1High-yield organism associations
| Organism | Classic association | The exam point |
|---|---|---|
| Streptococcus gallolyticus (bovis) | Bacteraemia, endocarditis | Strongly linked to colorectal neoplasia: colonoscopy to exclude bowel cancer. |
| Staphylococcus aureus (MSSA) | Line sepsis, IVDU, skin | Flucloxacillin, not vancomycin: beta-lactams outperform vancomycin for MSSA. |
| Listeria monocytogenes | Pregnancy, age over 50, immunocompromise; deli meats, soft cheese | Intrinsically resistant to cephalosporins: add benzylpenicillin or amoxicillin to meningitis cover. |
| Clostridioides difficile | Recent antibiotics, healthcare exposure | Oral vancomycin or fidaxomicin. IV vancomycin is not secreted into the gut and fails. |
| Salmonella spp. | Osteomyelitis in sickle cell disease | Classic pairing; also causes reactive arthritis. |
| Pasteurella multocida | Cat and dog bites | Cellulitis within 24 hours: cover with amoxicillin-clavulanate. |
| Encapsulated organisms (pneumococcus, meningococcus, Hib) | Asplenia, hyposplenism | Vaccinate and educate about overwhelming post-splenectomy sepsis; consider standby antibiotics. |
| Streptococcus pyogenes (group A) | Acute rheumatic fever | High burden in Aboriginal and Torres Strait Islander peoples; benzathine benzylpenicillin secondary prophylaxis. |
| Pseudomonas aeruginosa | Neutropenia, burns, CF, hot-tub folliculitis | Needs an anti-pseudomonal beta-lactam (piperacillin-tazobactam, ceftazidime, meropenem). |
| Enterococcus (incl. VRE) | Intra-abdominal, endocarditis, healthcare | Ampicillin if susceptible; VRE: linezolid or daptomycin. |
| Cryptococcus neoformans | HIV, immunocompromise | India ink and cryptococcal antigen; amphotericin B plus flucytosine induction; manage raised ICP. |
2Australia-only high-yield (won't be in UK or US banks)
The exam reflects Australian epidemiology and practice. These are the local infections trainees most often under-prepare for:
Melioidosis (Burkholderia pseudomallei). Tropical northern Australia (Top End, north Queensland), wet season. Risks: diabetes, hazardous alcohol use, chronic lung or kidney disease. Can lie latent for years. Intensive phase IV ceftazidime or meropenem, then prolonged oral trimethoprim-sulfamethoxazole eradication.
Q fever (Coxiella burnetii). Abattoir, farm and animal exposure (cattle, sheep, goats, kangaroos). A key cause of culture-negative endocarditis. The Q fever vaccine is available in Australia and needs pre-vaccination skin testing and serology.
Japanese encephalitis virus. Emerged in mainland south-eastern Australia in 2022 via piggeries and waterbirds. Vaccine is free through state and territory programs for people at higher risk.
Ross River and Barmah Forest viruses. Mosquito-borne; epidemic polyarthralgia with or without rash. Endemic across Australia; serology-based diagnosis.
Hendra virus. Flying fox to horse to human (Queensland, northern NSW). Rare but high mortality; notifiable.
Leptospirosis and scrub typhus. Leptospirosis: cane and banana farmers, freshwater exposure (Queensland). Scrub typhus: northern Australia, look for an eschar. Both respond to doxycycline.
3Sample questions (Physify format)
1. A 34-year-old man who injects drugs presents with fever and lumbar back pain. Blood cultures grow methicillin-susceptible Staphylococcus aureus (MSSA). He has no antibiotic allergies. Which is the most appropriate definitive therapy?
- A. Vancomycin
- B. Flucloxacillin
- C. Ceftriaxone
- D. Daptomycin
- E. Linezolid
Answer: B
B. Correct. Flucloxacillin is the agent of choice for MSSA bacteraemia, endocarditis and osteomyelitis without penicillin allergy.
A. Vancomycin is inferior to beta-lactams for MSSA and linked to worse outcomes; keep it for MRSA or severe beta-lactam allergy.
C. Ceftriaxone has anti-staphylococcal activity and is sometimes used for outpatient therapy, but a narrow-spectrum anti-staphylococcal penicillin is first line.
D. Daptomycin is for MRSA or beta-lactam intolerance; it is inactivated by pulmonary surfactant, so not for pneumonia.
E. Linezolid is bacteriostatic and kept for resistant gram-positives; not first line for MSSA bacteraemia.
2. A 68-year-old woman presents with fever, headache, neck stiffness and confusion. CSF shows a neutrophil pleocytosis, low glucose and high protein; Gram stain is pending. Which empirical regimen is most appropriate?
- A. Ceftriaxone alone
- B. Ceftriaxone plus benzylpenicillin (or amoxicillin) plus dexamethasone
- C. Vancomycin alone
- D. Benzylpenicillin alone
- E. Ceftriaxone plus aciclovir
Answer: B
B. Correct. Age over 50 (also pregnancy and immunocompromise) means adding Listeria cover with benzylpenicillin or amoxicillin. Give dexamethasone with or just before the first antibiotic dose.
A. Ceftriaxone covers pneumococcus and meningococcus but misses Listeria, which is intrinsically cephalosporin-resistant.
C. Inadequate empirical spectrum: misses gram-negatives and Listeria.
D. Does not reliably cover resistant pneumococcus and gives no gram-negative cover.
E. Aciclovir is for suspected HSV encephalitis (lymphocytic CSF, temporal features); this CSF is bacterial and the regimen still misses Listeria.
3. A 72-year-old man is diagnosed with infective endocarditis. Blood cultures grow Streptococcus gallolyticus (formerly S. bovis biotype I). In addition to treating the endocarditis, which investigation is most important?
- A. Colonoscopy
- B. CT chest
- C. Bone marrow biopsy
- D. Renal tract ultrasound
- E. Bronchoscopy
Answer: A
A. Correct. S. gallolyticus bacteraemia and endocarditis are strongly associated with colorectal neoplasia; colonoscopy is needed to exclude cancer or an advanced polyp.
B, C, D, E. None fits: the recognised link is specifically colonic, not lung, marrow or urinary tract.