Microbiology Cheat Sheet
Uti: Specimen Before Count
UTI specimen before count for NEET-PG: uropathogenic E. coli P fimbriae, S. saprophyticus, Proteus struvite stones, Kass criteria, and asymptomatic bacteriuria.
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Uti: Specimen Before Count
UTI specimen before count for NEET-PG: uropathogenic E. coli P fimbriae, S. saprophyticus, Proteus struvite stones, Kass criteria, and asymptomatic bacteriuria.
This topic covers the etiopathogenesis, specimen collection, and laboratory diagnosis of urinary tract infections, emphasising correct specimen collection before colony count interpretation.
High-yield lines
- Escherichia coli causes about 80 to 90 percent of community-acquired uncomplicated UTIs in young women.
- P fimbriae of uropathogenic E. coli bind the P blood group antigen on uroepithelium and are the adhesin most strongly associated with pyelonephritis.
- Type 1 fimbriae bind mannose residues and are important in cystitis and early bladder colonisation.
- Staphylococcus saprophyticus is the second most common cause of cystitis in young sexually active women and is novobiocin-resistant.
- Proteus mirabilis produces urease that alkalinises urine and promotes struvite stone formation, with swarming motility on blood agar as a culture clue.
- Midstream clean-catch urine with 10 to the fifth CFU per millilitre of a single uropathogen is the traditional Kass criterion for significant bacteriuria.
- In symptomatic women, colony counts as low as 10 to the third CFU per millilitre may be significant.
- Suprapubic aspirate is normally sterile, so any growth of a uropathogen is significant.
- Catheter specimens must be aspirated from the sampling port or a newly placed catheter, and drainage bag urine is never acceptable for culture.
- Asymptomatic bacteriuria should not be treated except in pregnancy and before urological procedures with anticipated mucosal bleeding.
- Urine specimens must reach the laboratory within 2 hours or be refrigerated or preserved with boric acid to prevent falsely elevated counts.
- Pyuria with at least 10 white cells per cubic millimetre supports UTI, and sterile pyuria suggests TB, chlamydial or gonococcal urethritis, or stones.
- The nitrite dipstick detects nitrate-reducing Enterobacterales but is falsely negative with enterococci, staphylococci, and Pseudomonas.
- Mixed growth with squamous epithelial cells suggests contamination and warrants a repeat specimen.
Mapped competency codes
- MI7.1
- MI7.3
Continue into the full chapter
This summary maps to MI7-genitourinary-and-sexually-transmitted-infections.
Frequently Asked Questions
Which E. coli adhesin is most associated with pyelonephritis?
P fimbriae, which bind the P blood group antigen on uroepithelial cells.
When is catheter urine acceptable for culture?
Only when aspirated from the sampling port or a newly placed catheter; drainage bag urine is never acceptable.
When should asymptomatic bacteriuria be treated?
Only in pregnancy and before urological procedures with anticipated mucosal bleeding.
What does sterile pyuria suggest?
Tuberculosis, partially treated UTI, urolithiasis, interstitial nephritis, or chlamydial and gonococcal urethritis.
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