CORE-ABR
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Resistance gene

Class A beta-lactamase (CTX-M)

Predicts: Extended-spectrum beta-lactamase (ESBL) production. Reported qualitatively as detected or not detected.

Qualitative PCR targetApplied per organism

Mechanism

A serine beta-lactamase that hydrolyzes penicillins and third-generation cephalosporins.

What it removes from the grid

Penicillins, and first- through third-generation cephalosporins including ceftriaxone.

What it spares

Carbapenems remain active against CTX-M producers, and CTX-M is inhibited by avibactam.

A multiplex panel can't say which organism in a mixed specimen carries a detected gene. CORE-ABR applies Class A beta-lactamase (CTX-M) only to organisms known to carry it, and only to the agents its mechanism defeats — so a detected gene moves the right cells and spares the rest.

Organisms it is applied to

Escherichia coliThe most common cause of urinary tract infection, and a frequent organism in wound and intra-abdominal specimens.Gram-negative bacteria · UTI · WoundKlebsiella pneumoniae / oxytocaCommon uropathogens and a leading host of ESBL and KPC carbapenemase genes.Gram-negative bacteria · UTI · Wound · STIProteus mirabilis / vulgarisUrease-producing Enterobacterales associated with complicated UTI, catheters and stones.Gram-negative bacteria · UTI · WoundEnterobacter aerogenes / cloacaeEnterobacterales with chromosomal AmpC. E. aerogenes has been renamed Klebsiella aerogenes; many panels still report the…Gram-negative bacteria · UTI · Wound · STICitrobacter freundiiAn Enterobacterales species that carries a chromosomal AmpC beta-lactamase.Gram-negative bacteria · UTI · Wound · STIAcinetobacter baumanniiA non-fermenting gram-negative bacillus, notorious in healthcare settings for accumulating resistance.Gram-negative bacteria · UTI · Wound · STI

Coding

Z16.12 (extended spectrum beta lactamase resistance), as documentation supports. CORE-ABR adds resistance findings as supporting codes, not primary, and prints the rationale on the report.

Tagged

Decision support only. The treating clinician decides. Molecular genotype does not replace phenotypic susceptibility testing, culture, or public-health reporting. Absence of a detected resistance gene does not establish susceptibility. Organism targets vary by panel; CORE-ABR is configured to the assay each laboratory runs.