosal cells, leading to mucosal cell death

11%

(27/248)

2

Increased pH of gastrointestinal lumen resulting in reduced mucosal absorption

0%

(1/248)

3

Increased intracellular cAMP in gastrointestinal mucosal cells, resulting in decreased absorption and increased secretion in the digestive tract

20%

(49/248)

4

Inhibition of elongation factor-2 (EF-2), resulting in decreased protein synthesis in gastrointestinal mucosal cells

17%

(42/248)

5

Inhibition of the 60S ribosomal subunit, resulting in decreased protein synthesis in gastrointestinal mucosal cells

50%

(124/248)

M1

Select Answer to see Preferred Response

PREFERRED RESPONSE 5
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