AMPC and ESBLs - Resistance Mechanisms Flashcards

1
Q

What are our ESKAPEE organisms?

A

E. faecium
S. aureus
Klebsiella
Acinetobacter
Pseudomonas
Enterobacter
E. Coli

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

In general what resistance are we concerned with in gram negatives

A

B-lactamase mediated resistance emerging at an alarming rate

Increased resistance to aminoglycosides and quinolones

MDR GNBs becoming an epidemic public health threat

Clonal spread of resistant phenotypes e.g. epidemic strains of E. coli and klebsiella

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

Talk about B-lactamase mediated resistance in GNBs

A

ESBLs -> transferable resistance seen in Klebsiella pneumonia and E. coli

Chromosomal AmpC -> E.cloacae, C. fredii, S. marcescens, P. aeruginosa and M. morganii

Plasmid mediated AmpC -> transfers resistance

CPE - ‘Big 5’ -> P. aeruginosa, Enterobacterales

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

Give the common different resistance mechhanisms in GNBs

A

Porin reduction to decrease permeability

Broad-specificity efflux pumps

Beta-lactamase enzymes

Target site modification - Beta-lactam-insensitive cell-wall transpeptidases

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What are the different classifications of B-lactamases?

A

Bush system - Functional classification

Ambler system - Structural classification

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

Talk about the Bush system of classifying b-lactamases

A

Divided into 4 primary class (1-4) based on functionality

Not really used anymore as organisms could gain mutations which would result in them changing classes

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

Talk abut the Ambler system

A

Categorised into 4 molecular groups A to D
Offers stability against mutations that may influence enzyme activity

The majority of clinically significant B-lactanases re found in Ambler A and C

This system is used over the Bush system nowadays as these are more stable categories

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What are the Ambler class A?

A

Serine beta-lactamases
Works on penicillins, early cephalosporins with ESBLs working on 3rd generation cephalosporins
Inhibited by clavulanate

Examples include ESBLs (CTX-M) and carbapenemases such as KPC

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

Talk about Ambler class B

A

Metallo-beta-lactamases

Broad spectrum including carbapenem resistance but not monobactam resistance

NDM, VIM and IMP

Require zinc for their activity

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

Talk about Ambler class C

A

AmpC beta-lactamases

Resistance to penicilliins, cephalosporins (1st and 3rd gen), monobactams not but not carbapenems

Example = AmpC

Can be Chr or plasmid mediated - inducible in some bacteria e.g. enterobacter

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

Talk about Ambler class D

A

Oxacillinases (OXA)

Penicillins, cloxacillin, carbapenems

OXA-48 = example

Common in Acinetobacter and CR-enterobacterales

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What is the mechanism in AmpC B-lactamases

A

A type of Class C, Group 1
They are typically chromosomally encoded but can also be plasmid-mediated -> therefore less likely to see transmission
AmpC enzymes hydrolyse penicillins and cephalopsorins including many third gens

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What is the resistance spectrum of AmpC B-Lactamases

A

Active against penicillins, cephalosporins (including cephamycins like cefoxitin) and monobactams

Not inhibited by clavulanic acid but may be inhibited by substances like boronic acids or cloxacillin

Resistant to third-generation cephalosporins like ceftriazone and cefotaxime but are less susceptible to B-lactamase inhibitors

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

What are the most common AmpC organisms

A

Enterobacterales like Enterobacter spp, Citrobacte freundii, Serratia marcescens and Pseudomonas aeruginosa

Also seen in plasmid-mediated forms in E. coli and Klebsiella species

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

Talk about the clinical relevance of AmpC B-lactamases, how do we detect it

A

Resistance can emerge via the induction or depression of chromosomal AmpC genes
Use of cefoxitin or cefepime in testing can help identify AmpC producers

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

Talk about Extended-Spectrum B-lactamases

A

ESBLs are an Ambler clas A B-lactamases

ESBLs are a major public health threat associated with significant morbifity, mortality and increased healthcare cosrs

They hydrolyse most penicillins and cephalosporins including cefuroxime and 3rd and 4th generation cephalosporins

Have no activity on cephamycins or carbapenems

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

What is the resistance profile of ESBLs

A

Resistant to most penicillins and cephalosporins e.g. cefuroxime, cefotaxime, ceftrazidime and ceftriaxone also aztreonam

No activity against carbapenems or cephamycins such as efoxitin and cefotetan

Inhibited by clavulanic acid, sulboactam and tazobactam

Level of expression nad presence of other mechanisms such as AMP C leads to a variety of resistance phenotypes

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

What do ESBLs have no activity against?

A

No activity against carbapenems or cephamycins such as efoxitin and cefotetan

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

What is ESBL inhibited by

A

Inhibited by clavulanic acid, sulboactam and tazobactam

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

What are some of the different mutants of ESBLs

A

TEM and SHV

CTX-Ms such as CTX-M-15

OXA

VEB

PER

GES

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

Talk about TEM and SHV mutants, how did the originate

A

Original ESBLs

Mainly drive resistance in healtchare

Arose form mutations in the parent beta-lactamases found in Escherichia coli (TEM) and Klebsiella pneumonia (SHV)

22
Q

What is the mechnism of TEM and SHV ESBLs

A

Mutations in the TEM and SHV genes typicaly result in the substitution of specific amino acids in the beta-lactamase active site, allowing these enzymes to break down a broader range of beta-lactam antibiotics

Ability to hydrolyse exended-spectrum penicillins and 3r and 4th generation cephalosporins

23
Q

Talk about CTX-Ms

A

Dominant ESBL enzymes globally
Resistance in both hospitals and CA infection
Widespread in common pathogens such as:
- E. Coli - most frequent carrier in community infections
- Klebsiella pneumoniae - especially in healthcare-associated infections
Resistance is spread due to plasmid-mediated mobility facilitating horizontal gene transfer

24
Q

Spectrum of CTX-Ms

A

They hhydrolyse third generation cephalosporins e.g. cefotaxime and ceftriaxone

25
How do we detect CTX-Ms
Resistant to cefotaxime (marker) Will also be resistant to ceftriaxone
26
Talk about the mechanism of resistance in CTX-Ms
CTX-M genes encoded on plasmids and often co-locate with resistance genes for other antibiotic classes such as aminoglycosides or fluoroquinolones Mobility of genes allows rapid dissemination across species and geographical boundaries - hence widespread Mobility also allows co-resistance - MDR through linkage with other resistance determinants
27
What is the most prevalent CTX-M ESBL vaiant?
CTX-M-15 global variant - known for its efficient dissemination
28
Talk about the OXA variant of ESBL
A type of Class D organism Primarily oxacillin-hydrolysing enzymes, associated with carbapenem resistance
29
Talk about the VEB, PER variants of ESBLs
ESBLs found occasionally in Pseudomonas or Acinetobacter
30
Talk about the GES variant of ESBLs
A rare group that can confer resistance to carbapenems in addition to cephalosporins
31
Talk about rates of ESBL E. Coli in Europe
Decrease of 3.6% compared to 2019 Ireland consisent at 10% seen over last 5 years Bulgaria at 40%
32
Talk about 3rd generation cephalosporin resistant KLPN in europe
34.8% on average Bulgaria at 80%
33
How can you distinguish a TEM and SHV ESBL from a CTX-M ESBL
TEM and SHV are resistant to ceftazidine but variable to cefotaxime CTX-M are resistant to cefotaxme but variable to ceftazidine
34
What should you do with a positive ESBL
Must distinguish an ESBL from: - AmpC B-lactamase - Carbapenem hydolysing B-lactamase
35
How would you screen or an ESBL
Put up against cefotaxime and ceftazidine -> if resistant to one or both = ESBL If AmpC ESBL confirm with cefepime +/- clavulanic acid If ESBL variant confirm with ceftazidime and cefotaxime +/- clavulanic acid -> if intermediate query AmpC and test accordingly
36
What combination of antibiotics are used fr ESBLs
Cefotaxime or ceftriaxone AND ceftrazidime or cefpodoxime
37
Talk about agar for ESBLs
ESBL chromagars are available for use with rectal swabs - Chromagar 98% sens, 72% spec - ChromID 98% sens, 73% spec - Brilliance 99% sens, 58% spec No medium is fully ESBL selective though - derepressed AmpC B-lactamase and P. aeruginosa Complementary tests needed to confirm
38
What is the marker of all ESBLS
Cefpodoxime resistance seen in all ESBLs but low level resistance is common ni the absence of ESBLs Cefpodoxime most sensitive individual indicator but lacks specificity -> combination of cefotaxime and ceftrazidime allows for better specificty
39
What is the marker for TEM and SHV
Ceftazidime resistance
40
What is the marker for CTX-M resistance
Cefotaxime resistance
41
What is the molecular detection method for ESBLs
Check-Direc ESBL
42
Talk about Check Direct for ESBLs
Can identify ESBLs directly from rectal swabs in 2 hours Covers clinically prevalent ESBLs: CTX-M-1, CTX-M-2, CTX-M-9 and SHV Early studies show good performanc and greated sensitivity then culture Detects 80 CTX-M, 160 TEM, 110 SHV variants
43
What are some of the common confirmatory tests for ESBLS
Combinaion disk test Double-disk synergy test Gradient strips
44
Talk about the combination disk test for ESBLs
Ceftazidime + ceftazidime + clavlanic acid Cefotoxime + cefotozime + clavulanic acid Cefepime + clavulanic acid or AmpC inhibitor to detect AmpC activity >5mm increase in zone indicates an ESBL
45
Talk about double-disk synergy test
Expansion of indicator cephalosporin inhibition zon towards amox/clav (augmentin) disk -> augmentin and cefodoxime Disk spacing is critical -> may be reduced or expaned for strains with high or low level of resistance Either use of cefepime disc or add clox to agar for AmpC producers
46
Talk about gradient strips for ESBLs
Double ended strip - cephalosporin + cephalosporin + clav >8 fold reduction in MIC = ESBL Phantom zone in middle = ESBL Deformed ellipse = ESBL Non determinable could be due to AmpC activity - should test cefepime/clav
47
What are the pros and cons of each ESBL confirmatory method?
Double disc test: cheap but best disc spacing varies with strain Combination disc test: cheap, does not require critical spacing, sensitive and specific but batch variation and negative controls critical Gradiant strip: sensitive, accurate, internally controlled, mor epensivr
48
What bacteria do we not screen for ESBLs for
Theres no test developed for Acinetobacter spo and P. aeruginosa Stenotrophomas maltophilia also causes false positives
49
Why can we not ESBL screen for acinetobacter
Acinetobacter spp is often susceptible to clavulanate alone
50
Why do we not have an ESBL screen for P. aeruginosa
ESBLs are not common in these and should not be sought routinely ESBL should only be considered in ceftolozane/tazobactam resistant isolates
51
Why do we not have an ESBL screen for Stenotrophomonas?
S. matlophilia can cause positive results due to inhibition of L-2 chromosomal B-lactamase ubiquious in the species