- A 22-year-old woman presents with frequency and dysuria. She is afebrile and well. You prescribe trimethoprim.
Which factor most justifies this choice over a broader-spectrum agent like ciprofloxacin?
Ciprofloxacin is unavailable in general practice
Trimethoprim is cheaper and more convenient
Narrow-spectrum antibiotics reduce collateral damage
Ciprofloxacin has poor urinary penetration
Trimethoprim covers a wider range of bacteria
🧠 Explanation: In an uncomplicated, low-risk case, a narrow agent like trimethoprim is appropriate because it’s targeted and avoids fostering resistance — even if some E. coli are resistant, treatment failure is usually low risk.
- A 32-year-old woman is diagnosed with acute pyelonephritis. You begin IV antibiotics. She asks why she can’t go home with tablets.
Which rationale best supports the use of IV therapy in this case?
IV antibiotics are always more effective
All oral options are contraindicated in pyelonephritis
Oral antibiotics require longer duration
IV delivery ensures high renal tissue levels early in illness
IV antibiotics avoid potential drug interactions
🧠 Explanation: Pyelonephritis involves renal tissue. If the patient is systemically unwell, IV therapy ensures fast, reliable delivery of adequate concentrations — crucial in preventing complications.
- You’re reviewing a urine culture from a patient with persistent dysuria. The dipstick had leukocytes but no nitrites. The culture is sterile.
Which explanation best accounts for this finding?
The patient drank too much water
The organism doesn't convert nitrates
The dipstick was contaminated
The sample was stored incorrectly
The patient has diabetic ketoacidosis
🧠 Explanation: Some uropathogens (e.g. Enterococcus, Staphylococcus saprophyticus) don’t reduce nitrates — leading to a false negative nitrite test. Sterile pyuria should prompt consideration of non-infectious causes or fastidious organisms.
- A 66-year-old man is being treated with IV gentamicin for pyelonephritis. On day 3, his creatinine begins to rise.
Which principle best explains this finding?
Gentamicin causes direct damage to the distal nephron
The infection has spread to the liver, reducing renal clearance
Volume overload has reduced glomerular filtration
Gentamicin accumulates in renal tubules and impairs function
Rising creatinine is unrelated to antibiotic choice
🧠 Explanation: Gentamicin is nephrotoxic due to accumulation in proximal tubule cells, where it interferes with mitochondrial function and reabsorption processes. This causes acute tubular injury — often subtle at first, but significant with continued exposure, especially in dehydration or baseline renal impairment. .
- A 30-year-old woman presents with frequency, urgency, and suprapubic pain. Urinalysis shows leukocytes and nitrites. You suspect infection with Escherichia coli.
Which feature of this organism most contributes to symptom development?
Toxin-mediated cell lysis in the bladder wall
Resistance to acidic urine
Ability to produce urease
Adhesion to uroepithelial cells via fimbriae
Anaerobic metabolism
🧠 Explanation: E. coli expresses type 1 and P fimbriae that help it cling to the bladder and ureter walls. This local adhesion triggers an inflammatory response, (via IL-6 and IL-8), leading to classic symptoms like urgency, dysuria, and suprapubic pain. The body senses invasion — even without systemic signs — and mobilises an innate response.
- A patient with pyelonephritis has a temperature of 39.2°C, flank pain, and vomiting. Urine culture later confirms E. coli.
Which pathophysiological process best explains the patient’s fever and systemic symptoms?
Bacterial overgrowth in the bladder
Increased urine osmolarity
Endotoxin release from Gram-negative bacteria
Activation of central baroreceptors
Ureteric inflammation blocking urination
🧠 Explanation: LPS from Gram-negative bacteria triggers cytokine release (IL-1, TNF-α), resetting the hypothalamic temperature and causing systemic signs like fever and malaise.
- A 28-year-old woman with recurrent UTIs is found to have a congenital ureteric abnormality causing vesicoureteric reflux.
How does this condition increase the risk of pyelonephritis?
It dilutes urinary antimicrobial proteins
It inhibits bladder emptying through pain
It allows retrograde flow of urine into the kidneys
It alters renal sodium handling
It increases urine alkalinity, favouring bacterial growth
🧠 Explanation: Vesicoureteric reflux allows bacteria from the bladder to ascend to renal tissue, bypassing normal protective mechanisms and increasing infection and scarring risk.
- A 25-year-old woman with no comorbidities presents with dysuria and suprapubic discomfort. She is diagnosed with cystitis and prescribed nitrofurantoin.
Why is nitrofurantoin a poor choice in suspected pyelonephritis?
It causes vasoconstriction in renal arteries
It concentrates poorly in renal parenchyma
It is inactivated by alkaline urine
It is rapidly metabolised by the liver
It has no Gram-negative activity
🧠 Explanation: Nitrofurantoin reaches high concentrations in the bladder but does not penetrate renal tissue adequately, so it’s ineffective for treating upper tract infections like pyelonephritis.
- A 32-year-old woman presents with pyelonephritis and vomiting. She is hypotensive and tachycardic. IV fluids and antibiotics are commenced.
Which physiological mechanism most contributes to her risk of acute kidney injury (AKI)?
Renal vasodilation increases urine sodium loss
Low circulating volume impairs glomerular perfusion
Bacteria directly damage glomerular membranes
Fever increases renal metabolic demand
Endotoxins stimulate excess ADH release
🧠 Explanation: Sepsis reduces effective circulating volume, impairing renal perfusion and triggering pre-renal AKI, particularly if NSAIDs or nephrotoxins are present.
- Which of the following is considered a primary defence mechanism that protects the urinary tract from ascending infections?
Uroepithelial IgG secretion
Low urinary sodium levels
Regular voiding and unidirectional flow
Anaerobic urine environment
High osmolality of renal filtrate
🧠 Explanation: Mechanical flushing through urination limits bacterial adherence and prevents ascension. Reflux or catheterisation disrupts this defence.
- A 72-year-old woman with poorly controlled type 2 diabetes presents with fever and flank pain.
Which feature of diabetes best increases her vulnerability to pyelonephritis?
Frequent urination due to osmotic diuresis
Reduced renal perfusion from hypertension
Hyperglycaemia impairs neutrophil function
Increased glomerular filtration rate
Enhanced mucosal immunity
🧠 Explanation: Hyperglycaemia disrupts neutrophil chemotaxis and phagocytosis, impairing innate defences. This increases both the risk and severity of infections, including UTIs.
- A 29-year-old pregnant woman presents with asymptomatic bacteriuria on antenatal screening.
Why is treatment of bacteriuria important in pregnancy, even without symptoms?
Because antibiotics prevent pre-eclampsia
To avoid neonatal hypoglycaemia
Because hormonal changes mask symptoms
To reduce the risk of ascending infection and preterm labour
Because the bacteria are usually antibiotic-resistant
🧠 Explanation: Pregnancy predisposes to UTI due to urinary stasis and anatomical changes. Untreated asymptomatic bacteriuria increases risk of pyelonephritis and poor pregnancy outcomes.
A 12-question quiz on urinary tract infections and pyelonephritis, focusing on microbiology, pathophysiology, antibiotic choice, and host defences.
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