Pseudomonas aeruginosa

1. GC 102 (Fever after chemotherapy): Pseudomonas aeruginosa is highlighted as a hospital-acquired coloniser that establishes after broad-spectrum antibiotics suppress anaerobic normal flora. It forms biofilm on devices (vascular catheters, ETT, Foley's) that is difficult to eradicate without device removal ^[2]. This is a key concept for neutropenic fever management questions.

2. GC 052 (Fever and purulent sputum): In bronchiectasis exacerbations, Pseudomonas is specifically named as a pathogen in long-standing disease. Anti-pseudomonal antibiotics listed: piperacillin-tazobactam, ceftazidime, carbapenems (meropenem), aminoglycosides (amikacin), fluoroquinolones (levofloxacin) ^[4].

3. Senior notes (Ryan Ho Respiratory): Colonisation in respiratory specimens is common and must be clinically correlated before treating. Ciprofloxacin is better than levofloxacin for Pseudomonas. Ertapenem is the one carbapenem with NO anti-pseudomonal activity. Single agent generally suffices but dual therapy for severe infections. MRPA may need colistin, Zavicefta, Zerbaxa, or cefiderocol ^[3].

4. GC 102: During hospitalisation, Pseudomonas is introduced by hands of medical personnel and various diagnostic/therapeutic procedures — this underpins infection control questions ^[2].

5. HA guidelines (via Adrian Lui / senior notes): For hospitalised patients with chronic lung disease (bronchiectasis), use anti-pseudomonal antibiotics (e.g. piperacillin-tazobactam or cefepime) ± macrolide or doxycycline — this is distinct from standard CAP empirical therapy ^[6].

6. Felix Lai (Medicine/Paeds): Pseudomonas pneumonia is characterised by severe and progressive SOB. Risk factors: bronchiectasis, repeated Abx/steroid courses, structural lung disease including COPD, immunocompromised (neutropenia, HIV, transplant) ^[7].

• Oxidase test: Pseudomonas is oxidase +ve; Acinetobacter baumannii is oxidase −ve (both are non-fermenters, both cause nosocomial infections — oxidase is the key discriminator).
• Ertapenem trap: Students commonly list "carbapenems" as anti-pseudomonal — but ertapenem specifically lacks Pseudomonas coverage. Exam favourite wrong answer.
• ESBL E. coli vs ceftazidime-resistant Pseudomonas: The 2020 MCQ Q83 tested which is the MOST COMMON MDR organism in HK public hospitals — answer is ESBL-producing E. coli, NOT Pseudomonas ^[12].
• Colonisation vs infection: Isolating Pseudomonas from sputum in a ventilated patient does NOT automatically mean pneumonia — clinical, radiological, and biochemical correlation required.
• Ecthyma gangrenosum: Black necrotic skin lesion in a febrile neutropenic patient → think Pseudomonas bacteraemia (NOT fungal until later in course).
• Malignant otitis externa: Elderly diabetic with severe ear pain, granulation tissue in ear canal, cranial nerve palsies → Pseudomonas (not typical otitis externa pathogens).
• Anti-pseudomonal cephalosporins: Not all cephalosporins cover Pseudomonas. Ceftriaxone and cefotaxime do NOT. Ceftazidime and cefepime DO.
• Septic arthritis: In IVDU, think Pseudomonas (and S. aureus) rather than typical community pathogens ^[9].

2020 Fourth Summative MCQ Q83 ^[12]:

"Which of the following is the MOST COMMON multidrug-resistant organism in Hong Kong's public hospitals? A. Carbapenem-resistant Acinetobacter B. Ceftazidime-resistant Pseudomonas aeruginosa C. Extended-spectrum Beta-lactamases-producing Escherichia coli D. Methicillin-resistant Staphylococcus aureus"

Correct answer: C. ESBL-producing E. coli. Rationale: Despite Pseudomonas and MRSA being well-known MDR organisms, ESBL-producing E. coli is the most common MDR organism in HK public hospitals. This is a direct lecture-derived epidemiological fact. Ceftazidime-resistant Pseudomonas (option B) is a distractor — it is important but less prevalent than ESBL E. coli in HK surveillance data.

2020 Fourth Summative MCQ Q82 ^[12]:

"What is MORE LIKELY to be the microbial cause of neutropenic fever at day 10 post-chemotherapy? A. Aspergillus fumigatus B. Candida albicans C. Cytomegalovirus D. Streptococcus viridans"

Correct answer: D. Streptococcus viridans (for day 10 = early neutropenia; bacterial causes predominate). Relevance to Pseudomonas: Although Pseudomonas is not an answer option here, it is a key G−ve cause of neutropenic fever alongside E. coli ^[2][5]. Fungal causes (Aspergillus, Candida) become more important in prolonged neutropenia ( > 7–14 days without response). This question tests the timing concept from GC 102.

No other past paper questions in the indexed context directly name Pseudomonas aeruginosa in their stems.