Bacterial Resistance Mechanisms Flashcards
Define resistance in relation to the antimicrobial treatment of bacteria
when an organism is not killed by antimicrobial presence at the site of infection
Name the two ways in which bacteria can become resistant
Inherent/Intrinsic
Acquired
What is intrinsic/inherent resistance?
All strains of a species are naturally resistant to an antibiotic
e.g. streptococci always resist aminoglycoside action
Gram negative bacteria always resist vancomycin action
What is acquired resistance?
Resistance in some strains of the species but not others
Laboratory sensitivity testing required to establish sensitivity of any culture from an individual patient
What two methods can cause acquired resistance?
Spontaneous mutation during DNA multiplication
(structure/function change - antibiotic target changes)
Resistant gene spreading from species to species
Describe two methods of bacterial gene carriage
Plasmid - extra chromosomal DNA packages
Transposon - DNA packets that insert themselves into the chromosome
Give two current forms of bacterial resistance
Beta-lactam resistance
Glycopeptide resistance
Other forms of resistance
In what two ways does beta-lactam resistance come about?
Beta-lactamase production
Penicillin binding protein (PBP) target site alteration
What is beta-lactamase?
Bacterial enzymes that inactivate beta-lactam antibiotics by cleaving the beta-lactam ring
Give examples of bacterial species that become resistant through beta-lactamase production
Staphylococcus aureus resistance to penicillin G
Many Gram negative bacteria
How is beta-lactamase resistance combatted?
Adding a beta-lactamase inhibitor to the antibiotic
(e.g. co-amoxiclav = amoxicillin + clavulanic acid)
Producing a beta-lactamase resistant antibiotic by modifying the side chain
(e.g. flucloxacillin - modified penicillin)
What are ESBLs?
Extended spectrum beta-lactamases;
- produced by Gram negative bacteria
- break down third generation cephalosporin and penicillin, therefore resistant to all beta-lactams
What are CPE?
Carbapenemase producing enterobacteriaceae
- Gram negative bacteria that are resistant to carbapenems (a broad class of antibiotocs)
- often resistant to many other antibiotic classes
- leaves no antimicrobial therapy options
What is a penicillin binding protein (PBP)?
Enzyme used in peptidoglycan synthesis, normally inhibited by penicillins/cephalosporins
Give examples of a bacterial species that become resistant through PBP target site alteration?
MRSA
Penicillin resistant streptococcus pneumoniae
