Antimicrobial Resistance - PowerPoint PPT Presentation

1 / 41
About This Presentation
Title:

Antimicrobial Resistance

Description:

ANTIMICROBIAL RESISTANCE 9.21.12 * P aeruginosa and Acinetobacter are often resistant to multiple antibiotic agents.1 Resistance can be due to one or more of several ... – PowerPoint PPT presentation

Number of Views:1369
Avg rating:5.0/5.0
Slides: 42
Provided by: hay29
Category:

less

Transcript and Presenter's Notes

Title: Antimicrobial Resistance


1
Antimicrobial Resistance
  • 9.21.12

2
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)

3
(No Transcript)
4
(No Transcript)
5
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

6
Mechanisms of Drug Resistance
7
Mechanisms of Drug Resistance
8
Mechanisms of Gram-Negative Bacterial Resistance
to Antibiotics
Antibiotic Class Mechanism of Resistance
Cephalosporins ESBLs chromosomal cephalosporinases
?-Lactamase inhibitors hyperproducers of ?-lactamases new ?-lactamases resistant to inhibitors chromosomal cephalosporinases
Carbapenems porin mutations efflux pump overproduction (excluding imipenem) zinc metalloenzymes and other ?-lactamases
Fluoroquinolones alterations in DNA topoisomerase efflux mechanisms permeability changes
9
Selection for antimicrobial-resistant Strains
10
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

11
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

12
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

13
B-lactamase
14
B-lactame ring
Cefipime
Increased stability to B-lactamase
Increased penetration into gram-positive
Ceftriaxone
15
?-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

16
?-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

b-lactamase
Extended spectrum-b-lactamase
TEM, SHV
1960 TEM-1
CTX
SHV
1980s Cefotaxime
TEM-2
17
(No Transcript)
18
ESBL-Mediated Resistance
  • Contain a number of mutations that allow them to
    hydrolyze expanded-spectrum ß-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 ß-lactamase inhibitors
  • Susceptible to cefoxitin and cefotetan in vitro
    only
  • 1040 of K pneumoniae, E coli express ESBLs

Rupp ME et al. Drugs. 200363353365.
19
CTM-X predominant mechanism
20
E. Coli predominant organism
Canton, Cur Opin in Micr 2006, Pages 466475
21
Coresistances among the Enterobacteriaceae
isolates of the different ESBL types.
Morosini M et al. Antimicrob. Agents Chemother.
2006502695-2699
22
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

23
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
  • ESBLsNOT AmpC ?-lactamasesare inhibited by
    ?-lactamase inhibitors (eg, clavulanic acid)
  • AmpC production is less effective on cefipime so
    best cephalosporin to test

24
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 MullerHinton
    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

25
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

26
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

27
Mechanisms of Bacterial Resistance to
Fluoroquinolones
  • Mutations in DNA gyrase and topoisomerase
  • Overexpression of efflux pump system
  • Bacterial membrane permeability changes

28
Mechanisms of Antibiotic Resistance in
Nonfermenters
  • P aeruginosa and Acinetobacter often multidrug
    resistant1
  • Mechanisms of resistance include1,2
  • production of ESBLs or AmpC b-lactamases
  • increased efflux of antibiotic agent
  • decreased outer membrane permeability
  • DNA gyrase mutations
  • aminoglycoside modifying enzymes

29
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 (cross-resistance to fluoroquinolones)
  • Resistance to meropenem depends on both
  • Resistance to imipenem mainly mediated through
    loss of OprD

30
Carbapenems Resistance Issues
Carbapenem nucleus
Ertapenem
Imipenem
Mutated or missingD2 porin
D2 Porin (OprD)
Outer membrane
Periplasm
Penicillin-binding proteins (PBPs)
Cytoplasmic membrane
PBP1
PBP2
PBP3
PBP4
PBP5
Courtesy of John Quinn, MD.
31
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

32
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

33
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

34
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 beta-lactams
  • Speculation of origination from CoNS

35
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)

36
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

37
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

38
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

39
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

40
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

41
(No Transcript)
Write a Comment
User Comments (0)
About PowerShow.com