Clinical Microbiology Flashcards
What bug smells like grapes?
Pseudomonas aeruginosa
How does MALDI-TOF MS work?
A rapid diagnostic test. Has the largest library of organisms it can detect. By far. Matrix Assisted Laser desorption ionization time of flight mass spec) A rapid diagnostic method. Uses mass spec on Ionized ribosomal proteins to identify the pathogen. Compared against known pathogens in a library. Requires growth.
What is CAS (Commerical Automated Systems) in the micro lab?
These are automated systems that utilize a panel of metabolic reactions to identify pathogens, often combined with susceptibility testing. Vitek-2 and Microscan are commonly used systems. Requires bacterial growth/culture (takes a while, maybe days)
Name some Rapid Diagnostic Identification systems for the micro lab.
MALDI-TOF MS BioFire FilmArray PNA-FISH Lumex Verigene T2 Biosystems T2Dx
What is BioFire FilmArray?
A rapid diagnostic system. Uses PCR. Detects Virus a Bacteria. Uses different pathogen “panels” depending on sample type. 1 hour turn around. Detects mecA, vanA/vanB and KPC resistance genes in blood samples. Can accept nasal swab, stool, csf, blood.
What is PNA-FISH
Peptide nucleic acid fluorescent in situ hybridization (PNA-FISH). Direct from blood culture, results in as little as 30 minutes. Very limited pathogen identification range, most kits only test 2 or 3 species
What is Luminex Verigene?
Nucleic acid targets identified using oligonucleotides and gold nanoparticles, light scattering used for pathogen and resistance gene identification
Testing direct from culture; blood panels require Gram’s stain to determine use of gram-positive vs. gram-negative panel (AKA must have growth first). Can detect many resistance genes. 2 hour turnaround time
What is T2 Biosystems T2Dx
Another Rapid Diagnostic. Magnetic resonance used for identification. Direct identification from whole blood. T2Bacterial panel recently approved. Detects E. faecium, S. aureus, K. pneumoniae, P. aeruginosa, and E. coli.
There are 3 rapid identification systems that can detect resistance genes. Name them.
BioFire FilmArray Blood Panel
Verigene Blood Culture (G+ and G-)
Antibody titers are often used to detect which infections?
Syphillis
Coxiella burnetti (titers > 1:800 included in Duke criteria
for endocarditis)
Bartonella spp.
What are the classes of beta-lactamases?
Class A, B, C, and D
What do you know about class A beta-lactamases?
Examples include TEM and SHV. -Low-level penicillinases -Chromosomal or Plasmid -Inhibited by beta-lactamase inhibitors Also includes TEM-10, SHV-12, and CTX-M -These are ESBLs Also includes KPC and IMI -These are carbapenemases
What do you know about Class B beta-lactamases?
Includes IMP, VIM, and NDM
- Metallo-beta-lactamases
- Not currently inhibited by ANY beta-lactamase!
What about Class C beta-lactamases?
Think C for cephalosporinases.
- Includes AmpC, CMY-2
- Not inhibited by traditional beta-lactamases, but newer ones do work.
What about Class D beta-lactamases?
These are the most scary. OXA type.
- OXA-1 (oxacillinase)
- OXA-10 (ESBL)
- OXA-40 and OXA-48 (carbapenemases) (Use Avicaz)
What is blaZ
G+ orgs. PCN resistance in Staph and enterococci.
If an organism produces KPC, what do you treat with?
KPC is the most common carbapenemase (Class A beta-lacatmase).
-Avibactam and Vaborbactam have activity.
-
If an ESBL producer shows susceptibility to Pip-Tazo, can you use it?
NO! Study showed that despite susceptibility, Zosyn had far worse outcomes than merrem! Now we use carbapenems.
What are the three primary mechanisms of antibiotic resistance?
Modify the antibiotic (beta-lactamases)
Modify the target
Change the ability of drug to access site: Porin deletion or presence of eflux pumps.
What does mecA code for?
PBP2a, which confers resistance to beta-lactams and cephalosporins (except ceftaroline).
What are Monte Carlo Simulations?
Used to predict PK/PD stuff. Uses simulated patients given known distributions of PK parameters to predict the PK/PD outcomes of different dosing schemes. Often used for susceptibility breakpoint determination and identification of optimal dosing.
PD Exposure goals: Which drugs need T>MIC vs Cmax:MID vs AUC:MIC?
T>MIC = beta-lactams
Cmax:MIC = AG and FQ
AUC:MIC ratio: Everything else (Vanc, Dapto, PMX, Tetracyclines, Oxazolidinones).
When designing a dosing regimen, what percent target attainment (for a given MIC) is considered adqeuate?
Greater than 90%
PTA = percent target attainment
What defines antibiotic synergy?
greater than 2 log10 decrease in cfu when compared to the most active drug.
What defines bactericidal vs bacteriostatic?
A greater than 2 log10 decrease in cfu
Should aminoglycosides be used as monotherapy in serious infections?
No.
Do carbapenems and polymyxins show synergy?
Yes
Do beta-lactams show synergy?
Yes, the beta-lactam lets the AG get better access to site of action.
Beta-lactams + dapto synergy?
Yes, seesaw effect, resistance to dapto happens when the cell wall thickens and it provides more targets for beta-lactam
Beta-lactam + Vanco synergy?
Actually yes. Not used as commonly as dapto + beta-lactam. Also exhibits the seesaw effect. Vanc resistance often involves thickening of cell walls, increasing the target site for BL’s.
Ampicillin and Rocephin Synergy?
Yes! For enterococcal infections that are SUSCEPTIBLE to ampicillin. Ampicillin is bacteriostatic to entercocci on it’s own, but when rocephin is added, it becomes cidal. Which is interesting because ceftriaxone has no intrinsic activity against enterococci. Similar outcomes to Amp + Gent, but with fewer adverse events.
Is cefepime hydrolyzed by ampC producers?
Nope. It’s not! Cool!
