A 28-year-old woman presents to the clinic with complaints of dysuria and urinary frequency for the past two days. She came today after noticing a small amount of blood in her urine. She recently returned from her honeymoon in Costa Rica. She uses topical corticosteroids for eczema on her arms. Family history is unremarkable. Vital signs are normal. Physical examination reveals suprapubic tenderness to palpation and no costovertebral angle tenderness. Urine dipstick shows positive leukocytes and nitrites, and an antibiotic is prescribed. Urine culture returns two days later and is positive for a motile gram-negative bacteria.
If this patient developed systemic infection with the most likely causative agent, which of the following is the toxic component of this causative agent?
- A) DNA
- B) Lipopolysaccharide
- C) Nitrate reductase
- D) Pili
- E) RNA
This patient has acute simple cystitis. The most common infectious agent of this disease is Escherichia coli. Unresolved infections can spread upward to the kidneys and eventually the bloodstream, where the lipopolysaccharide of E. coli can cause toxic shock syndrome.
Answer choices A: DNA, and E: RNA, are incorrect. E. coli does not use DNA or RNA to cause infection.
Answer choice C: Nitrate reductase, is incorrect because this enzyme is responsible for changing nitrates to nitrites and is a diagnostic tool to check for infection rather than a mechanism utilized by E. coli to cause infection.
Answer choice D: Pili is incorrect. This is a structure that allows for initial infection into the bladder but does not produce any harmful effects.
Key Learning Point
Lipopolysaccharide (LPS, endotoxin) is the major component of the outer membrance of gram-negative bacteria such as E. coli. LPS increases the negative charge of the cell membrane and helps stabilize the overall membrane structure. LPS is in large part responsible for the dramatic clinical manifestations of infections with pathogenic gram negative bacteria such as E. coli.
Dr. Ted O'Connell