Urinary Tract Infections (UTIs)

1
Urinary Tract Infections (UTIs)

• Microbiological Investigation

2
What are UTIs?

• A significant bacteriuria in the presence of
  symptoms
• Bacteria most often of faecal origin
• Common causes of acute UTIs
• 50-70 E. coli strains
• 5-15 Klebsiella pneumoniae
• 5-15 Enterobacteriaceae or enterococci

3
Genito-Urinary tract
4
Presentation of UTIs

• Urethritis
• The inflammation and infection is limited to the
  urethra
• It is usually a sexually transmitted disease.
• Present in men and women
• Cystitis
• Irritation of the lower urinary tract mucosa
  (i.e. bladder)
• Dysuria (painful urination)
• Urgency frequency but small
• Suprapubic tenderness
• Pyuria
• Haemorrhagic cystitis
• Large quantities of visible blood in the urine
• Caused by an infection (bacterial or viral)
• Irritation when voiding
• Pyelonephritis
• Kidney infection from lower UTI infection
• Complications sepsis, septic shock and death

5
Epidemiology

• Second only to respiratory infections (gt6 million
  visits to doctors per year USA)
• 2 incidence in preschool children 2 - 10 times
  more common in females
• 5 of school-aged females but rare in
  school-aged males
• Large majority of adult cases are females - 301
• Forty percent of all females have at least one
  episode of a UTI at some time in their lives.

6
Epidemiology (2)

• Women generally don't have many problems with
  UTI's until they become sexually active.
• Postmenopausal
• bladder or uterine prolapse
• loss of estrogen that causes a change in the
  vaginal flora
• loss of lactobacilli in the vaginal flora which
  results in periurethral colonisation
• Males experience a rapid increase in the
  incidence UTI's sometime in their 50s - benign
  prostatic hypertrophy.

7
Predisposing factors

• Sexual activity in females (7590)
• Abnormality of the UT that obstructs or slows the
  flow of urine (i.e. kidney stone)
• Elderly males prostatic hypertrophy
• Pregnancy
• Catheterisation
• Surgery, e.g. prostatectomy
• Diabetes mellitus

8
Predisposing factors (2)

• Immunosuppressed patients
• Congenital abnormalities in infants that
  sometimes require surgery, e.g. vesico-uretic
  reflux
• Women who use the diaphragm and spermicides
• Patients with a neurogenic bladder or bladder
  diverticulum

9
Human kidney

• Infection due to ascent from the lower urinary
  tract pyelonephritis
• Factor leading to retrograde flow of the urine to
  the kidney/pyelonephritis
• Cystitis due to a strain of E coli (mannose
  resistant pili bind epithelial/RBC)
• Internalisation of E coli in the proximal tubular
  epithelial cells
• Reflux of urine to the kidney - incomplete
  development of ureterovesical valves.
• Physiological malfunctions e.g. poor emptying
  of the bladder
• Urethral catheters bacteria conduit
• Urinary tract stones - a place in which bacteria
  can escape antibiotics and cause further
  infections. Bacteria can cause stone formation.

10
Human kidney (2)

• Kidney damage from
• the pathogen producing polysaccharide, which
  inhibits phagocytosis
• alpha haemolysin and cytotoxic necrotising factor
  1, causes tissue damage directly
• endotoxin that contributes to inflammation

11
Types of UTI

• Non- sexually transmitted!
• Cystitis inflammation of bladder wall
  accompanied by dysuria and frequency
• Cystitis is much the commonest, discomforting but
  not serious
• Upper tract infections, e.g. pyelonephritis, are
  much more serious
• Accompanied by fever and risk of complications

12
Causative agents mainly faecal bacteria

• Community -acquired
• Escherichia coli
• Proteus mirabilis
• Klebsiella pneumoniae
• Enterococcus faecalis
• Staphylococcus species

• Hospital acquired
• Pseudomonas aeruginosa
• Candida albicans
• AND (community acquired)Mycobacterium
  tuberculosis (renal TB will be a sterile
  pyuria

13
Investigation the specimen

• Mid-stream Urine (MSU) is the specimen of choice
• Suprapubic urine
• Catheter urine
• In all cases, urine must be examined immediately
  or stored at 4oC
• Contamination of urine is a big problem!!
• Should also determine the site of infection

14
Diagnosis

• Urine culture yielding greater than 100,000
  colony-forming units (105 CFU) per ml
  significant bacteriuria.
• However, 30 or more of symptomatic women have
  CFU counts below this level
• Therefore, urine cultures are no longer advocated
  pyuria (slide/dipstick)
• Leukocyte esterase test - sensitivity of 75-90
  pyuria associated UTI
• Dipstick test for nitrite a surrogate marker for
  bacteriuria - not all uropathogens reduce
  nitrates to nitrite
• Gram stains of urine can be used to detect
  bacteriuria - time-consuming and has low
  sensitivity

15
Standard procedures

• Investigation of UTI involves the detection of
  bacteriuria together with evidence of an
  inflammatory response
• Microscopy for pyuria and haematuria (can also
  reveal other structures, e.g. crystals, other
  cells, casts)
• Culture for detection of bacteria
• Sensitivity testing to advise on antibiotic
  treatment

16
Microscopy

• Not always performed as it is time consuming
• The finding of a rise in WBCs (pyuria) should be
  linked to a bacteriuria
• May also see RBCs (haematuria) this is
  potentially an important finding
• Microtitre plate and an inverted microscope
  enables many urines to be simply screened

17
White cells in urine

• In normal state, there is a continuous secretion
  of WBCs into urine
• In a UTI caused by bacteria, neutrophils may be
  secreted in large numbers
• Labs may report gt200/µl (gt200 x 103/ml) and will
  suggest this as significant pyuria
• Lower numbers lt 103/ml are regarded as not
  significant

18
Automation

• Looking for particles suspended in a fluid
• In the same way platelets and white cells can be
  automatically estimated in blood, so, too, can
  urine be analysed for its cellular content
• Faster, less labour intensive and reliable
• For example, flow cytometry

19
Culture procedure

• Cystitis is usually caused by a single species of
  bacterium present at gt105/ml
• Standard loopful of urine is streaked onto a
  selective medium, e.g. CLED
• Typically 1µl
• Incubate overnight and count the colonies
• If a genuine UTI, should see gt100 colonies this
  gt100 bacteria/µl or gt105/ml

20
Culture interpretation

• gt105/ml of a single species strongly suggests a
  UTI
• 104-105/ml of a single species is equivocal
  needs repeat specimen for testing
• lt104/ml is regarded as no significant growth
• gt1 species in any numbers suggests contamination
• Catheter and suprapubic urines should be
  interpreted differently

21
Sensitivity testing

• Clinical isolates are tested against antibiotics
  that
• a) are filtered by kidneys
• b) are usually effective against common
  agents
• Since UTIs are common, drugs should be cheap!
• Typical course of treatment 5-7 days orally,
  resulting in sterile urine
• Nitrofurantoin, nalidixic acid, trimethoprim,
  gentamicin, ampicillin, cephalosporins

22
Sensitivity testing (2)

• Nitrofurantoin - rapid reduction of
  nitrofurantoin inside the bacterial cell
  bacterial DNA damage
• Nalidixic acid - a synthetic quinolone antibiotic
  that inhibits the topoisomerase II ligase leading
  to DNA fragmentation
• Trimethoprim - dihydrofolate reductase inhibitor
  (inhibits thymadine production)
• Gentamicin - inhibits 30S ribosomal subunit
• Ampicillin - cell wall synthesis
• Cephalosporins - cell wall synthesis

23
Antibiotic sensitivities
24
Therapy and Prevention

• Clinical manifestations determine the initial
  step in therapy
• Afebrile UTI patients outpatient
• UTI patients experiencing high fever
  hospitalised
• General guidelines
• Cystitis and/or urethritis treated for three days
  with norfloxacin or ciprofloxacin.
• Pyelonephritis is more difficult to cure, can
  reoccur (i.e., treatment failure or reinfection)
• Three day therapy is inappropriate
• Intravenous antibiotics until fever breaks -gt
  oral antibiotic for 14 days.
• Culturing as a follow-up to insure treatment
  success.
• Longer course for pregnant/diabetic women

25
Therapy and Prevention (2)

• If the patient has urinary tract infections urge
  them to
• Maintain a high fluid intake
• Drink cranberry juice (tannins)
• Empty their bladder as soon as they feel the urge
• Take medications prescribed by the doctor exactly
  as instructed

26
Therapy and Prevention (3)

• 12 million urine analyses
• Cases caused by E. coli resistant to
  ciprofloxacin grew five-fold, from 3 to 17.1 of
  cases.
• E. coli resistant to trimethoprim-sulfame-thoxazol
  e - 17.9 to 24.2
• The two of the most commonly prescribed
  antibiotics used to treat UTIs.
• When they are not effective, doctors must turn to
  more toxic drugs, and the more those drugs are
  used, the less effective they in turn become.

27
Therapy and Prevention (4)