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10 Cards in this Set
- Front
- Back
visual urine sample
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Look at urine, if cloudy more likely to have lots of bacteria
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gram stain
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+ 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 |
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dipstick/urine strips
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+ 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 |
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Interpret a urine colony count and determine when it is clinically significant
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* 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 |
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Discuss the reasons for artificially low and high urine colony counts
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* 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) |
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Explain the principles of aerobic GNR ID
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* 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 |
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MIC and MBC (min bactericidal concentration)
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* 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 |
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Disk Diffusion test
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* 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 |
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E Test
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* 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 |
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Serum Antimicrobial Levels
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* 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 |