CPEs - Resistance Mechanisms Flashcards
Talk about Carbapenems
NB: theres a good piece on the clinical significance at the end of the lecture
B-lactams with broad spectrum of activity against Gram negative pathogens
Last effective defence against MDR strains e.g. E. Coli or K. pneumoniae
Talk about carbapenemases
There are over 2000 classes
Class A: KPC
Class B: metallo B-lactamsases (VIM, NDM, IMP)
Class D: OXA-48 and OXA-181
Genes can be plasmid-located and associated with transposons and integrons - ability to spread
List the big 5
KPC
OXA-48
IMP
VIM
NDM
Give some examples of Class A and what do they mediate resistance against
KPC
Resistance against penicillins, cephalosporins, carbapenems and aztreonam
What inhibits class A such as KPC
Boronic acid and avibactam
Give some examples of Class B and what do they mediate resistance against
VIM
NDM
IMP
Resistant agains all B lactams but aztreonam
What inhibits class B such as IMP, NDM and VIM?
EDTA and dipicolonic acid
Give some examples of Class C and what do they mediate resistance against
CMY -> not noe of big five
Penicillins, cephalosporins and aztreonam -> not reistant to carbapenems
What inhibits class C such as CMY
Cloxacillin
Borionic acid
Avibactam
Give some examples of Class D and what do they mediate resistance against
All the OXAs, 48, 23, 51, 24, 58 etc
Resistance to penicillins, cephalosporins, carbapenems and aztreonam
What inhibits class D such as OXA-48
Avibactam
What does KPC stand for?
K. pneumoniae carbapenemase
What is KPC, talk about it
Most common carbapenemase worldwide
Transposon encoded
Class A
Endemic - worldwide spread
Has spread to Enterobacterales, P. aeruginosa and acinetobacter spp
High mortality 50% or more due to MDR
Mediates resistance to carbapenems, penicillin, cephalosporins and aztreonam
What is KPC found in?
Initially found in K. pneumoniae
Has spread to Enterobacterales, P. aeruginosa and acinetobacter spp
Comment on spread of KPC
First reported in USA in 1996 but now worldwide spread
First isolate in Greece in 2007 now spread to most acute-care facilities within 2 years
What clone of KPC is responsible for worldwide spread?
ST-258
What are KPCs resistant to?
Mediates resistance to carbapenems, penicillin, cephalosporins and aztreonam
Mortality of KPC
50%
List the Class B: Metallo-B-lactamases were concerned with
VIM/IMP
NDM-1 -> New Dehli metallo-B-lactamase 1
Talk about VIM/IMP
Class B
51 variants
Integron encoded
Reported worldwide
Spread to Enterobacterales, Pseudomonas and Acinetobacter sp
Death rates between 18 and 67%
High level of production can produce resistance to all carbapenems, penicillins and all cephalosporins
NB: SUSCEPTIBLE TO AZTREONAM
What organisms are VIM/IMP found in?
Spread to Enterobacterales, Pseudomonas and Acinetobacter sp
Talk about the spread of VIM/IMP
Discovered in Japan in 1990s now reported worldwide
Higher prevalence in southern Europe and Asia
Spread to many Enterobacterales, Pseudomonas and Acinetobacter species
What is the mortality associated with VIM/IMP
Pseudomonas and Acinetobacter sp
Death rates between 18 and 67%
What is VIM/IMP resistant against?
High level of production can produce resistance to all carbapenems, penicillins and all cephalosporins
What is the telltale sign of a VIM/IMP
NB: SUSCEPTIBLE TO AZTREONAM
-> indicator on vitek
Talk about NDM
New Dehli metallo-B-lactamase 1
Class B
16 variants
Plasmid-mediated
Originated in New delhi in 2008 but now in 40 countries
Mostly in E. Coli and K. pneumoniae
Major public health concern as it can spread in envirnoment, getting into water etc -> often multiple clones associated in spread
Resistant to carbapenems, penicillins, cephalosporins
Susceptible to aztreonam
How is NDM spread
Plasmid mediated
Talk about spread of NDM
Originally in New Dehli in 2008
Now in 40 countries
Hotspots in India and Pakistan
Common in UK
Outbreak in 2019 in Tuscany of 227 cases
Mostly in E. coli and K. pneumoniae
What is NDM found in
E. Coli
K. pneumoniae
What is NDM resistant to
Resistant to carbapenems, penicillins, cephalosporins
What is the telltale sign of NDM
Susceptible to aztreonam
Talk about OXA-48 type
Class D
Many variants e.g. OXA-181 etc
Plasmid and transposon encoded
Originated in Turkey but rapidly spread across Europe
Fastest growing GP in Europe - now endemic in Malta and Turkey
Mortality unknown
Associated with E. Coli and K. pneumoniae
Mediates resistance to carbapenems and first generation cephalosporins
Little activity against broad spectrum cephalosporins or aztreonam
But very difficult to detect so true prevalence understimated
How is OXA spread
Plasmid and transposons
How has OXA spread
Oringially from turkey
reports alarmingly increasing in europe
Fastest growing CP in Europe
Endemic in malta and turkey
Associated with E. coli and K. pneumo
Mortality for OXA
Unkown
Associated organisms with OXA
E. coli and K, pneumo
Resistance mediated by OXA
Mediates resistance to carbapenems and first generation cephalosporins
Little activity against broad spectrum cephalosporins or aztreonam
Telltale sign of OXA
Little activity against broad spectrum cephalosporins or aztreonam
Talk about transmission of carpanemases
CP enzyme carried on mobile genetic elements such as plasmids or transpons
HGT -> sharing of plasmid amongst gut flora
NB in infection control
Confers resistance to multiple organims, limiting treatment
How might you identify an OXA-48
May be fully susceptible to cephalosporins unless an ESBL or AMPC also present
How would you identify an metallo-B-lactamase producer such as VIM/IMP or NDM
Susceptible to aztreonam unless ESBL or AMPC also present
What are the resistance profiles of CPEs
They all hydrolyse penicillins, most cephalosponrsins and some carbapenems and aztreonam - depends on group
OXA-48 CPs may be fully susceptible to cephalosporins unless also an ESBL or AmpC
MBLs are suscpetible to aztreonam unless ESBL or AMPC
However resistance phenotype can vary depending on the level of expression and association with other resistance methods e.g. effllux or permeability - MDR etc
What are the problems with identifying carbapenemase producers
Not all CP producers are resistant to carbapanems
ESBLs/AmpC + porin loss can appear like a CP producer but isnt actually (CPOs vs CREs)
Other methods of Carbapenemase resistance other than carbapenemases
Intrinsic resistance to CPs
Intrinsic Carbapenemases
Loss of porin and/or efflux
ESBL or AmpC + impermeability
Where is intrinsic resistance seen
Non-fermenters resistant to ertapenem only
Serratia species and proteeae -> poor susceptibility to imipenem
Intrinsic carbapenemase
Stenotrophomonas maltophilia
Aeromonas spp
Acinetobacter baumannii
Loss of porin and/or efflux
P.aeruginosa
ESBL or AMP C + impermeability
Mostly Enterobacter and Klebseilla
Rarely in E. coli
Talk about trends in Carbapenem resistance in Europe
Resistance increased by more than 50% compared to 2019
ST23-K1 K. pneumoniae rapidly increasing - these are hyper virulent and invasive
Talk about trends in Carbapenem resistance in ireland
1.5% increase since 2019
Lots of different outbreakd - associated with travel
small outbreaks e.g. oxa-48 in tallagh hsopital k. pneumo
List the different outbreaks of CPOs in ireland - from beginning to 2022
2022: 26 outbreaks of CPE in healtchare - all OXA-48
2016-2017 largest outbreak in Dublin (OXA-48 >180 cases in 1 year)
2016 small outbreaks of VIM in mayo and NDM in waterford
2012-2016 -> regional spread, rise in CPE cases in general
2011: OXA-48 K. pneumoniae in Dublin - 12 patients
2011: first outbreak (KPC) in two hospitals, 9 patients in the midwest
2009: first sporadic CPE cases in Ireland - most linked to travel - KPC, VIM, NDM
Results from surveillance
861 confirmed CPEs in 2022 found through surveillance
88% were colonisation
10% were noninvasive infection
2% were invasive
OXA-48 most common at 73% of all CPEs in Ireland
Most common CPE in Ireland?
OXA-48
73% in 2022
How are CPEs changing in Ireland over the years (2018-2022)
OXA-48 increasing by 12%
KPC decreasing by 25%
NDM increasing by 185%
VIM increasing by 200%
Public Health Emergency statement
Minister Harris addressed CPE in 2017
Importance of detection
Need a catch all method - diversity of enzymes, variation, expression etc, no ideal indicator
Have to screen, confirm and characterise CRE producers
Distinguish from AmpC b -lactamases
Who are we screening
ICU
Haematology/oncology/transplant
renal dialysis
transfers
previoius cpe or contact with cpe
How do we identify KPC in the lab
Meropenem resistant
Synergy with boronic acid only
= KPC or other class A CPO
How do we identify an AmpC CPE
Meropenem resistant
Synergy with boronic acid and cloxacillin (a derivative of oxacillin - a penicillin)
= AmpC + porin loss
How do we identify an MBL
Meropenem resistant
Synergy with dipicolinic acid only
= Metallo-B-lactamase (MBL) e.g. VIM/IMP or NDM
How do we identify an OXA-48
Meropenem resistant
No synergy with any of the acids
NB: Temocillin resistant
Telltale lab ID of OXA-48
Temocillin resistant
How do we ID a ESBL with porin loss
Meropenem resistant
No synergy
Temocillin susceptible
=ESBL plus porin loss
What would Mero R but synergy with boronic acid indicate?
KPC or another class A CPO
What would mero R but synergy with boronic acid and cloxacillin indicate
AmpC plus porin loss
What would mero R but synergy with dipicolinic acid indicate?
MBL such as VIM/IMP or NDM
What would Temocillin resistant indicate
OXA-48
What would Mero resistance but no synergy and temocillin susceptible indicate?
ESBL with porin loss
How do we select the right carbapenem to use fot testing
use of eucast defined screening cut offs
Meropenem and ertapanem are used
- poor sensitivity with imipenem so its not used
Method used
need a method that will catch all
List the different methods of detecting CPEs
Chromagar and rectal swabs
Combination disk test (Rosco/MAST)
Double disc synergy test
Gradient strip tests e.g. imipenem + imipenem + EDTA
Combination disc tests
Clorimetric tests to detect hydrolysis
MALDI-TOF to detect hydrolysis
Immunochromatographic test to detect carbapenemase antigens
Check Direct CPE
Gene Xpert Carba-R
LightMix modular Kits
Talk about the different agars for CPEs
Used to screen only as sens poor especially for OXA-48
Brilliance CRE 82% sens
ChromID/Super CARBA >95% sens
-> oxa-48 sens only 30% for both
Split agar combining CARBA with OXA-48 selective agar increases sens to 61% for OXA
Talk about the combination disk tests
Also known as ROSCO or MAST disks
Comparing meropenem to selective inhibitors to distinguish between carbapenemase ty[es
Confirms CPE if zone size is greated with inhibitor
List the Rosco disks
Meropenem + boronic acid = KPC
Meropenem + cloxacillin = AmpC
Meropenem + dipicolonic acid = IMP, NDM, VIM
Temocillin = R = Oxa48
What will the Rosco discs be labelled as
MRP10 = meropenem
MRPBO = mero + boronic acid
MRPDP = mero + dipicolonic acid
MRPCX = mero + cloxacillin
TEMOC = temocillin 30ug
Talk about the gradient strips for CPEs
Imipenem on one end
Imipenem plus EDTA on other end
Any synergy = positive
For the inhibitor combination disc test what is used
Carbapenem only
Carbapenem + MBL inhibitor
Carbapenem + KPC inhibitor
Carbapenem + AMPC inhibitor
What are the pros of inhibitor based tests for CPEs
Cheap
easy to perform
Most extensively evaluated - recommended by eucast for labs without special expertise in B-lactamase detection
What are the cons of inhibitor based tests
Some MBL inhibitors such as EDTA act non-sepcifically -> will inhibit other CPEs
Can lack sens if enzyme expressed at low levels
Difficult to interpret if multiple resistance mechanisms are present
We have no inhibitor for OXA-48
Overnight incubation required
List some of the colorimetric tests for CPEs
CarbaNP and Blue-Carba test
B CARBA test
What are the pros and cons of colorimetric tests for CPEs
Results in less than 2 hours
Good sens and spec
Subjective interpretation based on colour
False negatives with mucoud strains and some enzymes -> K. pneumo
Not all primary culture medium works with test
Talk about MALDI to detect CPEs, pros and cons
Detects hydrolysis
Uses Bruker MBT STAR Carba IVD kit and software
Pick colonies and resuspend in antibiotic solution then inc for 3 hours
Can be done on isolates and blood/urine
Not for in house as will have to change MALDI settings
Issues with detecting some enzymes
Talk about immunochromatographic tests for CPEs
Detect carbapenemase antigens
RESIST-4: KPC, OXA48, NDM, VIM
CARBA 5: KPC, OXA-48, NDM, VIM, IMP
Excellent sens and spec from colonies and spiked blood cultures
Results in 15 mins
some issues with false negatives
Talk about check direct for CPEs
Identifies CPE carriers directly from rectal swabs or cultures in 2 hours
Detects clinically prevalent carbapenemases (IMP excluded)
More sensitive then culture
Talk about GeneXpert Cepheid Carba-R for CPE
Rectal swabs
All 5 CPEs
High sens, spec, ppv, npc all over 95%
accurate and rapid with less than 5 mins hands on time
55 euros per test
Talk about the LightMix for CPEs
Uses LightCycler
Direct detection of colonised patients
Used in mater
Rectal swabs or blood cultures
99% sens, 100% spec
TAT about 2 hours
Only ran in batches though
Very cheap only 14 euros per test
Clinical implications for CPEs
Public health threat
Community
Random outbreaks
High mortality
Carriage linked to infection
Rapid dissemination through mobile genetic determinants
prevention reliant on early active surveillance
Can be difficult to distinguish - special screening methods needed
Talk about the general mortality with CPEs
x3-x6 times higher with CRE infection
mortality between 30 and 75%
65% of CRE BSIs
Delays in treatment or treatment unavailable
Talk about CPE carriage and infection link
17% carriage overall but 90% linked to infection
