Nonfermenting GN Rods & Miscellaneous GN Rods

MLAB 2434 – Microbiology 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,” “nonoxidizers”or nonsaccharolytic

General Characteristics of Nonfermenters (cont’d) Nonfermenters are ubiquitous in

the environment Predominantly opportunistic Also isolated in hospitals from

nebulizers, dialysate fluids, saline, and catheter devices

Somewhat resistant to disinfectants & antibiotics

The Nonfermenters

Achromobacter Acidovorax Acinetobacter Agrobacterium Alcaligenes Burkholderia Stenotrophomonas Chryseobacterium Chryseomonas Comamonas Flavimonas Flavobacterium

• Methylobacterium• Moraxella• Weeksekka• Ochrobactrum• Oligella• Pseudomonas• Psychrobacter• Roseomonas• Shewanella• Sphingobacterium

Clinical Infections

Septicemia Meningitis Osteomyelitis Wound infections following

surgery or trauma Nosocomial Infections

Clinical Infections

Risk factorsImmunosuppressionForeign body implantationTraumatic break in a host barrierAntibiotic therapyUnderlying disease

Initial Clues to Nonfermenters Long, thin gn rods or cb Oxidase positive (not ALL nonfermenters) No or slow growth of MacConkey agar Nonreactive in 24 hours on commercial

kit systems TSI nonreactive Resistant to antibiotics ( penicillin,

ampicillin & cephalosporins) Treat with aminoglycosides, quinolones and anti-

pseudomonal penicillins ( ticarcillin, piperacillin)

Nonfermenter Organization Nonfermenters are grouped

according to three characteristics Growth on MacConkey

• Not all nonfermenters grow on MAC• All nonfermenters that grow on MAC are lactose negative

Oxidase reaction OF test

Commonly Encountered Nonfermentative Organisms Pseudomonas characteristics

Associated with water and moist environments

• Not common as normal flora Strict aerobe GN rods or cb Usually motile with polar or polar tufts

of flagella Oxidase and catalase positive Usually grows on MacConkey agar Usually oxidizes carbohydrates

Pseudomonas aeruginosa:Clinical Infections

Types of infections• Bacteremia with ecthyma gangrenosum of

skin• Wound infections• Pulmonary disease (esp. in Cystic Fibrosis)• Nosocomial UTI• Endocarditis• Meningitis• Otitis externa (“swimmer’s ear”)• “Hot tub” syndrome (skin rash)

Pseudomonas aeruginosa:Virulence Factors

Endotoxins Hemolysins Cytotoxins Proteases Slime Pili

P. aeruginosa: Laboratory identification

Beta-hemolytic on blood agar Green metallic sheen due to

production of pigment pyocyanin (bluish-green)

Most strains also produce pigment pyoverdin (yellowish-green fluorescence)

Odor described as “grape-like” or “Frito-like”

Honorable mentions…

Pseudomonas fluorescens & Pseudomonas putida Produces pyoverdin but not pyocyanin Rarely causes clinical disease Found in water and soil, usually

environmental contaminants Pseudomonas stutzeri

Wrinkled, leathery colonies that may be light yellow or brown, non- fluorescent

Stenotrophomonas maltophilia

Third most common nonfermenter cultured, ubiquitous in nature

Common in the hospital environment

Implicated in infections of wounds, RT, UT and blood

Frequent isolate of Cystic Fibrosis patients

Other Nonfermenters

Acinetobacter – found in hospital environments; can cause opportunistic infection, skin/vaginal normal flora. On BAP transluscent-opaque, MAC colorless. On gram stain, short plump gncb

Burkholderia cepacia – most often associated with pneumonia in Cystic Fibrosis

Burkholderia pseudomallei – causes melioidosis( an aggressive pulmonary disease causing pneumonia, abscesses and septicemia)

Alcalingenes – found in water and resistant to disinfectants

References Engelkirk, P. G., & Duben-Engelkirk, J. (2008).

Laboratory Diagnosis of Infectious Diseases: Essentials of Diagnostic Microbiology . Baltimore, MD: Lippincott Williams & Willkins.

Kiser, K. M., Payne, W. C., & Taff, T. (2011). Clinical Laboratory Microbiology: A Practical Approach . Upper Saddle River, NJ: Pearson Education, Inc.

Mahon, C. R., Lehman, D. C., & Manuselis, G. (2011). Textbook of Diagnostic Microbiology (4th ed.). Maryland Heights, MO: Saunders.

http://www.microbelibrary.org/library/laboratory-test/2862-blood-agar-plates-and-hemolysis-non-fermenting-gram-negative-rods-including-pseudomonas-aeruginosa