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Microbiology Block 2 > Gastrointestinal Gram Negative Rods > Flashcards

Gastrointestinal Gram Negative Rods Flashcards

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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)

A

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
25
Q

E.coli causes what most commonly

A

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
26
Q

E.coli - UTI symptoms

A

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
27
Q

E.coli – UTI diagnosis and treatment

A

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 *
28
Q

E.Coli - Neonatal meningitis *

A

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)
29
Q

E.Coli – Other infections

A

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
30
Q

Klebsiella

A

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*
31
Q

Proteus

A

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
Q

Serratia marcescens

A

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
Q

Shigella

A

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
Q

Clinical case - Shigellosis

A

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.
35
Q

Shigella – 4 species

A

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
36
Q

Shigella – pathogenesis *

A

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
Q

Shigella – Clinical disease

A

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
38
Q

Identify Shigella

A

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
Q

Enterobacter, Citrobacter, Morganella

A

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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