Antibiotic Resistant Organisms Flashcards
Gram negative resistance: 4 major areas of need
- ESBL-producing Enterobacteriaceae
- MDR P. aeruginosa
- Carbapenem-resistant Enterobacteriaceae
- Metallo-beta-lactamase producers
Which Ambler class is the real concern in the future?
B
Metallo active site
No drugs even in production for this
Has NDM-1 carbapenemases (new delhi metallo-beta-lactamase-1)
What type of result can you get when you test too much for something with low prevalance?
False positives
The big 5 carbapenemases
KPC NDM VIM IMP OXA-48
Which drug did we used to be able to use to reliably treat CREs?
Colistan
But now there is increasing resistance - spread of MCR-1 gene
MRSA
Methicillin resistant staph aureus
Resistant to all beta-lactams
Usually multi-drug resistant
Nosocomial pathogen, easily transmissible
CA-MRSA
what is it, what does it cause, how to treat
Serious community-acquired infections
Necrotizing skin and soft tissue infections
Several clonal groups/PVL positive
Generally susceptible to Septra, doxycycline, and clindamycin
2 primary differences between CA and HA MRSA
- CA is more virulent
2. CA is less resistant (3 drugs to treat)
Risk factors for HA-MRSA
Prolonged hospitalization ICU care Prolonged antimicrobial therapy Surgical procedures Close proximity to colonized/infected patient Injection drug use Implanted devices
Why is MRSA so resistant?(what does it make, how does it work (2), what gene, where is the gene, why is it hard to identify the gene)
Results from the production of a novel PBP
PBP 2a has reduced affinity for beta-lactam agents, and can perform essential functions of other PBP
mecA gene: acquired, chromosomal
Strains can be homogenous (have the gene, its on, making lots of PBP) or heterogenous (1/1 million expressing the resistance) which makes it hard to identify
Detection of MRSA
Mueller Hinton Agar with 4% NaCl and 6ug/mL oxacillin
Salt to put the bug under slightly osmotic stress to induce resistance
Use Cefoxitin instead of oxa now because it better induces resistance
Use a LOT of organisms - heavy inoculum
Now use chromogenic agar with cefoxitin
Risk Factors for CA-MRSA
Younger age groups IV drug use Lower economic status MSM Crowded conditions
Factors conductive to spread of CA MRSA
Close skin to skin contact Cuts and abrasions Shared contaminated items/surfaces Poor hygiene Crowded living conditions
Clinical manifestations of CA-MRSA
Boils or draining pimples "Spider bites" or "bug bites" Sores that won't heal Red areas of skin that may feel warm to the touch Abscesses Systemic infections less common
SCC
Staphylococcal cassette chromosome
5 types
HA has 1, 2 or 3 and are multidrug resistant
CA has type 4 - don’t carry multiple resistance genes, usually only resistant to beta lactams and erythromycin
