Overview of glucose nonfermenters

These are gram-negative organisms that do not ferment glucose in the lab.

These are also technically ‘nonfermentors’, but will be discussed elsewhere: • Legionella • Moraxella • Bordetella | • Acidovorax • Achromobacter • Alcaligenes • Brevundimonas • Comamonas • Delftia • Elizabethkingia • Methylobacterium • Ochrobactrum • Oligella • Pandoraea • Psychrobacter • Ralstonia • Roseomonas • Shewanella • Sphingobacterium |

Pseudomonas

Main species to know about are:

-       aeruginosa -       putida -       fluorescens

| Site | -       Wet environment -       Waterways -       Built environment: taps, water systems (Esp if Cold water T >20) | | --- | --- | | Risk Factors | -       ITU admission -       Abnormal lung (CF, Bronchiectasis, COPD) -       UTI | | Pathogenic mechanisms | -       Exotoxin A/S -       Endotoxin -       Cytotoxin: o   Cytotoxin o   Haemolysin o   Phospholipase o   Protease -       Fimbriae | | Clinical syndromes | Common clinical diseases: -       UTI -       HAP/VAP -       SSI -       BSI -       Otitis externa -       Hot Tub fasciculitis -       Eye infections -       Rare: Discitis, IE, Septic arthritis (esp. PJI) |

Lab diagnostics

• Bug:
  • Aerobic
  • Nonsporing
  • Motile (1+ polar flagella)
  • No capsule
  • Straight/slightly curved rod
• Agar: Blood, Choc, Maconkey
• Colony:
  • Smell: ‘fruity’ (grapes; due to aminoacetophenone), cut grass
  • Irregular white/yellow/green colonies, metallic edge. Can be surrounded by blue-green pigment; fluoresce.
    • NB: Resp samples: mucoid (slow to Oxidase, may require further ID)
• Species ID
  • Biochemical: Pseudomonad = Ox+ Cat+ glucose nonferm GNB
  • MALDI (Mis-IDs: Ralstonia, Sphingobacterium [No Ref data])
  • 16S RNA PCR (E.g. in CF patient sputum [allows earlier than Cx])

SMI Flowchart for Nonfermentor identification

Oxidase results for nonfermentors

Treatment

1. Beta-lactams:
   • Pen: PipTaz, Ticarcillin/clavulanate
   • Ceph: Ceftaz, Cefepime
   • Carba: Mero, Imi/c, Dori
   • Aztreonam
2. Quinolones: Cipro, Levo
3. Aminoglycosides
   • Tobra, Amik (urine)
     • EUCAST: Breacketed breakpoints; OK for use in urine, caution in systemic infection
     • CLSI: Tobramycin in systemic infections, Amikacin in urine only
   • Not Gent: Old breakpoint bisected WT population
4. OTHER:
   • Fosfo: In urine, as long as MIC <ECOFF (256)
   • Doxy: In urine, as urine Cmax (300) exceeds MIC (150) (cf. plasma Cmax=4)

We can also use the new BL/BLIs:

• Ceftolozane/tazobactam