Gram negative rods – Non-fermenters
– General characteristics
• Acinetobacter and Stenotrophomonas
– non-fermenters of glucose
– NLF on Mac
– oxidase-negative
• Pseudomonas and Burkholderia
– non-fermenters of glucose
– NLF on Mac
– oxidase-positive
– Epidemiology
• All are widely distributed in nature
• All do well in moist, hospital environments
• All are opportunistic pathogens, important in nosocomial
infections.
• B. cepacia can colonize and infect cystic fibrosis patients
• Mainly acquired during long or frequent hospitalizations
– Pathogenesis
• Acinetobacter and Stenotrophomonas
– virulence factors unknown
– intrinsic and acquired multi-drug resistance
– respiratory tract, soft tissue/wound infections, bacteremia
• Burkholderia
– largely unknown, ? binding to resp. mucin in CF patients
– intrinsic resistance to antibiotics
– respiratory tract, soft tissue/wound infections, bacteremia
• Pseudomonas
– exotoxins, proteolytic enzymes, alginate
– acquired multi-drug resistance to antibiotics
– respiratory tract, soft tissue/wound infections, bacteremia
– Laboratory Diagnosis
• Specimen collection, transport, and processing
– no special considerations
• Direct detection methods
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–
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Acinetobacter: plump coccobacillary GNR
Stenotrophomonas: short, straight GNR
Burkholderia: med., straight GNR
Pseudomonas: med., straight GNR
• Culture
– All grow well on BAP, CAP, Mac
– PC/BC agar for Burkholderia
» selective media for B. cepacia; color of colonies varies
with media formulation
• Testing on automated systems
– ID and sens testing of NFs on automated systems can be
problematic
– Isolates from CF patients are always tested manually
Acinetobacter on Gram stain
http://www.rivm.nl/infectieziektenbulletin/bul122/scan12.gif
Stenotrophomonas on Gram stain
http://www.buddycom.com/bacteria/gnr/xanmalt2_5.jpg
Pseudomonas on Gram stain
http://www.bact.wisc.edu/Bact330/P.aeruginosa.jpeg
Pseudomonas on solid media
http://www.silvermedicine.org/colloidalsilverstudytexas.html
Burkholderia on PC Agar
http://www.troybio.com/images/Product_Images_BBL/BBL.htm
– Laboratory Diagnosis
• Colony appearance
– Acinetobacter: gray, smaller than enterics; may look purple
on Mac
– Stenotrophomonas: Larger than Acinetobacter; smells like
ammonia
– Pseudomonas: green, flat, spready, hemolytic; smells like
grapes
» mucoid in CF patients
» pyocyanin: green pigment
– Burkholderia: smooth gray
• Identification:
– Acinetobacter and Stenotrophomonas: oxidase neg., nonenteric looking gnr on gram stain; ID by API non-ferm;
Acinetobacter ID on VITEK2
– Pseudomonas: colony morph; Gram stain; oxidase pos;
growth at 42C; pigment production; glucose oxidizer
– Burkholderia: screening resp. specimens from CF patients
only; all cultures get PC agar
– Susceptibility testing and therapy
• Acinetobacter:
–
–
–
–
test if clinically significant
resistance among classes, so results guide therapy
KB and MIC
various treatment options
• Stenotrophomonas:
–
–
–
–
test if clinically significant
multiply resistant so Rx can be limited
in vitro results to beta-lactam drugs are unreliable
Trim/Sulf is primary treatment option
• Pseudomonas:
– susceptibility results guide therapy
– can be highly resistant
– usually treat with anti-Pseud beta lactam + an
aminoglycoside because resistance develops quickly
• Burkholderia:
– No valid testing methods or interpretive guidelines
– treat empirically with pip, ceftaz, imipenem but organism is
rarely eradicated