Evolution of Beta Lactamases Specificity: Carbapenemases and Beta-lactamase inhibitors Flashcards
Name the Class A Beta=lactamases
BlaZ (S. Aureus, penicillinase)
TEM, SHV, CTX-M (ESBLs, enterobacteriaeceae
KPC (Carbapenamse: eneterobacteriaceae)
Name the Class C Beta-lactamases
AmpC, CMY
Name the Class D Beta-lactamases
OXA (carbpaenase resistance in A. Baumaani and Enterbacteriaceae)
ame the Class B beta-lactamases
IMP, VIM (found in non-fermenting bacteria e.g. P, aueginosa)
NDM (in enterbacteriaceae)
These are generally broach spectrum including carbapenemases and whislt most are chromosomal there are the above worrying examples on plasmids
Describe teh structure of pencillins
All have the beta lactam ring but fused to a 5 member S containing rign
Describe the structure of cephalosporins
Beta lactam ring fused to a 6 member S containing ring and double bond
Describe the structure of carbapenems
Beta lactam ring fused to a 6 member S containing ring with a double bond
Descrbie the structure of monobactams
Beta-lactam ring but not fused to anything
Describe the structure of Clavulanate (inhibitr)
Bi-cyclic beta lactam containing molecule reminescent to pencillins
Poor antimicrobila activity but good inhibitor action
What has happened to resistance spectrum in Class A beta-lactamses
Resistance has been progressively increasing particularly in class A Carbapenamase activity has even been seen now
Summarise evolution of beta-lactams in response to b-lactamases
1) Penicillins produced –> only had gram+ve activity and BlaZ conveyed resistance
2) Aminopenicillins made –> meant that had activity against gram -ves. But then TEM and SHV conveyed resistance
3) Cephalosporins introduced –> BUT TEM and SHV mutations conveyed resistance them
4) Oxy-amino 3rd Generation cephalosporins introduced to combat TEM and SHV resistance –> mutations in TEM and SHV to convey resistance . Also emergenec of CTX-M
What is the solution to Class A Beta Lactamases
Combination therapy with inhibitors!
Clavulanic acid, tazobactam, sulbactam
How do beta-lactamase inhibitors work
They have a bicylcic- beta lactam structure hence from an acyl-enzyme species by reacting with the active site serine in the Beta-lactamases
Enzyme cant break down the same was as a beta lactam
Get a range of fragmentation reactions – > throguh complex intermediates the result is a covalently modified species where the active site serine has reacted with a fragmentation product
The beta lactamase is permantily nhibited
Resistance to beta-lactamse inhibitors in TEM and SHV has arisen how
244 - mutation inactivates the water moleule that catalyses the fragmentation reactoin
130 - mutation modifies the active site structure to improve inhibitor binding
HOWEVER the mutations conveying resistance to inhibitors are mutually exclusive to those conveying ESBLs
What are the mecahnisms of carbapenem resistance
1) Permeability modification & weak enzymes
2) Acquired serine carbapenemases e.g. KPC and OXA48
3) Metallo-B-Lacatmases: IMP, VIM, NDM
How can permeability modification and weak enzymes convey carbapenem resistance
Reduction in permeability with a weak enzyme can be enough to convey resistance without the enzymes strictly being a carbapenemase. E.g. ESBL/ AmpC
P. Aureginosa is an example of this: Loses OprD porin and combo with a weak enzyme can provide resistanct
What is the KPC carried in
Acquired serine carbapenemase on Tn 4401b composite transposon
Only carried on a few restricted strains of Klebsiella
Global enzymes –> particular problem in Northern England
Freeuqnelty get multirestance
What is the normal action of carbapenems
Carbapenems have a hydroxyethyl substituent unique to them
They can acylate and inhibit both PBP and Serine Beta-Lactamases to cause their effects –> the OH bond on the carbapenem forms a H bond to water, hence deactivating it and preventing it from deacylating and inactivating carbapenems
How does KPC convey carbapenem resistance
Active site modification in the B-lactamase –> binds carbapenem in a slightly different orientation –> the hydroxyl carbapenem group is too far from the water to form a H bond –> hence water can still deacylate the beta lactam ring and hence degrades the antibiotics
name inhibitors that can target KPC
Avibactam
Vaborbactam
How does avibactam work
Has a beta-lactam like structure Reacts with the serine of beta-lactamases reversibly to form acyl intermediate enzymes that cant be hydrolysed Active against class A and class C
How does vaborbactam work
It is a cyclic boronate inhibitor of class A and C
Has a Beta-lactam like structure
Contains a boron and carboxylic acid –> can form an acyl enzyme to the active site serine attached to the Boron
The Boron is conducive to a tetrahedral sturcuter –> mimics the tetrahedral transition state
Approved in combo with eropenem
What is OXA48
It is an acquired Class D serine carbapenemase
Causing increased numebrs of carbapenem resistance in the UK
May overtake KPC as the primary method of carbapenem resistant plasmid carried
What are the most common MBLs
NDM and VIM
Where is NDM found
Particularly found in clinical strains of enterbacteriaceae e.g. Klebsiella –> however NOT restcited to a few strains unliike KPC and is present on many plasmid types
Where is VIM 2 found
Important in non-fermenting bacteria e.g. P. auerginosa
What p. eurginosa clone is associated with VIM B-lactamses
ST235 strain !!
How can we tackle this carbapenem resistance
There was the option of avibactam and vaborbactam inhibitors
HOWEVER CLass D are insusceptible to these inhibitors
Colisitn is a last resort but is effective against many MBL producers
What can MBLs hydrolyse
Virtually anything with a beta-lactam ring
