Chapter 18 –
Nonfermenting GRods & Miscellaneous
G- Rods
MLAB 2434 – Clinical Microbiology
Cecile Sanders & Keri Brophy-Martinez
General Characteristics of
Nonfermenters
Nonfermentative organisms that
break down carbohydrates
oxidatively (aerobically) are also
called “oxidizers” or “saccharolytic”
 Organisms that are NOT able to
break down carbohydrates
fermentatively or oxidatively are
called “biochemically inert” or
“nonoxidizers”

General Characteristics of
Nonfermenters (cont’d)
Nonfermenters are ubiquitous in
the environment
 Also isolated in hospitals from
nebulizers, dialysate fluids, saline,
and catheter devices
 Somewhat resistant to
disinfectants

Nonfermenter Clinical
Infections
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Nonfermenters make up 15% of all
isolates of g- rods
Some common disease manifestations and
risk factors for nonfermenters
Disease manifestations
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Septicemia
Meningitis
Osteomyelitis
Wound infections following surgery or
trauma
Nonfermenter Clinical
Infections (cont’d)

Risk factors for nonfermenter
infection
Immunosuppression
 Foreign body implantation
 Traumatic break in a host barrier

Biochemical Characteristics
of Nonfermenters
Nonfermenters vary in biochemical
and morphologic characteristics
 All are nonreactors on TSI slants
 Oxidative vs. fermentative
properties can be demonstrated
with use of OF
(oxidative/fermentative) medium

Initial Clues to
Nonfermenters
Long, thin g- rods or cb
 Oxidase positive (not ALL
nonfermenters)
 Nonreactive in 24 hours on
commercial kit systems
 TSI nonreactive
 Resistant to antibiotics

Nonfermenter
Organization

Nonfermenters are grouped
according to three characteristics
Growth on MacConkey
 Oxidase reaction
 OF test

Commonly Encountered
Nonfermentative Organisms

Pseudomonas characteristics
G- rods or cb
 Usually motile with polar or polar
tufts of flagella
 Oxidase and catalase positive
 Usually grows on MacConkey agar
 Usually oxidizes carbohydrates

Commonly Encountered
Nonfermentative Organisms
(cont’d)

Pseudomonas aeruginosa
• Most common nonfermenter isolated
from clinical specimens
• Not common as normal flora
• Types of infections
• Bacteremia with ecthyma gangrenosum of
skin
• Wound infections
• Pulmonary disease (esp. in Cystic Fibrosis)
Commonly Encountered
Nonfermentative Organisms
(cont’d)
• Types of Infections for P. aeruginosa
(cont’d)
•
•
•
•
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Nosocomial UTI
Endocarditis
Meningitis
Otitis externa (“swimmer’s ear”)
“Hot tub” syndrome
• Virulence factors for P. aeruginosa
• Endotoxins, hemolysins, proteases, slime,
etc.
Commonly Encountered
Nonfermentative Organisms
(cont’d)
• P. aeruginosa identifying
characteristics
• Beta-hemolytic on blood agar
• Green metallic sheen due to production of
pigment pyocanin (green)
• Most strains also produce pigment
pyoverdin (blue)
• Odor described as “grape-like” or “Fritolike”
Commonly Encountered
Nonfermentative Organisms
(cont’d)
P. aeruginosa
on MacConkey
P. aeruginosa
producing procyanin
Commonly Encountered
Nonfermentative Organisms
(cont’d)

Pseudomonas fluorescens &
Pseudomonas putida
• Produces pyverdin but not pyocyanin
• Rarely causes clinical disease

Stenotrophomonas maltophilia
• Third most common nonfermenter
cultured
• Common in the hospital environment
Other Nonfermenters
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Acinetobacter – found in hospital environments; can
cause opportunistic infection
Pseudomonas stutzeri – wrinkled, leathery colonies
that may be light yellow or brown
Burkholderia cepacia – most often associated with
pneumonia in Cystic Fibrosis
Burkholderia pseudomallei – causes melioidosis
Alcalingenes – found in water and resistant to
disinfectants