Bacterial Resistance Mechanisms Flashcards
Natural Resistance
- Stuff that the bug naturally comes with
ex. Beta lactams target the cell wall. But if the bug doesn’t have a cell wall then that drug won’t be effective
Acquired resistance
- Acquisition of genes that encode resistance
1) Conjugation
2) Transformation
3) Translocation
Resistance to Beta Lactams
A) Natural resistance -No cell wall (atypical bugs) -Bug is impermeable to the drug B) Acquired resistance -Production of Beta lactamases -Altered penicillin binding proteins (PBP) -Decreased permeability of drug though outer membrane -Efflux pump
How is MRSA resistant
-mecA gene which alters PBP so that the drug cannot bind to the receptor
Which drug classes are least affected by beta lactamase degradation
- Cephalosporins
- Carbapenems
- Antistaphylococcal penicillins
Resistance to Aminoglycoside
1) Natural
- Anaerobes (oxygen is required for this drug to work)
2) Acquired
- Ribosome mutation preventing drug binding
- Amineglycoside modifying enzyme (AME) alters the drug so it cannot bind properly
- Impaired entry by porin mutation/ damage or loss of active transport
- Efflux pump
Resistance to Tetracyclines
1) Natural- N/A tetracyclines work against gram+ and gram- as well as anaerobes and atypicals
2) Acquired
- Active efflux (energy dependent)
- Ribosomal protection proteins (blocks binding of drug to ribosome)
- Enzymatic inactivation of the antibiotic
Drugs that inhibit 50s ribosome
- Macrolides
- Lincosamides
- Streptogramins (MLS resistance)
Resistance to Macrolids, lincosamides
- Reduced membrane permeability
- Efflux pump
- Plasmid associated erythromycin resistance
- Methylation of adenine in 23s bacterial rRNA
Example of Inducible resistance
- Methylation of adenine in 23s bacterial rRNA
- Can lead to clindamycin resistances due to macrolide exposure
- “D test” to check for this
