8.) Pseudomonas, Acinetobacter, Burkholderia, and Stenotrophomonas

P. aeruginosa

• Oxidase: Positive

• Motility: Motile

• Key Features: Blue-green pigments, grows at 42°C

• Where you’ll see it: CF patients, burns, ICU

• Always Resistant to: Most β-lactams, aminoglycosides (some)

• First-Line: Anti-pseudomonal β-lactam + aminoglycoside

A. baumannii

• Oxidase: Negative

• Motility: Non-motile

• Key Features: Coccobacillary, survives on surfaces

• Where you’ll see it: ICU, trauma patients

• Always Resistant to: Many agents (variable)

• First-Line: Carbapenem ± aminoglycoside → Colistin if MDR

B. cepacia complex

• Oxidase: Positive

• Motility: Motile

• Key Features: Environmental, person-to-person spread

• Where you’ll see it: CF patients primarily

• Always Resistant to: Most β-lactams, colistin, aminoglycoside

• First-Line: TMP-SMX

S. maltophilia

• Oxidase: Negative

• Motility: Motile

• Key Features: Selected by broad-spectrum antibiotics

• Where you’ll see it: Post-antibiotic exposure

• Always Resistant to: β-lactams, carbapenems, colistins

• First-Line: TMP-SMX

Pseudomonas aeruginosa

• Blue-green pus = P. aeruginosa (pathognomonic!)

• CF patient with respiratory symptoms = Think P. aeruginosa exacerbation

• Hot tub exposure + folliculitis = P. aeruginosa

• NOT part of normal flora - if cultured, it means something

Acinetobacter baumannii

• ICU patient on ventilator = High risk for A. baumannii VAP

• Trauma/military wounds = "Iraqibacter"

• Survives months on surfaces = Major infection control concern

Burkholderia Species

• CF patient + lung transplant denial = B. cepacia complex

• Southeast Asia travel + pneumonia = B. pseudomallei (melioidosis)

Stenotrophomonas maltophilia

• Broad-spectrum antibiotic use = Selects for S. maltophilia

• Intrinsically resistant to everything except TMP-SMX

Efflux Pumps

pump antibiotics out (P. aeruginosa)

β-lactamases

destroy β-lactam antibiotics

Biofilms

protective matrix (especially P. aeruginosa in CF)

Low Permeability

antibiotics can't get in

Serious P. aeruginosa infections

β-lactam + aminoglycoside

MDR organisms

combine different mechanisms

Never assume coverage

always check susceptibilities!

Special Dosing Considerations

• Higher doses often needed for these organisms

• Extended infusions for β-lactams (time-dependent killing)

• Optimize aminoglycoside dosing - extended interval preferred

Monitoring Requirements and Why

• Colistin

• Aminoglycosides

• All agents

Colistin

• Serum creatinine

• Nephrotoxicity (dose limiting)

Aminoglycosides

• Peak/trough levels, creatinine

• Efficacy + nephrotoxicity

All agents

• Clinical response, repeat cultures

• Resistance development

Cystic Fibrosis Patients

• Colonization ≠ Infection - treat exacerbations, not every positive culture

• Chronic suppressive therapy - not curative

• Inhaled antibiotics - tobramycin, aztreonam, colistin

• Proper inhalation technique is critical for success

• B. cepacia = transplant complications at many centers

ICU Patients

• High risk for MDR organisms - longer stays, more antibiotic exposure

• Empiric therapy challenges - balance coverage vs. stewardship

• Contact precautions for MDR organisms

• Environmental cleaning crucial (especially Acinetobacter)

Melioidosis (B. pseudomallei)

• Two Phase Treatment

  • Intensive Phase: 10-14 days IV (ceftazidime/meropenem)

  • Eradication Phase: 3-6 months oral (TMP-SMX/doxycycline)

• Patient adherence crucial - prevents relapse

Blue-green pus

P. aeruginosa

Drug of choice for B. cepacia and S. maltophilia

TMP-SMX

Colistin nephrotoxicity

Requires serum creatinine monitoring

CF patients need combination therapy

for P. aeruginosa exacerbations

Acinetobacter survives on surfaces

Infection control nightmare

Never use colistin empirically unless…

high MDR risk