Extended-spectrum β-lactamases: Difference between revisions
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==Background== |
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#REDIRECT [[Î’-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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* Carbapenem, with [[meropenem]] or [[imipenem]] preferentially, though [[ertapenem]] can be considered if no septic shock[[Pichia kudriavzevii]] |
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* In some patients, can consider [[piperacillin-tazobactam]], [[amoxicillin-clavulanic acid]], or [[fluoroquinolones]] |
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* For non-severe [[UTI]] without septic shock, can consider [[co-trimoxazole]], [[aminoglycosides]], or [[fosfomycin]] (IV) |
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* See also [[Carbapenem-resistant organisms]] |
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Latest revision as of 02:22, 14 November 2024
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
- This definition excludes AmpC (which hydrolyze cephamycins) and carbapenemases (which hydrolyze carbapenems)
- Includes primarily Ambler Class A β-lactamases
Identification
- ESBLs are screened for by identifying organisms with increased MICs to one or more third-generation cephalosporin or monobactam
- CLSI uses cefpodoxime, ceftazidime, aztreonam, cefotaxime, or ceftriaxone
| 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,
- A double-disc diffusion method is used to assess whether the third-generation cephalosporin resistance that is attenuated by clavulanic acid
- 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 shockPichia 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
