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