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Gastrointestinal Gram Negative Rods Flashcards

1
Q

Gastrointestinal Gram Negative Rods

A

Gastrointestinal Gram Negative Rods

  • Gram negative bacilli that predominantly cause gastrointestinal infections (some may also cause extra-intestinal infections)
  • Gastrointestinal symptoms vary according to pathogen and may include:
    • **Diarrhea – watery / bloody **
    • Nausea, vomitting
    • Dehydration (as a consequence of fluid loss)
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2
Q

Gastrointestinal Gram Negative Rods

A

Gastrointestinal Gram Negative Rods

  • Some are normal flora in GI tract of humans/animals
  • Some are exclusive GI tract pathogens
  • Fecal contamination of food/water leads to gastrointestinal infections (exogenous source)
    • eg – Some species of Salmonella contaminate eggs, poultry
    • eg – person-to-person transmission of Shigella, fecal contamination of food (flies spread the contamination)
  • Extra-intestinal disease may occur when GNB gain access to other sites
    • Example – endogenous E.coli from the GI tract can cause urinary tract infection
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3
Q

Gastrointestinal Gram Negative Rods

A

Gastrointestinal Gram Negative Rods

  • Escherichia coli
  • Klebsiella
  • Proteus
  • Salmonella
  • Shigella
  • **Yersina **
  • Enterobacter
  • Citrobacter
  • Serratia
  • Morganella
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4
Q

Other Enteric GN rods

A

Other Enteric GN rods

Vibrio
Campylobacter
Helicobacter

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5
Q

Family “Enterobacteriaceae”

A

Family “Enterobacteriaceae”

  • Gram negative bacilli (rods)
  • Oxidase negative*
  • Facultative anaerobes
  • All ferment glucose
  • Vary in lactose fermentation*
    • Grown on MacConkey agar for differentiation
      • Lactose-fermentors - pink colonies
      • Non-lactose fermentors - transparent colonies
    • Also Eosin Methylene Blue agar (EMB)
  • Reduce nitrates to nitrites *
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6
Q

Coliform bacteria

A

Coliform bacteria

  • Facultatively anaerobic, Gram-negative rods
  • Commonly found in
    • soil, on plants, and on decaying vegetation
    • GI tract of animals
  • Colonize the intestinal tracts of animals and humans : “Coliforms”
    • Examples: Klebsiella, Citrobacter, Enterobacter, Serratia
    • Fecal coliform – E.coli

**One of the indicators of fecal pollution of water is the presence of E. coli *
Presence of coliforms in water is indicative of impure water and of poor sewage treatment **

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7
Q

Enterobacteriaceae - Virulence

A

Enterobacteriaceae - Virulence

  • Some are highly virulent (nearly always cause infection)
    • Example – Salmonella typhi, Shigella, Yersinia
  • Most are normal flora which are opportunistic
    • Example – E.coli, Klebsiella, Proteus
  • In some virulence depends on plasmid or bacteriophage that transfer bacterial genes coding for certain virulence factors
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8
Q

Enterobacteriaceae – cell components & virulence factors

A

Enterobacteriaceae – cell components & virulence factors

  • Lipopolysaccaharide (Lipid-A is endotoxin) *
  • Somatic (O) antigen
    • Cell wall antigens (shared among many different species)
  • Flagellar (H) antigen
    • Associated with motile species
  • Capsular (K) antigen
    • Polysaccharide capsules
    • Anti-phagocytic
  • O, H & K antigens are used for serological typing
  • Specific serotypes are associated with particular diseases
    • Eg – E.coli O157:H7 causes hemolytic uremic syndrome*
    • Eg – E.coli K1 – neonatal meningitis*
  • Other factors
    • Pili/fimbriae – adhesion factors
    • Exotoxins (eg. enterotoxins)
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9
Q

Enterobacteriaceae - Culture

A

Enterobacteriaceae - Culture

  • Categorization by lactose fermentation
    • Stool specimens for bacterial culture plated on MacConkey agar*
    • Eosin Methylene agar (EMB)
  • Bile salt tolerance
    • Tolerant to bile – Salmonella, Shigella – Hektoen enteric agar, Salmonella-Shigella agar
    • Intolerant - almost all other species
  • Other biochemical tests
    • Production of H2S, fermentation of sugars
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10
Q

Escherichia coli

A

Escherichia coli

  • GNB
  • Facultative anaerobe
  • Oxidase negative*
  • Lactose fermentor (pink colonies on MacConkey agar*) *
  • Reduces nitrates to nitrites *
  • Reservoir:
    • Human colon normal flora: may colonize urethra and vagina*
    • Contaminated crops (human feces as fertilizer)
    • Bovine (cattle) feces – harbour enterohemorrhagic strains (EHEC) *
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11
Q

Escherichia coli Transmission

A

Escherichia coli Transmission

  • Transmission may be:
    • Endogenous (from a persons’ own normal flora)
    • Fecal-oral
    • Maternal fecal flora
    • Enterohemorrhagic strains (EHEC) - bovine fecal contamination
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12
Q

Escherichia coli - Diseases

A

Escherichia coli - Diseases

  • Intestinal disease
    • Gastroenteritis*
  • Extra-intestinal diseases
    • Urinary tract infection*
    • Neonatal meningitis*
    • **Nosocomial (hospital-acquired) infections **
    • Septicemia *
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13
Q

E.coli - Gastroenteritis

A

E.coli - Gastroenteritis

  • E.coli is a major cause of diarrheal disease
  • Transmission: fecal-oral route
    • Contaminated food, water
  • 6 different strains of E.coli → 6 different mechanisms KNOW THEM
    • Enterotoxigenic E.coli (ETEC)
    • Enteropathogenic E.coli (EPEC)
    • Enterohemorrhagic E.coli (EHEC)
    • Enteroinvasive E.coli (EIEC)
    • Enteroadherent E.coli (EACE)
    • Diffusely adherent E.coli (DAEC)
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14
Q

Enterotoxigenic E.Coli (ETEC)

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Enterotoxigenic E.Coli (ETEC)

  • Endemic in developing nations
  • _Travellers’ diarrhea – those returning from regions of endemicity*_
  • 1-2 days incubation, persists 3-4 days
  • Acts of small intestine
  • Non-inflammatory diarrhea
    • Watery diarrhea *, cramps, nausea, occasional vomiting
  • Lab tests:
    • Will not be reported from stool cultures
    • Enterotoxin detection by immunoassay *
  • Treatment -
    • Rehydrate
    • TMP/SMX may shorten symptoms
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15
Q

ETEC – mechanism of action *

A

ETEC – mechanism of action *

  • **Prolonged hyper-secretion of CL- , Na+ ions and water by intestinal mucosal cells **
  • Decreased reabsorption of sodium

Produce 2 toxins:

  • LT *
    • Heat-labile toxin (LT-I and LT-II )
    • Similar to cholera toxin
    • Elevation of cAMP
  • ST *
    • Heat-stable toxin
    • Elevation of cGMP levels
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16
Q

Enteropathogenic E.Coli (EPEC)

A

Enteropathogenic E.Coli (EPEC)

  • Major cause of infant diarrhea in the 3rd world
  • Mechanism of action:*
    • _A/E lesions (Attaching & effacing) *_
    • EPEC attach to small intestine mucosal cells (using bundle-forming pili *) →efface (erase) brush-border microvilli → malabsorption→ watery diarrhea
  • Non-inflammatory diarrhea
  • Treatment: rehydration, antibiotics useful
  • Diagnosis:
    • Not reported from stool culture
    • Probes and assays to detect Bundle-forming pili *
  • Rehydration, Fluoroquinolones*
17
Q

Enterohemorrhagic E.Coli (EHEC) *

A

Enterohemorrhagic E.Coli (EHEC) *

  • Causes disease ranging from
    • **mild diarrhea **
    • severe bloody diarrhea (hemorrhagic colitis) *
    • Hemolytic Uremic syndrome (HUS) *
  • Found in GI tract of cattle
  • Transmission: fecal-oral, associated with
    • undercooked ground beef (hamburgers) *
    • Unpasteurized milk*
    • Unpasteurized cider/apple juice/juices*
  • _E.coli serotype O157:H7*_
  • E.coli serotype O104:H4
18
Q

EHEC (Enterohemorrhagic E.Coli) – mechanism of action*

A

EHEC (Enterohemorrhagic E.Coli) – mechanism of action*

  • Attaching & effacing lesions destroy microvilli
  • 2 toxins produced: _Shiga-like toxins *_ (STx1, STx2)
    • Receptors for toxin - intestinal villi and renal endothelial cells *
    • Destruction of intestinal villi – decreased absorption, increased secretion
    • Destruction of glomerular endothelial cells (Stx2)* – decreased filtration, renal failure
    • Inhibits protein synthesis by interfering with ribosomal subunit *

(note: EHEC also called VTEC–verotoxin E.coli)

19
Q

EHEC (Enterohemorrhagic E.Coli) disease

A

EHEC (Enterohemorrhagic E.Coli) disease

  • 50% of patients - vomiting
  • Mild diarrhea
  • Progresses to _bloody diarrhea*_
  • Lab ID:
    • EHEC - _non-fermentors of sorbitol *_
    • Detected on Sorbitol MacConkey agar (SMAC)
  • Treatment:
  • Rehydrate
  • **Avoid antibiotics **
    • Antibiotics increase risk of HUS *
20
Q

EHEC – Hemolytic Uremic syndrome

A

EHEC – Hemolytic Uremic syndrome

  • Characterized by
    • Acute renal failure*
    • thrombocytopenia
    • Microangiopathic hemolytic anemia (Hb decreased)
  • Occurs in 10% of EHEC cases – usually children 5-10 yrs and younger*
  • Fatal in 3 – 5% cases
  • Serious sequelae – in 30% cases
    • Renal impairment
    • hypertension
21
Q

Enteroinvasive E.coli (EIEC)

A

Enteroinvasive E.coli (EIEC)

  • Inflammatory diarrhea
    • Similar to Shigellosis
  • _Fever with blood and mucous in stool (dysentery) *_
  • Mechanism of action:
    • Invasion of epithelial cells of colon
    • Invade and destroy epithelial cells* → diarrhea with some blood due to invasion
    • Produce hemolysin (lysis of RBCs)
  • Fever, cramps, bloody diarrhea with mucous
    • RBCs and leukocytes detected in stool *
  • Treatment : Rehydrate
22
Q

Enteroaggregative E.coli - EAEC

A

Enteroaggregative E.coli - EAEC

  • **Persistent watery diarrhea **
  • Infants & young children – developing nations
  • Adherence to intestinal cells via aggregative adherence fimbriae →shortening of microvilli – _stacked brick* appearance of GN rods_
  • Treatment: rehydrate
  • **(NOTE: hybrid strain of EAEC – producing shiga-like toxin (plasmid-encoded) identified that cause an outbreak of E.coli gastroenteritis in Germany 2011, many cases of HUS, some fatal) **
23
Q

Diffusely adherent E.coli - DAEC

A

Diffusely adherent E.coli - DAEC

  • Watery diarrhea
  • Infants – 5 yrs
  • Adherent, elongation of microvilli
24
Q

E.coli diarrhea – lab diagnosis

A

E.coli diarrhea – lab diagnosis

  • E.coli is endogenous gut flora
  • Strains causing diarrhea are acquired from outside sources (exogenous)
  • Stool cultures in lab grow both
    • All E.coli are lactose-fermentors (pink colonies MA)
    • Need special tests for detecting toxin-production
  • Therefore labs will not report E.coli from stool cultures
    • Do not expect the lab to send culture reports for EPEC, ETEC, etc
  • Only EHEC (plated on sorbitol MA) will be reported from bloody stool specimens*
  • EHEC do not ferment sorbitol
  • Immunoassays for toxin detection, PCR to detect gens targets in clinical specimens
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E.coli causes what most commonly
E.coli - UTI * _**Most common cause of UTI\***_ including cystitis (bladder infection) and pyelonephritis (involving kidneys) * **Source: endogenous fecal flora** * Transmission * Colon → urethra → bladder → may go up to kidneys (ascending UTI) * Strains possess **P-pili (fimbriae) \*** – **adherence factor** * **Incidence of UTI higher in females** * Honeymoon cystitis – incidence of UTI associated with increased sexual activity in females
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E.coli - UTI symptoms
E.coli - UTI symptoms Symptoms * **Urethritis: burning on urination** * **Cystitis** * pelvic pressure * lower abdominal discomfort * **frequent painful urination (dysuria or painful micturition)** * blood in urine (hematuria) * **Pyelonephritis** * **upper back and side (flank) pain** * **High fever** * Shaking and chills * nausea, vomitting
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E.coli – UTI diagnosis and treatment
E.coli – UTI diagnosis Specimen: **Urine (turbid)** * **Urinalysis – Dipstick test** * Detects presence of blood * **leukocyte esterase (suggestive of WBCs) \*** * **Nitrites (suggestive of coliform bacteria)** * **Urine culture** * Clean-catch midstream urine plated on **MacConkey** agar and blood agar * A report of **\>10^5** **CFUs** (colony forming units) shows **significant bacteriuria \*** * **Antibiotic susceptibility test (AST) report** helpful in choice of antibiotic (in case of drug resistant UTI cases) * Treatment: **fluoroquinolones (norfloxacin), TMP-SMX \***
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E.Coli - Neonatal meningitis \*
E.Coli - Neonatal meningitis \* * Neonates and upto 2 months of age * **Source of E.coli: maternal fecal flora during birth** * **E.coli K1 serotpye** * Symptoms: * **Sudden onset of fever, lethargy, vomiting** * **Bulging fontanelle (soft spot on head)** * **Paradoxical irritation** * Lab tests: * Gram stain – neutrophils + gram-negative bacilli * Detection of capsular antigen * Treatment: * Cephalosporin - ceftriaxone note: Leading causes of neonatal meningitis 1. Streptococcus agalactiae (group B Strept) 2. Escherichia coli 3. Listeria monocytogenes (rare)
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E.Coli – Other infections
E.Coli – Other infections * **Hospital-acquired** (nosocomial) infections * **Septicemia** – bacteria in bloodstream * which can lead to endotoxic shock – may be fatal * Source of E.coli: usually from UTI or GI tract * **Pneumonia** * **Wound infections**
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Klebsiella
Klebsiella Gram-negative bacilli, Klebsiella pneumoniae, isolated from a lung abscess in a patient with pneumonia * Imp. Species – **K. pneumoniae** * **Mucoid, lactose + (pink on MA)\*** * **Prominent capsule** * Reservoir: moist environments, colon * **_Community-acquired lobar pneumonia_** * **alcoholics, aspiration \*** * **“currant-jelly” sputum** (thick, viscous) \* * (note: Strept. pneumoniae is most common cause of community-acquired lobar pneumonia) * **_Ventilator-associated pneumonia_** * **_Catheter-related UTI_** * **Due to fecal contamination of catherters** * **Abcess formation** \* in pneumonia and other infections * **Treatment: difficult due to** * **Abcess formation** * **Multidrug resistance** * **3rd generation cephalosporin with or without an aminoglycoside\***
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Proteus
Proteus * 2 species - P.mirabilis, P.vulgaris * Important features * **Non-lactose fermenting (colourless cols) \*** * **“swarming” growth \*** * **_Urease_ produced\*** * Breakdown of urea to ammonia → alkalization * Alkalization → precipitation of magnesium (struvite crystals) and calcium (apatite crystals) → **kidney stones** * _**UTI\***_ * _**Struvite kidney stones – Staghorn renal calculi\***_ * **Treatment: \*** * **Fluoroquinolones** * **TMP-SXM** * **3rd generation cephalosporins**
32
Serratia marcescens
Serratia marcescens * **Gram negative rod, oxidase negative** * **Red pigment producer – Prodigiosin\*** * “**Salmon-red” pigment** * Cultures grown at **room temperatures** * Habitat: commonly found in environment * Colonization of **hospitalized patients \*** * Infections * **Burn-related wound infections** * **Hospital-acquired pneumonia** * **UTI (catheter-related)** * **Septicemia, Meningitis, endocarditis** * **Osteomyelitis – common in Chronic granulomatous disease in infancy \*** * Remember **RED PIGMENT !! \***
33
Shigella
Shigella * Non-lactose fermentor * MacConkey agar * Non-motile\* * Stool microscopy – RBCs + Fecal leukocytes * _**Bloody diarrhea (“Bacillary” dysentery) \***_ * **Inflammatory diarrhea** * Tranmission**: fecal-oral** * **Person-to-person \***, inadequate hand-washing * **Flies, contaminated food/water** * **Humans** are **only host** for Shigella \* * Highly virulent : **low infective dose 10-100 bacilli \*** * Outbreaks seen in * **daycare centers, nurseries, long-term care facilities\*** * **Also among men who have sex with men (MSM) \***
34
Clinical case - Shigellosis
Clinical case - Shigellosis * In 2005, 3 states in the US reported outbreaks of multidrug-resistant Shigella infections in **daycare centers**. * 532 infections were reported in Kansas city area, with median age of patients 6 years old. * The predominant pathogen was MDR strain of **Shigella sonnei**. 89% of isolates were **resistant to ampicillin and TNP-SMX.** * Shigellosis spreads easily in daycare centers because of increased risk of **fecal contamination** and the **low infectious** dose required. * Parents, teachers as well as classmates, are at significant risk for disease.
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Shigella – 4 species
Shigella – 4 species * **S.sonnei \*** * **Most common in US** * **_S.dysenteriae_** * Most severe infection * **Shiga-toxin (similar to EHEC) \*** * **HUS (hemolytic uremic syndrome) \*** * S.flexneri * S.boydii
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Shigella – pathogenesis \*
Shigella – pathogenesis \* * Shigella **invade** and **destroy cells of large intestine and rectum\*** * Fever, **severe abdominal cramps, tenesmus (straining to defecate)** * **Small amounts of stool with frank blood and pus \*** * Self-limited * In addition **some species produce Shiga toxin\*** * Similar to Shiga-like toxins of EHEC\* * Damages glomerular endothelium → **HUS\*** * **Shiga toxin: Mechanism of action \*** * AB toxin * B subunit binds to receptors on intestinal cells * A subunit enters cells **→ cleaves 60S ribosome subunit → stops protein synthesis \*** * Intestinal cells die
37
Shigella – Clinical disease
Shigella – Clinical disease * _**Bloody diarrhea (dysentery) \***_ * _Extra-gastrointestinal complications_ * _**Hemolytic uremic syndrome (HUS) \***_ * **Seizures** (10% cases) – nonrecurring and uncomplicated * **Reactive arthritis (Reiter syndrome) \*** may occur * Triad of arthritis, urethritis and conjunctivitis * 2 to 4 weeks after infection with Shigella * Mostly in men 20-40 yrs
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Identify Shigella
Identify Shigella * Belongs to Enterobacteriaceae therefore - * Gram negative rod, oxidase negative * **Non-motile\*** * **Non-lactose-fermenting on MA \*** * Stool cultured on selective media * **Hektoen enteric agar** (supresses normal gut flora, allow Shigella, Salmonella to grow) * **Treatment: shortens course of disease \*** * **Empiric - Fluoroquinolone or TMP-SMX** * **Check antibiotic susceptibility reports to ascertain resistant**
39
Enterobacter, Citrobacter, Morganella
Enterobacter, Citrobacter, Morganella * **Common nosocomial infections\* (esp. ICU)** * **UTI** * **Wound / soft tissue infections** * **Pulmonary infections** * These organisms can be very resistant to many antibiotics

Microbiology Block 2 (17 decks)

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