Gram%20Negative%20Rods

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Gram Negative Rods

• Enterobacteriaceae (Coliforms)

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(No Transcript)
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Citrobacter freundii
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Citrobacter freundii

• Uses citrate as their sole source of carbon.
• These bacteria can be found almost everywhere in
  soil, water, wastewater, etc. It can also be
  found in the human intestine.
• They are rarely the source of illnesses, except
  for infections of the urinary tract and infant
  meningitis.

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Citrobacter freundii
Motility negative MR positive
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Escherichia coli
Motile species
Non-motile species
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Escherichia coli
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Escherichia coli

• One of the main species of bacteria living in the
  lower intestines of mammals, known as gut flora.
• There are about 1 trillion excreted in the feces
  daily.
• However, the bacteria are not confined to this
  environment, and specimens have also been
  located, for example, on the edge of hot springs.
  
• The E. coli strain O157H7 is one of hundreds of
  strains of the bacterium that causes illness in
  humans.
• E. coli are unable to sporulate. Thus, treatments
  which kill all active bacteria, such as
  pasteurization or simple boiling, are effective
  for their eradication, without requiring the more
  rigorous sterilization which also deactivates
  spores.

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Escherichia coli

• E. coli can generally cause several intestinal
  and extra-intestinal infections such as urinary
  tract infections, meningitis, peritonitis,
  septicemia and pneumonia.
• Although it is more common in females due to the
  shorter urinary tract, urinary tract infection is
  seen in both males and females. Poor toilet
  habits can predispose to infection (doctors often
  advise women to "wipe front to back, not back to
  front") but other factors are also important
  (pregnancy in women, prostate enlargement in
  men).
• If E. coli bacteria escape the intestinal tract
  through a perforation (a hole or tear, for
  example from an ulcer, a ruptured appendix, or a
  surgical error) and enter the abdomen, they
  usually cause peritonitis that can be fatal
  without prompt treatment. However, E. coli are
  extremely sensitive to such antibiotics as
  streptomycin or gentamycin.

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Escherichia coli

• Certain strains of E. coli, such as Escherichia
  coli O157H7, produce a toxin and can cause food
  poisoning usually associated with eating cheese
  and contaminated meat (contaminated during or
  shortly after slaughter or during storage or
  display).
• The usual countermeasure is cooking suspect meat
  "well done" the alternative of careful
  inspection of slaughtering and butchering methods
  (to make sure that the animal's colon is removed
  and not punctured).

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Escherichia coli

• Escherichia coli O157H7 is the strain is
  believed to be associated with the 2006 United
  States E. coli outbreak linked to fresh spinach.
  Severity of the illness varies considerably it
  can be fatal, particularly to young children, the
  elderly or the immunocompromised
• E. coli are susceptable to amoxicillin,
  cephalosporins, aminoglycosides, streptomycin, or
  gentamycin.
• Antibiotic resistance is a growing problem. Some
  of this is due to overuse of antibiotics in
  humans, but some of it is probably due to the use
  of antibiotics as growth promoters in food
  animals.

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Escherichia coli
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Enterobacter aerogenes
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Enterobacter aerogenes

• Several strains of the these bacteria are
  pathogenic and cause opportunistic infections in
  immunocompromised (usually hospitalized) hosts.
• The urinary and respiratory tract are the most
  common sites of infection.
• Enterobacter can be distinguished from other GNR
  by virtue of being a 'fast fermenter' of lactose
  (as are E. coli and Klebsiella).

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Enterobacter
Methyl Red negative


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Klebsiella pneumoniae
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Klebsiella pneumoniae

• This is a nonmotile, encapsulated,
  lactose-fermenting, and facultatively anaerobic
  organism.
• It is found in the normal flora of the mouth,
  skin, and intestines.
• It naturally occurs in the soil and about 30 of
  strains can fix nitrogen in anaerobic conditions.

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Klebsiella pneumoniae

• K. pneumoniae can cause bacterial pneumonia,
  typically due to aspiration by alcoholics, though
  it is more commonly implicated in
  hospital-acquired urinary tract and wound
  infections, particularly in immunocompromised
  individuals.
• Klebsiella ranks second to E. coli for urinary
  tract infections in older persons.
• Feces are the most significant source of patient
  infection, followed by contact with contaminated
  instruments.
• Klebsiella is resistant to ampicillin but
  susceptible to aminoglycosides and
  cephalosporins.

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Klebsiella pneumoniae
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Proteus vulgaris
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Proteus vulgaris

• Responsible for many human urinary tract
  infections.
• Proteus species do not ferment lactose, are
  oxidase negative, and urease positive some
  species are motile.

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Proteus vulgaris
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Providencia stuartii
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Providencia stuartii

• This organism is motile.
• They are opportunistic pathogens in humans and
  can cause urinary tract infections, particularly
  in patients with long-term indwelling urinary
  catheters or extensive severe burns.
• Some strains are sensitive to ampicillin.

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Providencia stuartii
IMViC - ODC - ONPG H2S - Mannitol -
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Salmonella enterica
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Salmonella enterica
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Salmonella enterica

• This organism causes typhoid fever and foodborne
  illness.
• Salmonella species are motile and produce
  hydrogen sulfide.
• They usually do not ferment lactose.

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Salmonella enterica

• Food poisoning from Salmonella is usually from
  poultry and raw eggs and from food that has been
  cooked or frozen, and not eaten straight away.
• The overuse of antibiotics in both the poultry
  and beef industries have created a strain of
  salmonella which is potentially resistant to
  antibiotics.
• It can also be caught by handling reptiles, such
  as iguanas.

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Salmonella enterica

• The prevention of Salmonella as a food illness
  involves effective sanitizing of food contact
  surfaces.
• Alcohol has proven to be an effective topical
  sanitizer against Salmonella.

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Salmonella enterica
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Shigella somnei
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Shigella somnei

• This organism is non-motile, non-spore forming.
  It is H2S positive.
• It is the causative agent of human shigellosis.
• Shigella infection is typically via ingestion
  (fecaloral contamination).
• 10 bacterial cells can be enough to cause an
  infection.

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Shigella somnei

• The stool may contain blood, mucus, or pus (eg
  dysentery).
• Shigella cause dysentery that results in the
  destruction of the epithelial cells of the
  intestine.
• Some strains produce an enterotoxin similar to E.
  coli O157H7
• Symptoms usually begin two to four days after
  ingestion. Symptoms usually last for several
  days, but can last for weeks.
• Severe dysentery can be treated with ampicillin.

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Shigella somnei

• IMViC - - - or - -
• ODC or -
• LDC -
• Urease -
• H2S -
• Sucrose -
• TSI K/A

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Serratia marcescens
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Serratia marcescens

• This organism is involved in nosocomial
  infections, particularly urinary tract infections
  and wound infections.
• It is motile.
• Due to its preference for damp conditions, it is
  commonly found growing in bathrooms (especially
  on tile grout), where it manifests as a pink
  discoloration.
• Once established, complete eradication of the
  organism is often difficult, but can be
  accomplished by application of a bleach-based
  disinfectant.

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Serratia marcescens

• S. marcescens can cause conjunctivitis and tear
  duct infections.
• It is common in the respiratory and urinary
  tracts of adults and the gastrointestinal system
  of children.

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Serratia marcescens

• IMViC - or - -
• LDC
• ARA -
• ORN

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Sample Flowchart for Lactose Negative organisms
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Lactose Negative

• Perform an Indole test
• Positive
• Proteus vulgaris (H2S negative)
• Providencia stuartii (H2S positive)
• E. coli (Citrate negative)
• Citrobacter freundii (H2S positive, Citrate
  positive)
• Negative
• Perform a urease test (all should be negative)
• Perform the MR-VP test

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Urease negative

• Perform a motility test
• Positive
• Salmonella enterica (H2S positive)
• Serratia marcescens (H2S negative)
• Negative
• Shigella somnei

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MR-VP Tests

• /-
• Citrobacter freundii
• -/
• Klebsiella pneumoniae (non-motile)
• Enterobacter aerogenes (motile)