67. Non-fermentative Gram-negative bacteria: genera Acinetobacter, Stenotrophomonas & Burkhold
Covers three non-fermentative Gram-negative genera, Acinetobacter, Stenotrophomonas and Burkholderia, starting with a comparison table of their Gram stain, shape, motility, oxidase, habitat and special traits. It then goes through each organism's epidemiology, the infections it causes, laboratory diagnosis and treatment, with Burkholderia pseudomallei and B. cepacia treated separately. Two further comparison tables set out lab tests and a summary of first-line drugs with resistance concerns.
Topic 67 of 113 in the MU Sofia syllabus for Microbiology (Dental Medicine, Year 2). The free AceMed note covers it in 7 sections, about 229 words (3 min of reading), with 15 flashcards.
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Non-fermentative Gram-negative bacteria: Genera Acinetobacter, Stenotrophomonas & Burkholderia
General Features
Acinetobacter baumannii
Stenotrophomonas maltophilia
Burkholderia
Lab Diagnosis
Summary of Treatments
Acinetobacter baumannii
Epidemiology & Transmission:
Ubiquitous: hospital surfaces, soil, water, even dry environments.
Transmitted via hospital equipment, hands of healthcare workers, and invasive devices (catheters, ventilators).
Diseases:
Nosocomial pneumonia (esp. ventilator-associated)
UTIs
Wound infections (trauma/burn)
Sepsis and meningitis (rare but severe)
Diagnosis:
Gram stain: short, plump G(–) coccobacilli in pairs.
Culture: grows on blood and MacConkey agar.
Biochem: oxidase variable, non-fermentative.
Treatment:
Highly multidrug resistant; often susceptible only to colistin or tigecycline.
Carbapenem-resistant A. baumannii (CRAB) is a critical concern.
Stenotrophomonas maltophilia
Epidemiology:
Common in moist hospital areas (catheters, disinfectants).
Seen in immunocompromised patients on broad-spectrum antibiotics.
Virulence:
Not very aggressive → primary virulence is extreme antibiotic resistance.
Diseases:
Bacteremia, especially via contaminated IV lines
Pneumonia, especially in ventilated or neutropenic patients
Diagnosis:
Gram-negative rods, oxidase (–), slow growth on nutrient media.
Often grows on MacConkey but non-lactose fermenter.
Treatment:
Trimethoprim-sulfamethoxazole (TMP-SMX) is drug of choice.
Resistant to carbapenems and often to aminoglycosides.
Burkholderia
B. pseudomallei (agent of melioidosis)
Endemic in Southeast Asia and Northern Australia.
Found in wet soil; transmission via cuts, inhalation, or ingestion.
Pathogenesis: survives inside macrophages, leads to abscess formation and sepsis.
Diseases:
Pneumonia (necrotizing), abscesses, septicemia.
Often mimics tuberculosis.
Treatment:
Ceftazidime or meropenem, followed by prolonged oral TMP-SMX.
B. cepacia
Low virulence but dangerous in CF (cystic fibrosis) patients and immunocompromised.
Can cause UTIs, pneumonia, catheter-related infections.
Treatment:
Trimethoprim-sulfamethoxazole, some sensitivity to fluoroquinolones.
Resistant to many β-lactams and aminoglycosides.
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