Amp C

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Amp C

  1. 1. Detection of plasmid-mediated class C β -lactamases Doi Y, Paterson DL International Journal of Infectious Diseases (May 2007) 11, 191-197 Dr Preneshni R Naicker
  2. 2. Introduction <ul><li>Β -lactamases are produced as a means of self-defense </li></ul><ul><li>4 Molecular classes </li></ul><ul><li>Methods to screen for and confirm ESBLs and MBLs are established </li></ul>
  3. 3. <ul><li>ESBLs </li></ul><ul><li>Screen for ↓ susceptibility to C3G or Aztreonam </li></ul><ul><li>Confirm: presence of an inhibitory effect of clavulanic acid against the antimicrobial activity of CAZ and CTX </li></ul>
  4. 4. <ul><li>MBLs </li></ul><ul><li>Mercaptoacetic acid or EDTA – tested against CAZ or IMI </li></ul><ul><li>Class C </li></ul><ul><li>?not well established </li></ul><ul><li>Lack of simple & reliable detection method </li></ul>
  5. 5. Class C β -lactamases <ul><li>Genes used to be confined to the chromosome of various gram – species as AmpC, have disseminated on plasmids </li></ul><ul><li>Bacteria R to most β -lactams including cephamycins and β -lactam/ β -lactamase inhibitor combinations. </li></ul>
  6. 6. Table 1. Rationale for detection of plasmid-mediated class C β-lactamases <ul><li>Increasing prevalence in the USA and probably worldwide (paucity of data on prevalence outside the USA) </li></ul><ul><li>Infection control opportunities for prevention of spread of important mechanisms of plasmid-mediated multi-drug resistance </li></ul><ul><li>Potential treatment failure with broad-spectrum cephalosporins since laboratories may report plasmid-mediated class C producers as susceptible to broad-spectrum cephalosporins using conventional CLSI breakpoints </li></ul><ul><li>Plasmid-mediated class C producers may appear susceptible using conventional CLSI breakpoints yet meet CLSI screening breakpoints for ESBLs. Since they will be negative by phenotypic confirmatory tests for ESBLs, they will be erroneously reported as susceptible to broad-spectrum cephalosporins </li></ul><ul><li>CLSI, Clinical and Laboratory Standards Institute; ESBL, extended-spectrum β-lactamases. </li></ul>
  7. 7. Screening Tests for detection of plasmid-mediated class C beta-lactamases <ul><li>Poorly sensitive & specific </li></ul><ul><li>May miss co-production of ESBLs </li></ul>↓ susceptibility to expanded-spectrum cephalosporins but S Cefepime/Cefpirome <ul><li>Highly sensitive but nonspecific </li></ul><ul><li>May represent prodxn of Class B/D/IRT/↑ESBL </li></ul>↓ susceptibility to expanded-spectrum cephalosporins and lack of inhibition of β -lactamase inhibitors <ul><li>Highly Sensitive but Nonspecific </li></ul><ul><li>May rule in strains with ↓ outer mem prodxn/ampC hyperproducers in E.coli </li></ul>↓ susceptibility to expanded-spectrum cephalosporins and resistance to FOX Characteristics Tests
  8. 8. Confirmatory Tests for detection of plasmid-mediated class C beta-lactamases <ul><li>Able to differentiate plasmid borne from chromosomal </li></ul><ul><li>Limited availablility </li></ul>Multiplex PCR <ul><li>Improved sensitivity when combined with clavulanic acid </li></ul>Boronic acid disk test <ul><li>Easy to perform </li></ul><ul><li>Incorp into Automated systems </li></ul>APB-based disk/microdilution test <ul><li>Easier to perform but more complicated </li></ul>AmpC disk test <ul><li>First Phenotypic confirmatory test </li></ul><ul><li>Technically demanding </li></ul>3D Test Characteristics Test
  9. 9. Three-dimensional Test
  10. 10. AmpC Disk Test
  11. 11. Inhibitor-based tests <ul><li>BZBTH2B </li></ul><ul><li>≥ 5mm zone size </li></ul><ul><li>FOX-BA and/or CTT-BA versus FOX and/or CTT alone </li></ul><ul><li>CAZ-CA-BA and/or CTX-CA-BA versus CAZ-BA and/or CTX-BA </li></ul><ul><li>APB </li></ul>
  12. 13. Genetic/Immunologic Tests <ul><li>Multiplex PCR </li></ul><ul><li>ELISA </li></ul>
  13. 14. <ul><li>Thank You </li></ul>

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