ESBL. antimicrobial R Flashcards
What are the 2 main categories of resistance?
- Intrinsic- normal genetic,structural, physiological state of a microbe, natural and inherited. predictable for some bacterial groups- pseudonomads R to augmentin
- Acquired- successful genetic mutation
- Acquisition of genes from other organism(s) via gene transfer - Combination of a mutation and gene transfer
Genetic changes lead to altered cellular physiology and structure
Horizontal Gene transfer- describe conjungation, transduction and transformation
conjungation- by plasmids or transposon
transduction- by bacteriophage
transformation - direct transfer of DNA between compatible species
What is the antibiotic creed MINDME
Microbilology guides therapy wherever possible
Indications should be evidence based
Narrowest spectrum required
Dosage appropriate to the site and type of infection
minimise duration of therapy
ensure monotherapy in most cases
How can B lactamases be mediated?
By plasmid or chromosome
Production/Expression
- May be secreted into the surrounding environment e.g. S. aureus
- Cell bound in most Gram negatives
* Only become effective
once antimicrobial enters the cell wall
- Inducible (e.g. S. aureus)
* Onlyproducediforganismisexposedtoab-lactamantimicrobialinitsenvironment
- Constitutive (most Gram negatives)
* Producedconstantlywhetherthereisademandornot
- Constitutive-Inducible – constant low-level production with induced production of higher levels when required/exposed to a b-lactam antimicrobial in its environment
TEM 1, 2, SHV-1 B lactamases - how can they be mediated?
where is tem 1 and 2 commonly found?
what does it mean tem 1 and 2 in terms of R and S?
All three are chromosomal OR plasmid mediated
All three have constitutive OR inducible expression
Tem 1 and 2 Present in many Gram-negative organisms (very common) - Enterobacteria (Enterobacteriaceae)
- Haemophilus influenzae
- Neisseria gonorrhoea
Resistance to 1GC (exception is cephalexin), 2GC and penicillins (including AMX, AMP)
* Susceptible to 3GC and 4GC
* Enzymes are inhibited by clavulanic acid, tazobactam, sulbactam, avibactam, vaborbactam
where is SHV1 mainly found
what is it S and R to?
Klebsiella pneumoniae but can be detected in other organisms
Confers resistance to ampicillin and 1GC (exception is cephalexin)
* Susceptible to 2GC, 3GC and 4GC
* Inhibited by clavulanic acid, tazobactam, sulbactam, avibactam, vaborbactam
R to only AMP disc= production of what, a query …
Resistance to only the ampicillin disc indicates the production of a penicillinase ? TEM1, TEM 2, SHV1
What are ESBL’s?
where were they first detected?
are they plasmid or chromosomal borne?
what are its enzymes susceptible to?
extended spectrum b-lactamases are enzymes that encode resistance to:the penicillins,cephalosporins(1GC,
2GC) including the extended-spectrum cephalosporins (3GC AND 4GC) and aztreonam
Klebsiella , Germany 1983
Plasmid borne (can be transferred to other organisms for genetic resistance)
These enzymes are susceptible to the b-lactam inhibitors:
* Clavulanic acid* Tazobactam* Sulbactam
* Avibactam* Vaborbactam* ? Durlobactam
what are some types of esbls
how is it mediated and what is it susceptible to?
which carbapenams can we use to treat them
Some ESBL’s are genetic point mutations of TEM-1 or TEM-2 and SHV-1
Other ESBLs include the CTX-M family (160+) – more common than TEM/SHV- Plasmid acquired resistance from chromosomal genes of Kluyvera species
Some OXA enzymes (usually found in GPC, AA mutation in enzyme provides ESBL)
Predominantly plasmid mediated with constitutive expression (NOT chromosomal)
* All are susceptible to Augmentin (AMC) – amoxycillin + clavulanic acid
Can also treat ESBL producing organisms with carbapenems
- The following are used in Australia (all IV)
- Meropenem (MEM)
- Ertapenem (ETP)
- Doripenem (DOR)
- Imipenem is not prescribed in Aust. – due to CSF problems
community isolates usually Susceptible to:
- Amoxycillin/Clavulanate (Augmentin)
- Cephalosporins
Resistance typically to :
- Ampicillin/Amoxycillin
Multiple antibiotic resistance is readily acquired and common in hospital isolates
- Frequently produce (_______)
Note the _____ effect (synergism) between (AMC and CTX) and (AMC and ATM)
Klebsiella pneumoniae
ESBL, keyhole effect
How do we generally detect ESBL in lab? 2 steps
how can we also test using MIC?
First: detect reduced susceptibility to Extended Spectrum b-lactams (3GC) and/or aztreonam - i.e., either completely R or a borderline zone around these disc(s) - possible resistance to CTX (a 3GC), possible resistance to aztreonam (ATM)
Second : demonstrate inhibition of resistance by an inhibitor such as clavulanic acid – seen as a “keyhole effect” with double disc methods
Can be tested using E-test double ended strips (compare MIC of antimicrobials with/without inhibitor)
- Can be tested using broth dilution in micro titre tray (compare MIC of antimicrobials with/without inhibitor)
Calculation of the number of fold difference
MIC without inhibitor divided by MIC with inhibitor = fold x difference- if greater than 8 fold increase or 3x dilutions= ESBL
How to detect ESBL with microtitre tray?
Wells containing bacterial growth have a cell pellet
* The MIC is the lowest concentration of an antibiotic that has no visible growth (no pellet), usually units are ug/mL (same for e test)
What is AMPC b lactamases?
how are they mediated?
WHat can type 1 cephalosporinases or class c cephalosporinases mediate R to, is induced and inhibited by?
clinically important cephalosporinases encoded on the chromosomes of many of the Enterobacteriaceae and a few other organisms, where they mediate resistance to cephalothin, cefazolin, cefoxitin, most penicillins, and β-lactamase inhibitor-β-lactam combinations
Chromosome OR Plasmid mediated
- Inducible expression when encoded on chromosome (IC)(ESCHAPM group)
- Constitutive expression when encoded on a plasmid (CP)
- Inducible expression encoded by a plasmid is rare
Type 1 cephalosporinases or Class C cephalosporinase
- Can mediate resistance to all b-lactams (Pc’s, 1-2-GC) except 4GC and the carbapenems (depends on organism)
- Can be induced by imipenem (and not meropenem) – hence the use of IMP discs
- Inhibited by aztreonam but not clavulanic acid, tazobactam, sulbactam, avibactam, vaborbactam
What organisms produce AMPC B lactamases? ESCHApPM
E entertobacter (E. cloacae, E. aerogenes)
S serratia marcescens
C citrobacter freundii
H hafnia alvei
A aeromonas (all species except A. sobria, A. veronii) –
designated as ‘A1’ enzyme in Aeromonas
proteus
P providencia (P. stuartii, P. rettgeri)
M morganella morganii
How can we detect an inducible AMPC cephalosporinase?
AMP C enables Resistance to Augmentin (not inhibited by clavulanic acid), while other inducible cephalosporinases are S to AMC
Appears quite resistant (to multiple discs)
IPM disc adjacent to either a cephalosporin or cephamycin disc* Visualise enhanced growth between IPM and the cephalosporin/cephamycin disc into the latter’s zones
May appear S to 3GC on plate, CTX (Cefotaxime) Report results according to genus/guideline
Usually sensitive to 4GC
* CPO (cefpirome)
* FEP (cefepime)
How to detect plasmid-mediated AMP C cephalosporinases (constitutive expression)- where have they been found?
what are they inhibited by and what are they R to?
what is it susceptible to?
what happens if it is produced at high levels?
how can it be confirmed?
Plasmid mediated AMP C have been found in: - Escherichia coli- Klebsiella pneumoniae- Salmonella sp.
PM AMPC is inhibited by aztreonam and boronic acid and is resistant to AMC
susceptible to cefepime FEP (4th Gen Cephalosporin – 4GC)
If produced at high levels, will be resistant to cefotaxime (3GC) and ceftazidime (3GC)
- Confirmation of a plasmid mediated AMP C is performed using boronic acid
- Use plain paper discs that have been presoaked in boronic acid
How to detect Non-AMP C, inducible cephalosporinases
(Bush Group 2e cephalosporinases)
Not as broad spectrum as an AMP C enzyme
* Susceptible to AMC disc BUT with, inducible production (IPM → CTX)
B lactam R for Gram negs
what does EEC stand for?
What does A1 for aeromonas mean?
Which can be enterobacteriace with ESBL or AMPC?
EEC= Enterobacter aerogenes - Enterobacter cloacae
- Citrobacter freundii
A1= AMPC in aeromonas
Enterobacteriacea w ESBL or AMPC can be Providencia and Hafnia
What are carbapenemases and what are carbapenems?
where were carbapenemases first discovered?
enzymes resistant to Carbapenems – ertapenem, meropenem, imipenem, doripenem which are broad spec useful for GPC, GNB including Pseudomonas, Burkholderia, Stenotrophomonas
Klebsiella pneumonia (KP), called KPC and 4 classes A,B,C,D but is NOT restricted to klebsiella- E. coli, Salmonella,
Wat are 3 reasons why patients in long term care facilities are susceptible to drug resistant infections
acutely ill (20 days in hospital) and require medical devices
- heavy use of antibiotics
- extended time — usually more than 20 days
what is the fatality rate and treatment to KPC
Fatality rate of 47-57%
* Treatment limited to either colistin or tigecycline
- Aztreonam is a possibility Treatment of last resort if completely R is surgery
What class are metallo B lactamases in as carbapenemases
which variants of the NDM are dominant globally?
what are they susceptible to?
Metallo β-lactamases that belong to the Class B1 carbapenemases
- NDM-1, NDM-4, NDM-5, and NDM-7 are dominant globally
Only susceptible to polymyxins (colistin), tigecycline and possibly aztreonam
How to detect Metallo B lactamase enzymes (includes NDM1-32)
enzyme relys on zinc ion to function
susceptibility plate need IPM or MEM indicating resistance
Confirm class B enzymes using EDTA discs
- EDTA chelates zinc
- Zone of NG where enzyme is inhibited by EDTA
Aztreonam maybe useful as long as the
organism does not possess any other concurrent β-lactamases i.e., report the susceptibility as it appears
* Also test tigecycline and colistin
* The Rosco kit from the previous slides can also detect MBLs
EDTA allows antibiotics to work to inhibit growth
What is a fully S strain of s aureus?
Only resistant to Benzylpenicillin (P0.5) is a;so a strain reasonably common
one that is susceptible to penicillins- v rare now
Resistant FOX = methicillin resistant = Resistance to all β-lactams
MRSA are also resistant to all the β-lactam inhibitors
Vancomycin is the drug of choice for MRSAs
only r to penicillin- but Inhibited by clavulanic acid and tazobactam (possible ESBL keyhole pattern)
* Chromosomal and plasmid mediated in staphylococci
what is oxacillin OX a surrogate for?
Oxacillin (OX) is also a surrogate for methicillin resistance in CoNS (CDS)
- Both FOX and OX are put on a plate when the ID is not known
- Susceptible = methicillin susceptible
- Resistant = methicillin resistant
MRSA mec Genotype and Phenotype
mecA phenotype = R to oxacillin, R to Cefoxitin
* mecC phenotype = S to oxacillin, R to Cefoxitin
When do we check for Inducible Resistance to Clindamycin?
Applies to staphylococci and β-haemolytic streptococci (not enterococci)
* If D test is positive ,report R to DA.If isolate is D test negative ,report S for DA
