Transcript Carbapenems

ANTIMICROBIAL RESISTANCE
9.21.12
Site of Action of antibiotics
• Inhibition of nucleic acid synthesis (Rifampin; quinilones)
• Inhibition of protein synthesis (Tetracyclines;
Chloramphenicol, macrolides, clindamycin,
aminoglycosides, linezolid)
• Action on cell membrane (Polyenes; Polymyxin)
• Interference with enzyme system (Trimethoprim,
Sulphamethoxazole)
• Action on cell wall (Penicillin; cephalosporins, Vancomycin,
carbapenams)
Mechanisms of Drug Resistance
• Change in drug target
• Production of an enzyme that modifies or inactivates the
agent
• Reduced accumulation of the agent
• Limited uptake
• Active Efflux
• Loss of a pathway involved in drug activation
Mechanisms of Drug Resistance
Mechanisms of Drug Resistance
Mechanisms of Gram-Negative Bacterial
Resistance to Antibiotics
Antibiotic Class
Cephalosporins
Mechanism of Resistance
 ESBLs
 chromosomal
cephalosporinases
-Lactamase
inhibitors
 hyperproducers
of -lactamases
 new -lactamases resistant to inhibitors
 chromosomal cephalosporinases
Carbapenems
 porin
Fluoroquinolones
 alterations
mutations
 efflux pump overproduction (excluding imipenem)
 zinc metalloenzymes and other -lactamases
in DNA topoisomerase
 efflux mechanisms
 permeability changes
Campaign to Prevent Antimicrobial Resistance in Healthcare Settings
Selection for antimicrobial-resistant
Strains
Resistant Strains
Rare
Antimicrobial
Exposure
Resistant Strains
Dominant
Target Alterations
• PBPs: in cell membrane
• S. pneumoniae, MRSA
• Intrinsic resistance, enterococci, gonococci, H. infl
• D-Ala-D-Ala target: VRE
• VanA, VanB, VanC, VanD
• Alterations in ribosomes
• Cell membrane changes
Protein Binding Proteins
• Target for all B-lactams
• found as both membrane-bound and cytoplasmic
proteins
• all involved in the final stages of the synthesis of
peptidoglycan, which is the major component of
bacterial cell walls
• More common R mechanism for gram positive
organisms
• Gram neg access to PBP is limited by outer membrane
and thus other mechanisms supersede the binding to this
target
Enzyme Production
• Aminoglycoside modifying enzymes
• B-lactamases:
• Four structural classes:
• Class A: R of S aureus to penicillin, R of E coli to ampicillin and
cephalothin –plasmid mediated
• Class B: hydrolyze carbapenmens/pens/cephs -chromosomal
• Class C: chromosomal, active against cephalosporins
• Class D: plamid mediatated
• ESBL: K. pneumoniae, E. coli : Derived from transfer of
chromosomal genes for inducible amp C onto plasmids
B-lactamase
B-lactame ring
Cefipime
Increased stability to B-lactamase
Increased penetration into gram-positive
Ceftriaxone
-Lactamases: Overview
• Large, diverse family of enzymes
• Widely dispersed in gram-positive (chromosoaml
and plasmid) and gram-negative pathogens
(plasmid)
• Major mechanism of resistance to -lactams in
gram-negative pathogens
• Wide range of activity: older enzymes hydrolyze
older drugs, new derivatives have evolved for
new drugs
•
•
•
ESBLs
AmpC -lactamases
carbapenemases
-Lactamases
• Major groups for gram-neg
• TEM-wide spread-plasmid and transposon
• Enterobacteriaceae, Pseudomonas aeruginosa, Haemophilus
influenzae, and Neisseria gonorrhoeae
• SHV-1
• Klebsiella pneumoniae (chromosomal) and E. coli (plasmid)
• Confer resistance to penicillins and first/second generation
cephalosporins
-lactamase
1960
TEM-2 SHV
TEM-1
Extended spectrum--lactamase
1980s
Cefotaxime
TEM, SHV
CTX
ESBL-Mediated Resistance
• Contain a number of mutations that allow them to
hydrolyze expanded-spectrum β-lactam antibiotics
• Derived from older antibiotic-hydrolyzing -
lactamase enzymes (TEM-1, TEM-2, SHV-1)
• a single amino acid substitution can give rise to new
ESBLs
• Not as catalytically efficient
• Inhibited by β-lactamase inhibitors
• Susceptible to cefoxitin and cefotetan in vitro only
• 10%–40% of K pneumoniae, E coli express
ESBLs
Rupp ME et al. Drugs. 2003;63:353–365.
CTM-X predominant mechanism
E. Coli predominant organism
Canton, Cur Opin in Micr 2006, Pages 466–475
Coresistances among the Enterobacteriaceae isolates of the different ESBL types.
Morosini M et al. Antimicrob. Agents Chemother.
2006;50:2695-2699
Amp-C
• Confer resistance cephamycins (cefotetan,
cefoxitin) and oxyimino- -lactams (cefotaxime,
ceftriaxone, ceftazidime)
• Chromosomal in SPACE organisms and are
inducible
• Poorly expressed in E. coli and is missing from
klebsiella and salmonella species
• Plasmid mediated on other gram-neg, usually not
inducible
• Not susceptible to inhibitors
AmpC- vs ESBL-Mediated Resistance
• Different phenotypic characteristics
• AmpC type -lactamases typically encoded on
chromosome of gram-negative bacteria, can also
be found on plasmids
• AmpC type -lactamases hydrolyze broad- and
extended-spectrum cephalosporins
• ESBLs—NOT AmpC -lactamases—are inhibited
by -lactamase inhibitors (eg, clavulanic acid)
• AmpC production is less effective on cefipime so
best cephalosporin to test
New CLSI Laboratory Standards
• Previously testing for ESBL was based on high MIC to
oxyimino-beta-lactam substrates (cetriaxone, cefotaxime,
cefipime, cetaz) and susceptibility to inhibitors followed by
a confirmatory test to detect the enzyme
• Low sensitivity when mixed mechanisms at play, ie false positive
results, some attempts to overcome this with cloxacillin-containing
Muller–Hinton agar, which inhibits AmpC activity
• When ESBL present susceptibility changed to resist for penicillins,
cephalosporins and monobactams
• Current practice: MICs were changed
• 1-3 doubling dilutions lower
• No need for confirmation of enzyme
• No change in reporting
Epidemiology of Plasmid AmpC
Enzymes in the United States
• Alvarez et al examined a sample of 752 resistant
K pneumoniae, K oxytoca, and E coli strains from 70 sites
in 25 US states
• Plasmids encoding AmpC-type -lactamase were found
in
• 8.5% K pneumoniae samples
• 6.9% K oxytoca samples
• 4% E coli samples
Carbapenemases
• beta-lactamases with versatile hydrolytic capacities.
• Ability to hydrolyze penicillins, cephalosporins,
monobactams, and carbapenems.
• 2 major groups
• Metallo-b-lactamases (MBLs)
• Major R in pseudomonas, acinetobacter, and enterobacter
• Confer High level of R
• Serine b-lactamases
• Oxacillinases or D b-lactamases (OxaA)
• Not as Diverse
• Found mostly in acinetobacter
• Confer only low level of hydrolytic activity therfore another R is necessary to
raise MIC
• Class A carbapenemases
• Found in pseudomonas and enterobacter, but predominant type is found on a
plasmid in Klebsiella
Mechanisms of Bacterial
Resistance to Fluoroquinolones
• Mutations in DNA gyrase and topoisomerase
• Overexpression of efflux pump system
• Bacterial membrane permeability changes
Mechanisms of Antibiotic Resistance in
Nonfermenters
• P aeruginosa and Acinetobacter often multidrug
resistant1
• Mechanisms of resistance include1,2
• production of ESBLs or AmpC -lactamases
• increased efflux of antibiotic agent
• decreased outer membrane permeability
• DNA gyrase mutations
• aminoglycoside modifying enzymes
Carbapenems: Resistance Issues
• Mechanisms of resistance to carbapenems in
P aeruginosa involve
• loss of OprD protein (initially called D2 porin)
• overproduction of efflux pump system
(MexA-MexB-OprM)
• upregulation of other efflux system may be involved (crossresistance to fluoroquinolones)
• Resistance to meropenem depends on both
• Resistance to imipenem mainly mediated
through loss of OprD
Carbapenems: Resistance Issues
Carbapenem nucleus
Ertapenem
Imipenem
Mutated or
missing
D2 porin
D2 Porin (OprD)
Outer
membrane
Periplasm
Penicillin-binding
proteins (PBPs)
Cytoplasmic
membrane
PBP
1
Courtesy of John Quinn, MD.
PBP
2
PBP
3
PBP
4
PBP
5
Mechanisms of Carbapenem Resistance:
Impermeability
• OprD forms narrow transmembrane channels that
are normally accessible only to carbapenems, not
to other ß-lactams
• Loss of OprD porin is associated with decreased
permeability of carbapenems and increased
carbapenem MICs, whereas other ß-lactams
remain active
Mechanisms of Carbapenem Resistance: Efflux
Systems in P aeruginosa
• Upregulation of MexAB-OprM efflux system
• associated with increased MICs of meropenem, not
imipenem
• Coregulation of MexE-MexF-OprN efflux system
with OprD porin in P aeruginosa
• upregulation of efflux associated with OprD
• associated with increased MICs of fluoroquinolones as
well as carbapenems
• mechanism sometimes selected by fluoroquinolones,
rarely by carbapenems
MRSA
• Methicillin resistance is acquired via Mec A
• mobile chromosomal element called staphylococcal cassette
chromosome (SCCmec)
• SCCmec types I, II, and III and are multidrug resistant-large cassettes
• Health-care associated
• SCCmec type IV and type V not multidrug resistant
• Community associated
MecA
• Encodes penicillin binding protein (PBP) 2a
• Weak affinity for methicillin and all beta-lactams
• Substitutes for the usual PBP 1-3 that have a high affinity for betalactams
• Speculation of origination from CoNS
S. Pneumoniae
• Pencillin
• Decreased affinity to PBP
• Can be overcome with high dose
• Macrolides
• Genetic changes to binding target on ribosome-high
level can not be overcome =erm(B)
• Efflux pump-lower level-may be overcome =mef (A)
• Clindamycin
• Ribosomal methylation changing target erm(B)
S. pneumoniae
• Fluoroquinilones
• Bind to either gyrase or topoisomerase or both
• Resistance from mutations in gyrA or parC
• reduce binding of the drug to the site of activity
• Mutations are step wise
• One mutation and R to cipro and levo
• More than one needed for gemi and moxi
• Tetracyclines
• Proteins are produced that package the drug into vessicles which
are extruded from the cell
Enterococcus
• Intrinsic (chromosomal, naturally occurring) resistance to
• B-lactam
• 10 to 1000 times more drug to inhibit an average Enterococcus than an
average Streptococcus
• Due to penicillinase production and PBP5 production
• Aminogylcosides
• Low level to streptocmycin and gentimicin
• Synergism causes cell wall agent to become bactericidal
• High level to tobramycin
Enterococcus-Intrinsic
• Clindamycin-gene encoding efflux pump
• TMP-SXZ• In vitro appears susceptible but in vitro is resistant
• Can utilize preformed folic acid
• Vancomycin at low levels in some strains
Enterococcus
• Genetic transfer to acquire new resistance
• One mechanism, involving pheromone-responsive
plasmids, causes plasmid transfer between E. faecalis
isolates at a very high frequency .
• Another mechanism involves plasmids that can transfer
among a broad range of species and genera, although
usually at a moderately low frequency .
• A third mechanism (conjugative transposition) involves
transfer of specialized transposons at low frequency but
to a very broad range of different kinds of bacteria .
Conjugative transposons are relatively nonselective in
their host range and are one of the few types of elements
known to have crossed the gram-positive/gram-negative
barrier in naturally occurring clinical isolates and to then
cause resistance in these various hosts
Enterococcus
• Acquired
• High level resistance to amnioglycosides
• Loose synergy ability as well
• High level vancomycin resistance
• Van gene clusters on transposons or plasmids
• Very old, probably initially resulted from pressor from natural glyocpeptides
• Van A is the most common and confers highest level of resistance
• Variable level to linezolid
• Depends on the number of mutations in the 23S rRNA