Proteus mirabilis

1. GC 105: Proteus is listed under Enterobacterales with disease associations including UTI and abdominal infections. Key teaching point: ESBL-producing Enterobacterales → carbapenems are the antibiotic of choice ^[1]. This is a favourite MCQ distractor — students who pick ceftriaxone for ESBL Proteus lose the mark.

2. GC 210 (UTI lecture): Prophylaxis for recurrent UTI includes ciprofloxacin, septrin, trimethoprim, cephalexin, or nitrofurantoin 50 mg OD. Critical caveat: nitrofurantoin is avoided in pyelonephritis (poor renal tissue levels) and must be avoided entirely in Proteus (intrinsic resistance) ^[8]. This double-pitfall is highly examinable.

3. Gen Clerk Microbiology Summary: Proteus mirabilis and P. vulgaris both have intrinsic resistance to nitrofurantoin ^[7]. Listed alongside Morganella morganii and Providencia spp. in the "classical intrinsic resistance" table — expect this to appear as an MCQ option where nitrofurantoin is the wrong answer for a Proteus UTI.

4. Felix PY Lai notes (Medicine + Paediatrics): "Magnesium ammonium phosphate crystals occur in alkaline urine with increased NH₃ production by urease-producing organisms such as Proteus or Klebsiella, suggestive of UTI" ^[3]. This is a classic data-interpretation question — a urine R/M showing coffin-lid crystals in alkaline urine should prompt you to answer Proteus (or Klebsiella) UTI.

5. Ryan Ho Urogenital: P. mirabilis accounts for ~2% of uncomplicated UTI but is proportionally more important in complicated/nosocomial UTI ^[2]. In exam vignettes, Proteus UTI will typically be set in a patient with a catheter, structural urinary anomaly, or recurrent stone disease — not a young healthy woman with simple cystitis (that's E. coli).

6. Felix PY Lai antibiotic tables: 1st-gen cephalosporins cover E. coli, P. mirabilis, and K. pneumoniae; fluoroquinolones also cover Proteus mirabilis ^[6]. Know these spectra for the "best empirical antibiotic" MCQ format.

• Urease-positive UTI organism: Proteus vs Klebsiella vs Ureaplasma. In a stone-forming UTI vignette, Proteus is the default answer unless specifically clued otherwise. Klebsiella is urease + but less classically linked to staghorn calculi.
• Nitrofurantoin trap: Nitrofurantoin is an excellent drug for uncomplicated lower UTI by E. coli, but it is intrinsically resistant in Proteus, Morganella, and Providencia. If the stem names Proteus, nitrofurantoin is always wrong.
• Swarming on agar: If a question describes "swarming colonies" or "spreading film of growth," think Proteus immediately — this is the most classic culture description.
• Alkaline urine + crystals: Coffin-lid–shaped struvite crystals in alkaline urine = urease-producer. Calcium oxalate (envelope-shaped, acidic urine) and uric acid (rhomboid, acidic urine) are distractors.
• Secondary bacterial peritonitis: Proteus can appear in polymicrobial peritoneal culture — polymicrobial = secondary peritonitis (bowel leak), NOT spontaneous bacterial peritonitis (monomicrobial) ^[5].

No past paper questions directly examining Proteus mirabilis as the named organism or primary answer were identified in the indexed 2016–2025 Fourth Summative MCQ, SAQ, or Minicase papers. The organism may appear as a distractor option in UTI or antibiotic-choice stems; however, no specific question stem with a Proteus-focused answer could be faithfully quoted from the provided past paper context.