Chapter 18 – Nonfermenting G- Rods & Miscellaneous G- RodsMLAB 2434 – Clinical MicrobiologyCecile 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
Nonfermenters make up 15% of all isolates of g- rods
Some common disease manifestations and risk factors for nonfermenters
Disease manifestations Septicemia Meningitis Osteomyelitis Wound infections following surgery or
trauma
Nonfermenter Clinical Infections (cont’d) Risk factors for nonfermenter
infectionImmunosuppressionForeign body implantationTraumatic 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 characteristicsGrowth on MacConkey Oxidase reactionOF test
Commonly Encountered Nonfermentative Organisms Pseudomonas characteristics
G- rods or cbUsually motile with polar or polar
tufts of flagellaOxidase and catalase positiveUsually grows on MacConkey
agarUsually 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)
• 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 “Frito-
like”
Commonly Encountered Nonfermentative Organisms (cont’d)
P. aeruginosa P. aeruginosa on MacConkey 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
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
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