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