Stenotrophomonas maltophilia bacteraemia?

Microbiology:

• Gram negative
• Motile rod
• Polar multitrichous flagella

Identification:

• Lysine postive
• DNase positive
• Oxidase negative
• Pale yellow/lavender grey colonies on blood agar. Dark tan to lavender if continued incubation, especially at room temperature

Clinical Features:

• Can be recovered from any clinical site
• Opportunistic infections, nosocomial pathogen
• Commonst site of recover is the respiratory tract
• Increasing incidence in CF, haematology patients
• Selected by indiscriminate use of carbapenems
• Risk factors for death:
  • Patient in ITU
  • >40 yrs old
  • Pulmonary source of a Stenotrophomonas maltophillia isolate.

Managment:

• All isolates are inherently carbapenem resistant:
  • Resistance to carbapenems occurs either through bacterial production of β-lactamase enzymes that hydrolyze the antimicrobial agent or through porin changes in the bacterial cell wall that reduce the permeability of the drug into the organism. In some organisms, both mechanisms may be present. DNA coding for enzyme production can be passed from organism to organism via plasmids or can occur through mutation of an existing β-lactamase enzyme. Porin changes arise through mutation. Hyperexpressed SmeF is capable of functioning with additional multidrug efflux components to promote multidrug resistance in S. maltophilia.
• One interesting this is that there is nearly >90% susceptibility to septrin, an antibiotic which has no activity against P. aeruginosa, whilst S. maltophilia is resistant to "anti-pseudomonal" antibiotics.

Dosing:

****THIS IS A CONFUSING AREA, AND DEPENDS ON WHAT YOU READ*****

1. BNF: When discussing the dosing of septrin: 120mg/kg/day in 4 divided doses (PCP dose)
2. Johns Hopkins: 15-20mg/kg/day [of the TRIMETHOPRIM component] in 3 divided doses
3. Patients treated with a high daily dose of septrin (2400/480 mg), had better outcome than patients receiving lower doses^REF. This is based on "high-dose septrin: 12–15 mg/kg/day [based on the TRIMETHOPRIM component] in 3–4 doses.
4. "1920mg bd", should ONLY be used in combination therapy^REF.

In summary, this empirical guide is quite useful:

AMH.