›Burkholderia pseudomallei — Gram-negative aerobic bacillus
›Environmental saprophyte found in soil and surface water
›Hardy — survives desiccation, UV, detergents
›Tier B select agent (CDC bioterrorism classification)
›Intrinsic resistance mechanisms
›Efflux pumps — BpeAB-OprB mediating resistance to aminoglycosides and polymyxins
›Inducible chromosomal beta-lactamase (PenA)
›Outer membrane porin changes
›Infection routes
›Percutaneous inoculation through skin abrasions most common
›Inhalation during aerosol events (storms, soil disruption)
›Ingestion via contaminated water (near-drowning)
›Rare: nosocomial or laboratory exposure
›Pathogenesis
›Intracellular survival in phagocytes enables dissemination
›Actin-based motility for cell-to-cell spread
›Type 3 secretion system and type 6 secretion system virulence
›Abscess formation is hallmark
›Characteristic multi-organ abscess pattern — lung, liver, spleen, prostate, bone
›Latency and reactivation
›Organism persists intracellularly for decades
›Reactivation triggered by immunosuppression, illness, or pregnancy
›Documented reactivation up to 62 years after exposure
›Clinical syndromes
›Localised infection — skin, soft tissue, parotid gland (children)
›Pneumonia — most common presentation ~51% of cases
›Bacteremia without evident focus — poor prognosis
›Disseminated disease — multi-organ abscesses with or without bacteremia
›Neurological melioidosis — brainstem encephalitis, myelitis, cerebral abscess
›Chronic melioidosis — symptoms >= 2 months (~11% of cases)
Therapeutic Considerations
›Antibiotic strategy rationale
›Two-phase approach is standard of care
›Intensive phase eliminates organism burden
›Eradication phase clears intracellular reservoir and prevents relapse
›Duration must be individualised
›Uncomplicated pneumonia or bacteremia: 10–14 days IV then 3 months oral
›Bone, joint, CNS, or prostatic disease: 4–8 weeks IV then 6 months oral
›Relapse risk highest when eradication therapy shortened or stopped early
›Treatment response expectations
›Median fever defervescence 9 days on appropriate IV therapy
›Slow response expected — not a sign of treatment failure
›Switch therapy only with culture evidence of resistance or clinical deterioration
›Relapse rate ~6–10% even with full treatment course
›Within 10 years ~16% relapse in Thailand cohort
›Second course of standard intensive plus eradication therapy for relapse
›Resistance considerations
›Primary resistance to ceftazidime rare (< 1%)
›Secondary resistance may emerge with subtherapeutic dosing
›Meropenem retains activity against ceftazidime-resistant strains
›No fluoroquinolone or tigecycline role in standard therapy
›Moxifloxacin has limited activity — not recommended
›Surgical adjunction
›Drainage alone without antibiotics — insufficient
›Antibiotics alone without drainage for accessible collections — associated with treatment failure
›Combined medical and surgical approach standard for visceral abscesses