Overview of glucose nonfermenters

Stenotrophomonas

• Type species is S. maltophilia
  • 1943: found in pleural fluid; named Bacterium bookeri,
  • 1961: renamed Pseudomonas maltophilia,
  • eventually became the type species of Stenotrophomonas in 1993
• 14 other Steno spp – all causing OI but otherwise env pathogens

Epidemiology:

• Commonest carbapenem-resistant, G-neg that causes bacteraemia
• 4th commonest nonfermentor in hospital isolates
• 70% cultured alongside other orgs (Pseudomonas, Enterobacterales, S.aureus)

| Site | - Environment (NB: low virulence)

• Water
• Soil
• Captive snake microbiome! | | --- | --- | | Risk Factors | - Immunocompromise o #1: Haem malignancy (Causes BSI, haemorrhagic LRTI)
• #2: Chronic Resp disease (COPD, CF [1/3 colonised; assc with progressive deterioration], etc)
• Hospital environment: o ICU o Carbapenem use o Lines/catheters | | Pathogenic mechanisms | - Biofilm, esp on abiotic surfaces (IV line, Vents etc) + Abnormal lung/trachea o Multispecies films with Pseudomonas: o “Steno substantially influences the architecture of P. aeruginosa structures, causing development of extended filaments. These changes arise due to diffusible signalling factor encoded by Steno.”
• Virulence factors o Inflammatory outer membrane vesicles | | Clinical syndromes | - HAP/VAP (Mortality 25-75%)
• IV line infection —> BSI (Mortality 20-60%)
• UTI
• Infections in eye, CNS, liver, bone, soft tissue, GIT

NB: 70% infections are polymicrobial |

Lab diagnostics

• Bug:
  • Aerobic
  • Straight/slightly curved rod
  • Nonsporing
  • Motile NLF:
    • Cat+
    • Ox-
    • DNAse+
• Agar:
  • Standard blood agar
  • Colistin-media (DDx: B.cepacia)
  • Imi-R = suspect Steno
• Colony:
  • Green-yellow
  • Some: slight beta-haemolysis
  • Ammonia smell
• Species ID
  • Biochemical: Cat+, Ox-, Imi-R —> think Steno
  • MALDI
  • 16S: Poor at telling between:
    • Steno
    • ABC
    • Achromobacter
    • Some Pseudo spp (fluorescens, Jessenii)
  • MLST: Mostly for epidemiology work/outbreak Ix.

Antimicrobial susceptibility testing in Steno (is difficult)

• EUCAST: Have only issued breakpoints for Co-trimoxazole and Cefiderocol (sort of).
• USA:
  • FDA breakpoints: “FDA recognizes only ceftazidime breakpoints…This is problematic because the FDA has required [AST] systems to use FDA breakpoints…since 2009…Laboratories, therefore, are faced with two options for conducting S. maltophilia cAST: (i) use commercial cAST systems approved prior to 2009 when CLSI breakpoints were allowed on commercial systems or (ii) perform off-label cAST on systems approved after 2009.”
    • Also regarding real-world effectiveness of Ceftazidime: given most Steno infections are polymicrobial, was the Ceftazidime just treating the other gram-negatives (e.g. Pseudomonas)?
  • CLSI: Agreement with different AST systems is varied:

From Kunz Coyne et al. Percentages are with reference to the gold-standard, broth microdilution