Gram Negative Enteric Bacilli: E.Coli

Gram Negative Enteric Bacilli : E.Coli

Escherichia Coli Infections

Intestinal Pathogenic Strains

cause diarrheal diseases

Shiga Toxin–Producing And Enterohemorrhagic E. Coli

(1) Shiga toxin–producing E. coli (STEC)/Enterohemorrhagic E. coli (EHEC),

(2) Enterotoxigenic E. coli (ETEC),

(3) Enteropathogenic E. coli (EPEC),

(4) Enteroinvasive E. coli (EIEC),

(5) Enteroaggregative E. coli (EAEC).

• Transmission via contaminated food and water

Gastric acid - protective against infection;

• decreased Acidity increases risk

STEC/EHEC - infection of developed countries

consumption of fresh lettuce, spinach, undercooked ground beef (hamburgers)

O157:H7 - the most prominent serotype - causes Hemorrhagic colitis and the hemolytic-uremic syndrome (HUS).

Shiga -like toxin: active A subunit and binding B subunits

• A subunit irreversibly inhibits ribosomes, induces apoptosis of the cell
• O157:H7 E.Coli- 4th most common cause of bacterial diarrhea (1. Campylobacter, 2. Salmonella 3. Shigella).
• Incubation period of 3 or 4 days.
• Colonic edema and an initial non-bloody diarrhea

Hallmark: grossly bloody diarrhea in >90% of cases.

• Abdominal pain and fecal leukocytes (70% of cases)
• Fever - not common (helpful clue to differentiate from Shigella)
• Self-limited, lasting 5–10 days.

feared complication is Hemolytic-Uremic Syndrome - occurs in 2–8% of cases

• >50% of all cases of HUS are caused by STEC/EHEC.
• fever, thrombocytopenia, RBC hemolysis, renal failure, and encephalopathy.
• mortality rate with dialysis is <10%,

Hemolytic-uremic syndrome(HUS)

E. coli O157:H7, Shigella, and Campylobacter.

1. Endothelial damage

2. platelet and leukocyte activation

3. multiple thromboses in the small blood vessels - damages organs

• gram-negative,
• facultatively anaerobic,
• rod-shaped
• Part of the normal flora of the gut
• produces vitamin K in hosts
• Prevents colonization with other pathogens
• Fecal transmission

1. Hemolytic anemia

2. Acute kidney failure (uremia)

3. Low platelets (thrombocytopenia)

Abdominal and Pelvic Infection

• The abdomen/pelvis is the second most common site of E. coli infection

Acute peritonitis - secondary to fecal contamination

• Spontaneous bacterial peritonitis, dialysis-associated peritonitis, diverticulitis, appendicitis, intraperitoneal or visceral abscesses, infected pancreatic pseudocysts, septic cholangitis and/or cholecystitis.

• In intra-abdominal infections, E. coli is isolated either alone or, more commonly in combination with other facultative and/or anaerobic members of the intestinal flora

Enteropathogenic E. Coli

Pneumonia

Urinary Tract Infection

Structure and Function

• E. coli is not an usual cause of CAP pneumonia

Enteric GNB account for only 2–5% of cases of community-acquired pneumonia (CAP),

Gram Negative Bacilli (GNB) - the most common cause (60–70%) of Hospital-acquired pneumonia - postoperative and ICU patients (ventilator-associated pneumonia).

• Pneumonia due to enteric GNB is a serious disease:
• Attributable mortality rate - 10–20%

• Extracytoplasmic outer membrane - characteristic to gram-negative bacteria.
• Consists of a lipid bilayer with proteins, lipoproteins, and lipopolysaccharide (LPS)

Epidemiology

most frequently by ExPEC - Extraintestinal Pathogenic E. Coli

• Very common infection

Causes Uncomplicated cystitis, pyelonephritis, and catheter-associated UTIs:

• E. coli is the most common pathogen for all UTI syndromes

Causes 85–95% of uncomplicated cystitis:

• Dysuria, urinary frequency, and suprapubic pain.
• Fever and back pain - suspect progression to pyelonephritis
• Intrarenal or perinephric abscess
• Pregnant women - high risk for pyelonephritis - prenatal screening and treatment of asymptomatic bacteriuria
• Prostatic infection - in men.

EPEC - young children,

• outbreaks of infantile diarrhea in developing countries.
• Breast-feeding reduces the risk

symptoms develop after a brief incubation period (1 or 2 days).

• Diarrheal stool often contains mucus but not blood.
• Usually Self-limited (5–15 days),

Escherichia coli, Klebsiella, Proteus, Enterobacter, Serratia, Citrobacter, Morganella, Providencia, and Edwardsiella - components of the normal animal and human colonic flora

• In healthy humans, E. coli is the main gram-negative bacilli (GNB) in the colonic flora.
• In hospital settings, a variety of GNB emerge as the dominant flora of both mucosal and skin surfaces,

associated with:

• antimicrobial use,
• severe illness
• extended length of hospital stay.
• This colonization may lead to serious infection

References:

Enterotoxigenic E. Coli

Bacteremia

• Tropical or developing countries,

ETEC - major cause of endemic diarrhea

Traveler's diarrhea - 25–75% of cases.

After ingestion of contaminated water or food (poorly cooked, unpeeled, or unrefrigerated)

• Heat-labile toxin (LT) - structurally and functionally similar to cholera toxin
• Heat-stable toxin (ST) - fluid secretion in the jejunum and ileum.

Watery diarrhea accompanied by cramps.

• No mucus, blood, and inflammatory cells in stool, no fever.
• self-limited (lasting for 3 days),

infection may result in profound volume depletion in some cases

1. The Merck Manual of Diagnosis and Therapy - 19th Edition

2. Harrison's Principles of Internal Medicine - 18th edition

• Can arise from primary infection at any site.
• Percutaneous intravascular devices
• Trauma, burns

E. coli and S. aureus - two most common blood isolates in sepsis

• Sepsis-associated mortality rate - 30%
• Urinary tract (pyelonephritis)- the most common source of E. coli bacteremia
• The abdomen - second most common source,

Treatment: Extraintestinal E. Coli Infections

Cellulitis/Musculoskeletal Infection

• decubitus ulcers
• infection of ulcers of the lower extremity in diabetic patients

• Osteomyelitis
• infections of burn sites, surgical wounds - 10% of surgical infections

• Resistance is evolving rapidly
• The resistance to cephalosporins and TMP-SMX is increasing .
• Nitrofurantoin and fosfomycin - >90% of uncomplicated cystitis are susceptible

• Carbapenems and amikacin are the most active agents overall

Tigecycline and polymyxin B - for nearly pan-resistant isolates.

• Use the most appropriate narrower-spectrum agent whenever possible.

Treatment of UTI in females

Enteroinvasive E. Coli

Mild:

1. Nitrofurantoin - X2 for 5 days, or

2. TMP-SMX - X3 for 3 days, or

3. Fosfomycin - 3g single tablet

4. Ciprofloxacin, levofloxacin

Severely ill:

• Ceftriaxone, cefepime
• Ampicillin-sulbactam,
• Imipenem, Meropenem, doripenem
• ticaracillin - clavulanate

Enteroaggregative E.Coli (EAEC)

Diffusely Adherent (DAEC) E. Coli

A large amount of organisms is required for infection

• Developing countries
• Young children
• Traveler's diarrhea

Watery and sometimes persistent diarrhea in healthy and HIV-infected hosts.

EIEC shares many features with Shigella;

• incubation period of 1–3 days.
• Inflammatory colitis - fever, abdominal pain, tenesmus, and scant stool containing mucus, blood, and inflammatory cells.
• Symptoms are usually self-limited (7–10 days).

Diagnosis

• Strains of E. coli that cause extraintestinal infections grow aerobically and anaerobically in 24 h on standard media

• are easily identified
• > 90% of ExPEC strains - Rapid lactose fermenters

Diagnosis

distinguish noninflammatory from inflammatory cases

• STEC/EHEC - testing for Shiga toxins or toxin genes
• ETEC causes the majority and EAEC a minority of cases of noninflammatory traveler's diarrhea.
• ETEC, EPEC, and DAEC are uncommon causes of noninflammatory diarrhea

Treatment: Intestinal E. Coli Infections

all diarrheal syndromes - replacement of water and electrolytes.

• Traveler's diarrhea - early treatment with fluoroquinolone or azithromycin - decreases the duration of illness,

Loperamide may halt symptoms within a few hours.

STEC/EHEC infection

-grossly bloody diarrhea

- without fever

- antimicrobial therapy should be avoided,

• antibiotics increase the risk of HUS

The specific diagnosis rarely needed since the diseases are self-limited

• Empirical or symptom-based treatment plus rehydration

Mariam Kavtaria