Extended-spectrum β-lactamases: Difference between revisions

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== Background ==
==Background==


* 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]]
*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]]
* This definition excludes AmpC (which hydrolyze [[cephamycins]]) and carbapenemases (which hydrolyze [[carbapenems]])
*This definition excludes AmpC (which hydrolyze [[cephamycins]]) and carbapenemases (which hydrolyze [[carbapenems]])
* Includes primarily Ambler Class A β-lactamases
*Includes primarily Ambler Class A β-lactamases


=== Identification ===
===Identification===


* ESBLs are screened for by identifying organisms with increased MICs to one or more third-generation [[Cephalosporins|cephalosporin]] or [[Monobactams|monobactam]]
*ESBLs are screened for by identifying organisms with increased MICs to one or more third-generation [[Cephalosporins|cephalosporin]] or [[Monobactams|monobactam]]
** CLSI uses [[cefpodoxime]], [[ceftazidime]], [[aztreonam]], [[cefotaxime]], or [[ceftriaxone]]
**CLSI uses [[cefpodoxime]], [[ceftazidime]], [[aztreonam]], [[cefotaxime]], or [[ceftriaxone]]


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*Organisms that screen positive have further testing to determine the presence of an ESBL
* For organisms that screen positive, they are then tested for third-generation [[Cephalosporins|cephalosporin]] resistance that is attenuated by [[clavulanic acid]]
*'''Class A''', for all organisms that screen positive,
** CLSI uses either [[ceftazidime]] or [[cefotaxime]], with and without [[clavulanic acid]]
**A double-disc diffusion method is used to assess whether the third-generation [[Cephalosporins|cephalosporin]] resistance that is attenuated by [[clavulanic acid]]
** An increase in the zone of ≥5 mm is diagnostic of ESBL production
**CLSI uses either [[ceftazidime]] or [[cefotaxime]], with and without [[clavulanic acid]]
**An increase in the zone of ≥5 mm is diagnostic of Class A ESBL production
*'''Class B''', for organisms that are also resistant to [[carbapenems]]
**See [[Carbapenemases]] for details
*'''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 ==

* Carbapenem, with [[meropenem]] or [[imipenem]] preferentially, though [[ertapenem]] can be considered if no septic shock[[Pichia kudriavzevii]]
* In some patients, can consider [[piperacillin-tazobactam]], [[amoxicillin-clavulanic acid]], or [[fluoroquinolones]]
* For non-severe [[UTI]] without septic shock, can consider [[co-trimoxazole]], [[aminoglycosides]], or [[fosfomycin]] (IV)
* See also [[Carbapenem-resistant organisms]]

Latest revision as of 02:22, 14 November 2024

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