Fm2 Small Group 2

Front 1

visual urine sample

Back 1

Look at urine, if cloudy more likely to have lots of bacteria

Front 2

gram stain

Back 2

+ Distinguishes b/n true bacteriuria and contamination
+ Presence of WBCs and RBCs makes it more likely to be UTI
+ Can determine shape (cocci or bacilli) and number of orgs present
# Smear w/1 or more orgs per oil immersion field = significant colony count

Front 3

dipstick/urine strips

Back 3

+ Leukocyte Esterase – enz produced by inflammatory cells
+ Bacterial nitrite – from bacterial metabolism
+ 85% Sensitive
+ Can get a false negative for the following reasons:
# Frequent urination – prevents build-up of adequate WBCs for positive leukocyte esterase test and bacteria may not have had enough time to convert the nitrate to nitrite.
# Too early in infection to pick up LE
# Pt may be neutropenic

Front 4

Interpret a urine colony count and determine when it is clinically significant

Back 4

* Urine when it comes out is generally sterile unless contaminated by NF at end of urethra and then may have low count
* Pts w/UTI have a count > 105 colony-forming units/mL of urine (clinically significant)
o 104 significant if urine collected via indwelling catheter
o 103 significant if collected by single (straight) catheterization
o If more than 2 orgs present at > 104 only the predominant one will be ID
+ Will report both if neither predom, which may be from poor collection, transport, or contamination
o Note: Some pts w/bacteriuria may have counts < 105 cfu/mL
* Counts b/n 104 and 105 are equivocal so generally redone

Front 5

Discuss the reasons for artificially low and high urine colony counts

Back 5

* Artificially Low
o Freqent urination
o Consumed lots of fluid
o IV hydration
o Note: Can overcome these probs by collecting first morning voided specimen bc orgs will be more concentrated
* Artificially High
o Urine sample contaminated/not collected properly
o Sample transport delay – need to be plated within 1 hr of collection or normal skin flora may grow in sample at room temp (if can’t culture right away put in fridge at 4C)

Front 6

Explain the principles of aerobic GNR ID

Back 6

* Must ID orgs if count signification
* Determine if GPC or GNR by testing for catalase, coagulase, other metabolites
* Observe colony growth on selective media to classify GNRs
o EMB used when culturing urine and can differentiate b/n lactose fermenter (dark colony) or nonlactose fermenter (colorless), E.coli makes so much acid from lactose brkdwn that get metallic green sheen
* Assess physiologic attributes – presence of bacterial enz, detection of metabolic end-products
o Carbohydrate Fermentation Tests
+ Color change if bacteria can metab carbs
o Nitrogen Utilization Tests
+ Diff bacterial grps
o Note: most of these tests req 18-24 hrs of incubation
* CA: E. coli, Proteus species, enterococci, staph
* HA: pseudomonas, Proteus, Serratia – harder to tx bc more resistant to abx

Front 7

MIC and MBC (min bactericidal concentration)

Back 7

* Broth Tube dilution – direct quantification of susceptibility
o Innoculte calibrated bacterial suspensions (105/mL) w/decreasing concentrations of abx (made by diluting highest conc.) and incubate at 37C for 18 hrs
o Examine for growth
o Measure bacteriostatic effect (MIC) = amt of drug in tube w/lowest conc. of abx and no observable growth
+ If this amount is something that can be easily achieved in pts’ serum via normal abx delivery organism is susceptible
+ Clinically we use a conc. that is 4x in vitro MIC
o MBC = lowest conc. that kills >99.9% of bacteria
+ Calculated after another 18-24 hrs and a culture
+ Typically only done if pt suspected to have meningitis, endocarditis, osteomyelitis, or infectious dz w/significantly lowered host defense
o Microdilution method – antimicrobial agents already come dilute, but process is the same and allows you to det MIC

Front 8

Disk Diffusion test

Back 8

* Kirby-Bauer Test
o Disks w/spec conc. of abx put on agar plate w/known amt of pure pathogen culture
o Incubate overnight
o Determine resistance or susceptibility based off amt of growth around disks

Front 9

E Test

Back 9

* Combination of Kirby-Bauer and Broth Tube dil (preformed on agar plate and directly quantifies susceptibility)
* E strip has MIC scale on one side and pre-set abx conc. gradient dried on other side (range of 15 2 fold dilutions)
* Place strip on plate w/bacterial culture
* Incubate overnight (strip releases abx continuously and exponentially)
* Next day see symmetrical inhibition ellipse (looks more like a tear-drop to me!)
* MIC is where edge of growth intersects strip

Front 10

Serum Antimicrobial Levels

Back 10

* Done by gas-liquid chromatography or immunoassay
* Same day results
* Only done to determine if effective level achieved in vivo or loosely monitor drugs that are associated w/higher toxicity