Extended-spectrum β-lactamases: Difference between revisions

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==Background==
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#REDIRECT [[Β-lactamases]]
  
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*Extended-spectrum β-lactamases (ESBLs) are generally defined as [[β-lactamases]] that hydrolyze [[penicillins]], first-, second-, and third-generation [[cephalosporins]], and [[aztreonam]], but not [[cephamycins]] or [[carbapenems]]
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*This definition excludes AmpC (which hydrolyze [[cephamycins]]) and carbapenemases (which hydrolyze [[carbapenems]])
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*Includes primarily Ambler Class A β-lactamases
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===Identification===
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*ESBLs are screened for by identifying organisms with increased MICs to one or more third-generation [[Cephalosporins|cephalosporin]] or [[Monobactams|monobactam]]
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**CLSI uses [[cefpodoxime]], [[ceftazidime]], [[aztreonam]], [[cefotaxime]], or [[ceftriaxone]]
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{| class="wikitable"
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|+Screening for ESBL production
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!Bacterium
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!Antibiotic
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!Disc Diffusion
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!Broth Microdilution
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|-
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| rowspan="5" |[[Klebsiella pneumoniae]], [[Klebsiella oxytoca]], and [[Escherichia coli]]
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|[[cefpodoxime]]
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|≤17 mm
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|≥8 μg/mL
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|-
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|[[ceftazidime]]
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|≤22 mm
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|≥2 μg/mL
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|-
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|[[aztreonam]]
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|≤27 mm
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|≥2 μg/mL
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|-
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|[[cefotaxime]]
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|≤27 mm
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|≥2 μg/mL
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|-
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|[[ceftriaxone]]
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|≤25 mm
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|≥2 μg/mL
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|-
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| rowspan="3" |[[Proteus mirabilis]]
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|[[cefpodoxime]]
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|≤22 mm
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|≥2 μg/mL
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|-
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|[[ceftazidime]]
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|≤22 mm
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|≥2 μg/mL
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|-
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|[[cefotaxime]]
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|≤27 mm
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|≥2 μg/mL
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|}
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*Organisms that screen positive have further testing to determine the presence of an ESBL
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*'''Class A''', for all organisms that screen positive,
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**A double-disc diffusion method is used to assess whether the third-generation [[Cephalosporins|cephalosporin]] resistance that is attenuated by [[clavulanic acid]]
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**CLSI uses either [[ceftazidime]] or [[cefotaxime]], with and without [[clavulanic acid]]
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**An increase in the zone of ≥5 mm is diagnostic of Class A ESBL production
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*'''Class B''', for organisms that are also resistant to [[carbapenems]]
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**See [[Carbapenemases]] for details
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*'''Class C''', for organisms that are non-susceptible to [[cefoxitin]]
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**A double-disc diffusion method is used to test if the results for [[cefoxitin]] are attenuated by [[cloxacillin]] (that is, if the isolate becomes even more susceptible)
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**An increase in the zone of ≥4 mm is positive for AmpC (Class C ESBL) phenotype
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*'''Class D''', difficult to identify with phenotypic testing
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== Management ==
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* See also [[Carbapenem-resistant organisms]]

Latest revision as of 12:09, 2 April 2022

Background

Identification

Screening for ESBL production
Bacterium Antibiotic Disc Diffusion Broth Microdilution
Klebsiella pneumoniae, Klebsiella oxytoca, and Escherichia coli cefpodoxime ≤17 mm ≥8 μg/mL
ceftazidime ≤22 mm ≥2 μg/mL
aztreonam ≤27 mm ≥2 μg/mL
cefotaxime ≤27 mm ≥2 μg/mL
ceftriaxone ≤25 mm ≥2 μg/mL
Proteus mirabilis cefpodoxime ≤22 mm ≥2 μg/mL
ceftazidime ≤22 mm ≥2 μg/mL
cefotaxime ≤27 mm ≥2 μg/mL
  • Organisms that screen positive have further testing to determine the presence of an ESBL
  • Class A, for all organisms that screen positive,
  • Class B, for organisms that are also resistant to carbapenems
  • Class C, for organisms that are non-susceptible to cefoxitin
    • A double-disc diffusion method is used to test if the results for cefoxitin are attenuated by cloxacillin (that is, if the isolate becomes even more susceptible)
    • An increase in the zone of ≥4 mm is positive for AmpC (Class C ESBL) phenotype
  • Class D, difficult to identify with phenotypic testing

Management

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