Nonfermenters
(Those that are Gram-negative
bacilli)
Nonfermenters

Nonfermenters are found in nature as
inhabitants of soil and water and as harmless
parasites on the mucous membranes of man
and other animals.
 Nonfermenters can cause disease when they
colonize and subsequently infect
immunocompromised individuals or when they
gain access to a normally sterile body site
through trauma.
Nonfermenters
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Nonfermenters only comprise a small
percentage of the total clinical isolates, but
they require more effort for identification.
 Classification
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No family designation
Includes many genera whose names are
continually changing
By definition they do not ferment glucose
Morphology and cultural characteristics
Nonfermenters
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Gram-negative bacilli (g-b) or coccobacilli (g-cb)
Most are nonfastidious and are isolated by the
same means used to isolate the
Enterobacteriaceae.
Some grow on a Mac plate and others do not
On CBA plates, morphology, size, hemolytic activity,
and pigmentation may provide valuable information
for identification
Gram stain - Acinetobacter
P. aeruginosa – green pigment
P. aeriginosa
Nonfermenters
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They are obligate aerobes and most will not grow
or will grow poorly under anaerobic conditions.
Some require 48-72 hours for growth
Most grow best at 370 C, but a few grow better at
RT (Pseudomonas fluorescens and Pseudomonas
putida)
Biochemistry and identification
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Initial clues that an organism is a NF include
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Lack of glucose fermentation (TSI= K/K)
May be oxidase +
Nonfermenters
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May fail to grow on a Mac plate
May be unusually resistant to antibiotics
Additional testing – must identify the method or
scheme to be used
The frequency of isolation of the different NF is
used to select tests that will best be able to identify
the most commonly isolated organisms (those that
you looked at in the lab).
What is the most commonly isolated NF?
Nonfermenters
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The CDC scheme of identification separates
organisms into 8 groups based on:
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Growth versus no growth on Mac
Oxidase test results
O/F results
Further testing might include:
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Motility (by polar flagella)
Nitrate reduction or denitrification
Urease production
Esculin hydrolysis
Indole – use Ehrlichs rather than Kovacs reagent because
Ehrlichs is more sensitive
Nonfermenters
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Rapid decarboxylation reactions
Pigment production
growth in cetramide
Phenylalanine deaminase
Growth at 420 C
Virulence factors that are extracellular
products (Pseudomonas aeruginosa)
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Expression is under control of two component
signal transduction, quorum sensing systems.
When the bacteria detects a critical concentration
of an autoinducer released by the organism, a
signal transduction cascade will trigger the
expression of these products:
Quorum sensing
Nonfermenters
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Elastolytic proteases
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Alkaline proteases
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Elastin is a constituent of lung tissue and blood vessels.
The damage caused by the elastotytic proteases causes
an inflammatory reaction that compromises the host and
aids in the dissemination of the organism.
These proteases may degrade complement and IgA, thus
hindering the immune response.
Exotoxin A (iron limitation also contributes to
inducing its expression) which is the most toxic
product produced by Pseudomonas aeruginosa.
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It is cytotoxic for eukaryotic tissue culture cells and lethal for
many mammals (LD50 in mice= 60-80 ng.).
The mechanism of action is to interfere with protein
synthesis by ADP-ribosylation of elongation factor 2.
The liver is a prime target for this toxin.
Nonfermenters
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Exotoxin S – ADP-ribosylates vimentin, a structural
component of the host cell, and GTP-binding
proteins
Phospholipase C – a hemolysin that may be
involved in the breakdown of phospahtidyl choline,
a major surfactant of the lung, leading to pulmonary
collapse.
Leukocidin
Pyocyanin- a secreted pigment that is toxic due to
its involvement in the generation of reactive oxygen
intermediates (superoxide radical and hydrogen
peroxide)
Nonfermenters
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Virulence factors – (P. aeruginosa ) cell
surface:
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Both pilin and non-pilus adhesions are important for
attachment
LPS – endotoxin
Iron capturing ability
Flagella
Alginate synthesis
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Forms a viscous gel around the bacteria
May function as an adhesion and may also function to
prevent phagocytosis
Antimicrobic resistance – due to outer membrane
changes
Polar flagella of P. aeruginosa
Nonfermenters
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Virulence factors – Burkholderia
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Produce exotoxins
Clinical significance
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Pseudomonas aeruginosa (most frequently isolated
NF)
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Is a major cause of nosocomial infections
Commonly found in burn wounds
Is associated with chronic pulmonary disease in patients
with cystic fibrosis (these patients have a dysfunction of
the exocrine glands result in secretion of abnormal viscid
mucous) where very mucoid isolates are usually isolated.
Mucoid strains of P. aeruginosa in
cystic fibrosis patient
Nonfermenters
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Cause 70% of otitis externa (swimmer’s ear)
Dermatitis associated with contaminated whirlpool baths
Stenotrophomonas maltophilia (second most
frequently isolated NF)
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Is part of the transient NF of hospital patients and causes
a wide variety of nosocomial infections
Is sxt sensitive
Nonfermenters
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Acinetobacter
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Chryseobacterium meningosepticum
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Occasionally found causing meningitis and septicemia
Moraxella
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Is found in soil and water and as part of the skin NF
Is a common colonizer and less commonly a cause of
nosocomial infections
M. lacunata causes conjunctivitis and keratitis in the
malnourished alcoholic population
Burkholderia – two species are true pathogens
Nonfermenters
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B. pseudomallei
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Causes melioidosis, a disease seen primarily in southeast
Asia where it is a normal inhabitant of soil and water.
The disease is acquired through contamination of
wounds or via inhalation or ingestion.
The disease may range from unapparent, to chronic or
acute pulmonary infection, to overwhelming septicemia
with multiple abscesses in many organs
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B. mallei
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Causes glanders in equines.
Humans occasionally acquire the disease by contact with
infected nasal secretions of equines, through abrasions and
occasionally through inhalation.
Used to be a problem in the military when horses where
used.
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Nonfermenters
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The disease may manifest as a chronic pulmonary
disease, as a form characterized by multiple
abscesses of the skin, subcutaneous tissue, and
lymphatics (Farcy), or as an acute, fatal
septicemia.
Antimicrobial susceptibility
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Antimicrobial suseptibility testing is essential
since these organisms tend to be even
more resistant than the Enterobacteriaceae.