A 34-year-old woman comes to the physician complaining of fever, dysuria, and flank pain. Her temperature is 37.8 C (100 F), blood pressure is 122/78 mm Hg, and pulse is 84/min. Physical examination elicits suprapubic and costovertebral angle tenderness. Urine dipstick analysis reveals positive leukocyte esterase and nitrite. A subsequent urine culture grows colonies of motile Gram-negative rods demonstrating a green metallic sheen on eosin methylene blue (EMB) agar and hemolysis on blood agar. Which of the following is the most important bacterial factor responsible for this patient's condition?

Question

A 34-year-old woman comes to the physician complaining of fever, dysuria, and flank pain.  Her temperature is 37.8 C (100 F), blood pressure is 122/78 mm Hg, and pulse is 84/min.  Physical examination elicits suprapubic and costovertebral angle tenderness.  Urine dipstick analysis reveals positive leukocyte esterase and nitrite.  A subsequent urine culture grows colonies of motile Gram-negative rods demonstrating a green metallic sheen on eosin methylene blue (EMB) agar and hemolysis on blood agar.  Which of the following is the most important bacterial factor responsible for this patient's condition?

Quizplus · Accepted Answer

11ec160b_3877_f6e2_9249_ebe35c9369c0_MD0001_00 Escherichia coli is part of the normal bacterial flora of the intestinal tract. It is a motile, Gram-negative bacillus that is facultatively anaerobic and able to ferment both lactose and glucose. E coli grows well on blood, MacConkey, and eosin methylene blue (EMB) agar plates. EMB agar is a selective and differential medium used to isolate and identify enteric pathogens from contaminated clinical specimens. On EMB agar, organisms that ferment lactose, such as E coli, bind to dye in the agar and produce colonies that have a distinct green metallic sheen. Most strains of E coli also demonstrate beta-hemolysis on blood agar. E coli is responsible for urinary tract infections (UTIs), neonatal meningitis, and several types of gastroenteritis. The virulence factors expressed by a particular strain of E coli will determine disease characteristics. Fimbriae, or pili (Type 1 fimbriae, P fimbriae, and S fimbriae), are one of the most important virulence factors expressed by E coli. They permit the adhesion of E coli to epithelial cells, uroepithelial cells, and enterocytes. E coli causes approximately 80% of all UTIs. UTIs are more common in women than men due to the female urethra being significantly shorter. E coli originates in the feces and spreads to colonize the perineal, genital, and - most importantly - the periurethral regions. During sexual intercourse or bladder catheterization, E coli can be propelled into the urethra and bladder from the colonized periurethral region. P-fimbriae (pyelonephritis-associated pili) adhesion then allows uropathogenic E coli to colonize the bladder and ureters, causing cystitis and pyelonephritis. (Choice A) E coli strains causing neonatal meningitis synthesize K1 capsular antigens. The K1 antigen is considered the major determinant of virulence among strains of E coli that cause meningitis. (Choice B) Enterotoxigenic E coli produce heat-stable (ST) and/or heat labile (LT) enterotoxins. ST activates guanylate cyclase, causing an increase in cGMP. LT activates adenylate cyclase, increasing cAMP levels. In both structure and mode of action, LT is very similar to the cholera toxin. (Choice C) The O antigen is a variable polysaccharide antigen found on the outer membrane that is used to classify Gram-negative bacteria. It is the most extracellular component of lipopolysaccharide (see Choice E). (Choice E) The lipid A component of lipopolysaccharide is similar for all enterobacteria. Lipid A causes activation of macrophages, leading to widespread release of IL-1, IL-6, and TNF-alpha, which in turn causes the signs and symptoms of septic shock. Educational objective: E coli is one of the dominant components of the normal flora in the intestinal tract of humans and animals. It causes approximately 80% of all urinary tract infections. P fimbriae are the most important virulence factor that uropathogenic E coli express. Without P fimbriae, E coli would not be able to bind to uroepithelial cells and infect the bladder, ureters, and kidneys. Instead, the bacteria would simply be washed away during urination. __________ References: Origins and virulence mechanisms of uropathogenic Escherichia coli. (http://www.ncbi.nlm.nih.gov/pubmed/18482721)

A 34-Year-Old Woman Comes to the Physician Complaining of Fever