non fermenting

• Fermentative or fermenters


  Organisms that ferment carbohydrates
• Nonfermentative or nonfermenters


  Organisms that do not ferment carbohydrates
• General characteristics of non-fermenters

  • Found in most environments—typically soil and water, on plants and decaying vegetation and in many foodstuffs
  • Prefer moist environments
  • Prefer and grow much better in an aerobic environment
  • Nonfermenting, long, thin gram-negative bacilli
  • Tend to be resistant to multiple classes of antibiotics
• Biochemical reactions of non-fermenters

  • Most group members are oxidase-positive
  • Some group members oxidize carbohydrates to derive energy for their metabolism— referred to as oxidizers
  • Some group members do not break down carbohydrates at all—referred to as nonoxidizers or asaccharolytic
  • Fail to acidify oxidative-fermentative (OF) media when overlaid with mineral oil
  • Fail to acidify triple sugar iron (TSI) agar butts
• Non-fermenters account for 15% of all gram-negative bacilli isolated from clinical specimens
• Non-fermenters are responsible for a number of serious infections (usually following surgery or trauma)
• Serious infections caused by non-fermenters

  • Septicemia
  • Meningitis
  • Osteomyelitis
  • Wound infections
• Biochemical characteristics that can indicate the presence of a nonfermenter in the clinical laboratory

  • Oxidase-positive (may be weak and variable)
  • Nonreactivity in 24 hours in commercial multitest kit systems
  • No acid production in the slant or butt of TSI agar or Kligler iron agar (KIA)
  • Resistance to a variety of classes of antibiotics
• Classification system for non-fermenters

  1. Growth on MacConkey (MAC) agar

  2. Oxidase reaction

  3. Glucose OF test
• Genera mostly seen in clinical lab

  • Pseudomonas aeruginosa
  • Acinetobacter spp.
  • Burkholderia spp.
  • Stenotrophomonas maltophilia
• Definitive ID


  • Usually reference lab using nucleic acid sequencing or mass spectrophotometric methods
  • Matrix-associated laser desorption–ionization time-of-flight (MALDI-TOF) ID of bacteria and fungi from colonies that is based on analysis of the unique spectra of their peptides when separated in the mass spectrophotometer
  • Mean time for ID is 6 min.
• Genus Pseudomonas


  • Accounts for largest percentage of all nonfermenters isolated from clinical specimens
  • Called Pseudomonads
  • Most members are gram-negative bacilli or coccobacillus, metabolized in strictly aerobic conditions, motile with polar flagellum or polar tuft of flagella, oxidase and catalase positive, usually oxidizer of carbohydrates
  • Usually grows on MAC agar
• Pseudomonas fluorescent group


  Includes Pseudomonas aeruginosa
• Pseudomonas aeruginosa


  • Found in moist environments like pools, hot tubs, catheters, and humidifiers in hospitals
  • Reservoirs include plants, soil, tap water
  • Uncommon part of normal bacterial microbiota
• Pseudomonas aeruginosa causes mild illness in healthy people and severe infections in those with weak immune systems
• Pseudomonas aeruginosa accounts for 5% to 15% of all nosocomial infections, especially pneumonia and bacteremia
• Clinical infections caused by Pseudomonas aeruginosa

  • Wound infections and burn patients
  • Pulmonary infections (cystic fibrosis [CF] patients)
  • Nosocomial urinary tract infections (UTIs) and bacteremias
  • Endocarditis
  • Ear infections
  • Skin rashes (hot tub syndrome)
• Prognosis and colonization factors for Pseudomonas aeruginosa


  • Poor prognosis factors include septic shock, granulocytopenia, inappropriate antimicrobial therapy, presence of septic metastatic lesions
  • Patients mechanically ventilated may quickly become colonized
• Virulence factors of Pseudomonas aeruginosa

  • Endotoxin (lipopolysaccharide [LPS])
  • Motility
  • Pili
  • Capsule
  • Flagella
  • Phospholipases
  • Type III secretion system
  • Several exotoxins (proteases, hemolysins, lecithinase, elastase, DNase)

  
• Colony morphology of Pseudomonas aeruginosa

  • β-hemolytic on sheep blood agar (SBA)
  • Flat spreading colonies with a characteristic metallic sheen
  • Produces pyoverdin (yellow-green or yellow-brown pigment) and pyocyanin (blue pigment)
  • Many strains produce a fruity, grapelike odor
• Identification characteristics of Pseudomonas aeruginosa


  • Green sheen on blood agar
  • Gram-negative bacilli
  • Oxidase and catalase positive
  • Oxidizes carbohydrates
  • Most are β-hemolytic
  • Arginine dihydrolase (ADH) positive
  • Growth at 42° C
  • Citrate positive
  • Grows on cetrimide agar

  
• Pseudomonas aeruginosa is innately resistant to many antimicrobial agents including penicillin, ampicillin, first- and second-generation cephalosporins, trimethoprim-sulfamethoxazole, chloramphenicol, and tetracycline
• Pseudomonas aeruginosa is typically susceptible to

  • Aminoglycosides
  • Semisynthetic penicillins (i.e., piperacillin and ticarcillin)
  • Third- and fourth-generation cephalosporins
• Pseudomonas fluorescens and Pseudomonas putida

  • Have low virulence
  • Isolated from respiratory specimens, contaminated blood products, urine, cosmetics, hospital equipment, and fluids
  • Can cause UTIs, postsurgical abscesses, empyema, septic arthritis, and wound infections
• Identification characteristics of Pseudomonas fluorescens and Pseudomonas putida

  • Produce pyoverdin, but neither produces pyocyanin
  • Do NOT grow at 42°C
  • Cannot reduce nitrate to nitrogen gas
  • Can produce acid from xylose
  • Gelatin hydrolysis: P. putida is negative, P. fluorescens is positive
• Treatment of Pseudomonas fluorescens and Pseudomonas putida

  • Susceptible to aminoglycosides, polymyxin, and piperacillin
  • Resistant to carbenicillin and trimethoprim/SMZ
• Pseudomonas stutzeri


  • Has rare, easily recognizable colony morphology - wrinkled, leathery, adherent colonies that may produce a light yellow or brown pigment
  • In the immunocompromised host, has been responsible for septicemia, meningitis in the HIV infected patient, pneumonia, endocarditis, postsurgical wound infections, septic arthritis, conjunctivitis, and UTIs
• Identification characteristics of Pseudomonas stutzeri

  • ADH (arginine dihydrolase) negative
  • Starch hydrolysis positive
• The organism grows well on MacConkey agar with lactose as the sole carbon source, producing pink colonies with green metallic sheen (green pigments are pyocyanin).
• Pseudomonas aeruginosa has a characteristic mucoid appearance due to the production of alginate by certain strains.
• P. aeruginosa is an opportunistic pathogen that can cause urinary tract, respiratory, wound, bloodstream, and eye infections.
• P. aeruginosa can be identified by its characteristic swarming motility.
• P. aeruginosa can be identified based on its ability to oxidize phenol red, which turns the medium bright orange-red.
• P. aeruginosa is resistant to colistin, gentamicin, imipenem, meropenem, and tetracyclines.
• P. aeruginosa is resistant to many antibiotics but susceptible to carbapenems, colistin, tigecycline, and polymixin B.
• P. aeruginosa produces a blue-green pigment called pyocyanin.
• P. aeruginosa is identified using biochemical tests such as oxidase test, citrate utilization, urease test, indole test, Voges-Proskauer test, methyl red test, and triple sugar iron agar.
• P. aeruginosa produces fluorescent pigments under UV light.
• P. aeruginosa is susceptible to carbapenems, cefepime, ceftazidime, chloramphenicol, doxycycline, fosfomycin, levofloxacin, minocycline, piperacillin, sulbactam, and trimethoprim/SMX.
• P. aeruginosa is oxidase positive and catalase positive.