Microbiology-UTI Flashcards
Cystitis
Bacterial infection in the bladder
Pyelonephritis
Renal infection ascending from bladder or spread hematogenously
A patient has a history of multiple UTIs. She has been unable to resolve her current infection with antibiotics. Why might this be?
Treatment of multiple UTIs with antibiotics creates a normal flora that is very resistant to antibiotic therapy.
What innate defenses exist against UTIs?
Low urine pH (5.5), Tamm-Horsfall protein, Lactoferrin (sequesters Fe from bacteria), Lipocalin, defensins and unidirectional flow of urine.
What puts people at risk for UTIs?
Dehydration, urinary tract obstruction, sexual intercourse, catheterization, vesicoureteral reflux of urine and being female.
A 21 year old female presents with dysuria (inflammation), increased urinary frequency and suprapubic pain. What normal flora bacteria could be causing her symptoms if she is not sexually active?
Bacterial vaginosis…causes uncomplicated cystitis
A 77 year old female presents with right flank pain, a fever of 101, nausea, vomiting and chills. Labs reveal increased CRP levels. What type of UTI might this patient have and why do you need to control it immediately?
Pyelonephritis. 30% of these cases make it to the kidney, get into the blood stream and patients become bacteremic.
Who are the most common offenders in uncomplicated UTI?
E. coli and staph saprophyticus.
What type of bacteria makes up 90% of uncomplicated UTI cases?
Gram negative, oxidase negative enterobacteriaceae of our normal intestinal flora (to include E. coli, Proteus mirabilis, Enterococci and Klebsiella p.)
What bacteria makes up 10% of uncomplicated UTI cases?
Gram positive, beta-hemolytic, catalase positive, coagulase negative and novobiocin resistant staph saprophyticus
Most E. coli bacterium of our normal flora do not have pathogenic effects. What virulence factors are present in E. coli that cause UTIs?
Factors carried on pathogenicity islands (PAIs): Type I fimbriae (aid in adherence to the uroepithelium), P pili (aid in adherence to the uroepithelium), hemolysin (lyses uroepithelial cells) and cytonecrotizing factor (increases PMN response at infection site).
Why does a patient with a UTI from E. coli sometimes present with hematuria?
E. coli’s virulence factor, hemolysin, lyses uroepithelial cells
A patient comes to see you with her third UTI in the past year. What factors may make her more susceptible than others to recurrent UTIs?
Perineal bacterial environment, bacterial strain characteristics, and genetics.
What is complicated UTI?
UTI secondary to metabolic disorders, anatomic impairment or unusual pathogens (yeast).
How might a patient with a catheter-associated UTI present differently than someone with an uncomplicated UTI?
Symptoms may be nonspecific such as leukocytosis (elevated WBC) or pyuria (pus in urine)
What organisms are associated with complicated and catheter-associated UTIs?
Enterobacteriaceae (Proteus mirabilis, E. coli, Klebsiella p.), pseudomonas (especially catheter associated), staph aureus, staph saprophyticus, enterococcus and yeast.
Why are catheters so good at causing UTIs?
Biofilm producing organisms colonize on them (S. epidermidis, S. aureus and enterococcus)
A 66 year old man presents with a fever, dysuria and pyuria. He had a kidney stone last week. He has a urine catheter in place. Culture of a urine sample is shown below. What virulence factors about this organism make it so good at causing UTIs?
Proteus mirabilis forms the swirling pattern on plates and is common in patients with catheters. It has flagella that make it very motile and able to firmly adhere to the uroepithelium. It also makes urease, which dissociates urea, lowers the pH of urine, allowing it to survive and produces kidney stones on the side.
Why similar characteristic of staph saprophyticus and proteus mirabilis allow them to survive in the urinary tract?
Production of the enzyme urease.
A 66 year old man presents with a fever, dysuria and pyuria. He had a kidney stone last week. He has a urine catheter in place. Culture reveals a gram-negative rod, oxidase positive, non-lactose fermenter of MacConkey agar. Urine culture is shown below. What virulence factors about this organism allow it to cause UTIs?
Pseudomonas aeruginosa produces the pyoverdin (sticky green pigment) seen on culture. It has flagella, pili, an alginate capsule and produces tissue-damaging cytotoxins (LPS, hemolysins and pyocyanin)
You have complicated/catheter-related UTI and the doctor sees gram-positive rods. What characteristics will help the lab differentiate the most likely infecting agents?
1) Staph epidermidis (coagulase negative), doesn’t do a ton of damage. 2) Staph aureus (coagulase positive) 3) Enterococcus (non-hemolytic, hydrolyzes bile and tolerant to growth in 6.5% NaCl).
A 66 year old man presents with a fever, dysuria and pyuria. He had a kidney stone last week. He has a urine catheter in place. Culture reveals a gram-positive, catalase positive rod. What virulence factors about this organism allow it to cause UTIs?
Defense against phagocytes (Protein A, catalase converts fibrinogen to fibrin, leukocidin), techoic acid (TSS), capsulated, hemolysin and sphingomyelinase.
What complicated-UTI causing bacteria is becoming more and more resistant to vancomycin?
Enterococcus
What is indicated if you see urinary casts in a lab test for a UTI?
Urinary casts indicate an upper urinary tract infection because they are proteins secreted from the kidney.
What laboratory limits define uncomplicated UTIs? Complicated UTIs? Catheter-associated UTIs?
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Why is suprapubic aspiration of urine diagnostic of a UTI if you find a single bacteria in the sample?
The sample is straight from the bladder and should be sterile.
What drugs are used to treat UTIs?
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