Acinetobacter baumannii

1. A. baumannii is listed as a "medically important microbe every doctor should know" — specifically highlighted as a key non-fermenting Gram-negative nosocomial pathogen alongside Pseudomonas aeruginosa ^[1].

2. Antimicrobial resistance lecture (GC 099) emphasises A. baumannii as a paradigm of multidrug resistance: it acquires carbapenem resistance via OXA-type and metallo-β-lactamases (NDM-1); colistin is often the last-line agent ^[3]. The concept of "pan-drug resistant" (PDR) organisms is discussed — A. baumannii is one of the organisms most likely to exhibit PDR.

3. Infection control lecture (GC 104) specifically highlights that A. baumannii survives on dry hospital surfaces for prolonged periods (up to weeks), making environmental decontamination critical during outbreaks. Contact precautions and enhanced terminal cleaning are stressed ^[4].

4. GC 106 (Practical issues in antibiotic use) reinforces that carbapenem use drives selection of carbapenem-resistant Acinetobacter — a core antibiotic stewardship teaching point ^[5]. Empirical carbapenem use in ICU without de-escalation is a commonly examined wrong practice.

5. The oxidase test is the single most important bench-top discriminator: A. baumannii (oxidase −) vs P. aeruginosa (oxidase +). This is a recurrently testable fact in MCQ format ^[1][2].

6. Immunocompromised host lecture (GC 102) lists A. baumannii among organisms causing infection in neutropenic/post-chemotherapy patients, particularly when there is prolonged hospitalisation and broad-spectrum antibiotic exposure ^[6].

• Oxidase test is king: In a vignette of a non-fermenting Gram-negative rod from an ICU patient, an oxidase-negative result should immediately shift your answer from Pseudomonas to Acinetobacter. An oxidase-positive result favours Pseudomonas, Burkholderia, or Stenotrophomonas (though Stenotrophomonas has variable oxidase).
• Gram stain confusion with Neisseria: The coccobacillary morphology can trick you. Key difference — Acinetobacter grows happily on MacConkey and is oxidase −; Neisseria meningitidis requires chocolate agar / enriched media and is oxidase +.
• Sulbactam trap: If a question asks "which β-lactamase inhibitor has direct bactericidal activity against Acinetobacter?" — the answer is sulbactam, not clavulanate or tazobactam. This is unique to Acinetobacter and is a common MCQ discriminator.
• Colonisation vs infection: Acinetobacter is frequently isolated from respiratory specimens of ventilated patients. The examiner may test whether you treat colonisation (you should not) vs true VAP (you should). Clinical correlation (fever, rising WCC, new infiltrates, purulent secretions) is essential.
• Colistin nephrotoxicity: If a question involves treatment of XDR A. baumannii and asks about adverse effects, renal toxicity (acute tubular necrosis) is the expected answer.
• Carbapenem-resistant Acinetobacter (CRAB): Now more common than carbapenem-susceptible strains in many ICU settings in Asia. Exam framing may present an antibiogram showing resistance to all tested antibiotics except colistin ± tigecycline.

No directly relevant past paper questions specifically naming or testing Acinetobacter baumannii were identified in the indexed past paper context provided. The following related stems may tangentially involve this organism:

• 2021 Fourth Summative SAQ Q12(a) ^[7]: "A 40-year-old man had bone marrow transplant for CML. He developed high fever on day 10 after conditioning... blood neutrophil count < 0.1 × 10⁹/L. List common microbes which could be found in his blood culture." — While the expected answers are E. coli, Klebsiella, Pseudomonas, coagulase-negative staphylococci, etc., A. baumannii is an acceptable nosocomial Gram-negative pathogen in this context if the patient has prolonged hospitalisation/ICU stay and prior broad-spectrum antibiotics ^[6][7].

• 2020 Fourth Summative Minicase Case 1, Section 4, Q12 ^[8]: "Name two likely microorganisms which can cause this condition" — context involves a medical device-related infection. While the specific device is not fully described in the indexed text, A. baumannii is relevant for device-associated infections (catheter-related BSI, VAP). The expected answers likely include S. aureus and S. epidermidis for device infections, but if the clinical picture involves a ventilated ICU patient, A. baumannii may be relevant.

No past paper question with an explicit Acinetobacter-focused stem was found in the indexed context.