WEEK 4 - Beta Lactamases Flashcards
What are beta-lactams and their MoA
A class of antibitoics
- Have a beta-lactam ring
- Popular class of antibiotic, used in humans and livestock (food chain)
MoA:
- PBP binds to beta-lactam instead of glycan strains = NO glycan crosslink chains formed = cell wall rigidity is compromised
- Bacteria lyses as it can’t withstand osmotic pressure
MoA of Bacterium:
- Bacterial cell wall uses PBP (penicillin-binding protein) to bind / cross link D-ala on end of glycan strains (NAM) = peptidoglycan fomed
- Peptidoglycan / crossliniking prevents cell from bursting under pressure = bacteria able to survive
List 3 sub-classes of beta-lactam antibitoics
- Penicillins
- Cephlasporins
- Carbapenems
How have bacteria evolved / found ways around beta-lactams
4 ways they resist antibiotics
- Upregulation of efflux pumps to remove b-lactam out of cell
- Down regulation of outer membrane porins = stops entry of b-lactam
- unable to cross cell wall (outer membrane)
- Mutation of PBP active site to avoid it binding b-lactam
- e.g. MRSA bacterium cells completely change its PBP
- main mechanism of gram +ive bacteria
- Produce beta-lactamases to inactivate b-lactam
NOTE:
- these mechanisms can occur simultaneously
- changing antibiotic regimes introduced selection pressures amongst bacteria
- e.g. as use of antibiotics ↑ more bacterias are able to produce enzyme against antibiotic
What are beta-lactamases
inc. 2 types
Enzymes that hydrolyse the beta lactam ring (in beta-lactams), inhibiting the antibiotic + making it inactive
- Hydrolysation prevents PBP from binding to antibitoic
Beta lactamases are classified into 2 types:
1. SBLs (serine b-lactamases)
- Class A, C and D
- have a deep active site
- have serine (+ lysine) active site
2. MBLs (metallo b-lactamases)
- Class B (3 subtypes: B1, B2, B3)
- have a shallow active site
- have 2 zinc at active site + hydroxyl (OH-)
- MoA OH- attakcs b-lactam ring = opens it = forms aceylated form
List the 3 types of beta-lactamases
- Penicillinase
- 1st enzyme activty recorded
- ESBLs
- active agaisnt 1st-3rd gen. cephalosporins
- active against penicillins
- Carbapenemase (produced by CPEs)
- have activity against amolst ALL b-lactams inc. carbapenems
ESBLs INFO
ESBL – extended spectrum beta lactamases
ESBLs developed due to mutation (from serine to glycine at active site of exisiting beta-lactamase)
- Able to hydrolyse 1st to 3rd gen. Cephlasporins (beta-lactam antibiotic)
- Can NOT hydrolyse carbapenems = ↑ reliance on carbapenems
- Plasmid can spread quickly and easily = resistance is transffered between bacterias
- ↑ risk of spread in hospital setting
Can be INHIBITED by CLAVULANIC ACID
- C.acid acts like a beta-lactam antibitoic (similar structure) = ESBL tries to hydrolyse this instead
= Antibitoic remains active
What are CPEs
CPE = Carbapenemase producing Enterobacteriaceae
- bacteria which produced carbapenemase
- Beta-lactamase produced was able to HYDROLYSE almost ALL beta-lactam antibiotics (penicillin, cephlasporin, carbapenems etc.)
- Encoded in plasmid which is very transmissible = lactamase resistance can spread to other bacterias
- Limited treatment options against CPEs
- ↑ mortality, ↑ time spent in hospital, ↑ healthcare costs (screening, infection control to prevent spread of CPE)
NDM-1
NDM-1 is a newer carbapenemase producing enzyme
- Endemic in india and pakistan
- Has a rapid spread
- Is a metallo beta-lactamas (has zinc in active site not serine)
- Is plasmid-mediated
What are the current beta-lactam antibioitic treatments options
- Beta-lactam AND beta-lactam inhibitor
- e.g. Amoxicillin and Clavulanic acid = Co-amoxiclav
- Carbepenems
- resistant to ESBLS
- e.g. Imipenem or meropenem
- ONLY used for invasive, life-threatening infections
- Ertapenem
Penicillin INFO
Examples,
Penicillins are a subclass of beta-lactams (class of antibiotics)
Examples:
- Penicillin G (IM/IV)
- 1st penicillin
- had narrow spectrum
- Penicillin V (oral)
- Ampicillin (oral/IV)
- added amino group ↑ spectrum of activity against bacteria
- Amoxicillin (oral/IV)
- most newest
- has broad spectrum of activity
Cephalosporins INFO
Are a subclass of beta-lactams
- Have natural structural RESISTANCE TO BETA-LACTAMASES
- penicillinase (lactamase) is unable to break it down
- BUT could be hydrolysed by ESBLs (only 1st to 3rd gen) - Have 5 generations
- 3rd gen targetted mainly gram -ive bacteria
- Gen. 5 cephlasporins = only antibitoic able to kill MRSA
Carbapenems INFO
A subclass of beta-lactam antibiotics
- LAST LINE intervention for multi-drug resistant bacteria
- Stable against ESBLs / beta-lactamases
- due to structural changes
- has no sulphur present only carbon - BUT CPEs (carbapenemase resistant bacteria) developed due to ↑ use of carbapenems
- Have a BROAD spectrum of activity
- Mainly active against gram -ive bacteria
NOTE:
- 1st carbapepenem discovered was very unstable, so was chemically modified
- modifications ↑ its shelf life
What is the MoA of Carbapenems
WATCH VIDEO
Active agaisnt PBP AND b-lactamases
- Serine (from PBP) attacks b-lactam ring (in carbapenem) openeing the ring
- The 6a-hydroxyethyl group on the β-lactam ring in carbapenem traps glutamate / water group (from lactamase) in a non-reactive orienation
- B-latam undergoes tautomerisation (revrsible switch between diff. forms) in the b-lactamase active site = a stable, inert, aceylated form of drug fromed
- Stable form makes it harder for the lactamase to attacl the β-lactam ring
= de-acylation can NOT occur - Acyl-enzyme intermediate formed shifts the C=O out of the oxyanion hole
= less stable and slows down the deacylation process
Polymxins INFO
NOW th last line of defence as carbapenems became overused
- Are cyclic peptides
- MoA: disrupt inner and outer membrane of bacterial cell
- i.e. tears apart membrane
How are microbiologists / HCP combatting lack of treatment options
- Re-purposing old drugs (not commonly used)
- e.g. Temocillin - narrow spectrum of activity (can resist ESBL and CPE action)
- Developing new lactamase inhibitors
- Effective infection control (to ↓ spread)
- Antimicrobial Stewardship
- i.e. not overusing antibitoics
- Developing new antibiotics
