Researchers have identified a novel chloramphenicol acetyltransferase gene, designated CatB14, in Riemerella anatipestifer and propose a reclassification of the entire type B CAT family. The study appeared in Veterinary Microbiology on 10 October 2026.

The work comes from a large team at the avian disease research groups of Sichuan Agricultural University — Nianjia He, Zhishuang Yang, Mingshu Wang, Renyong Jia, Shun Chen, Mafeng Liu and colleagues, with senior authors Anchun Cheng and Dekang Zhu.

Why does this matter at the exam table?

Riemerella anatipestifer is a major bacterial pathogen of ducks, causing serositis in waterfowl flocks. Chloramphenicol acetyltransferases, or CAT enzymes, inactivate chloramphenicol-type drugs by acetylating them. When a bacterium carries a functional CAT gene, phenicol antibiotics lose their activity against that isolate.

A new CAT gene in this pathogen signals two practical consequences for poultry and waterfowl practitioners:

• Phenicol susceptibility results for R. anatipestifer isolates may not reflect the true resistance mechanism unless laboratories account for CAT-family genes.
• Resistance determinants circulating in duck flocks add to the pool of mobilizable chloramphenicol-resistance elements in food-animal production.

What does reclassification of the type B CAT family change?

The type B CAT family groups enzymes that share structure and substrate behavior. By identifying CatB14 in R. anatipestifer, the authors found the existing family framework inadequate to capture the diversity of these enzymes. Their reclassification proposal would redefine how type B CATs are grouped and named.

For diagnostic laboratories and surveillance programs, a revised nomenclature matters directly. Correct classification of a resistance gene determines:

• which sequences database searches should flag as phenicol-resistance determinants;
• how epidemiological surveillance tracks the spread of CAT genes between bacterial species;
• whether molecular assays targeting known CAT variants detect emerging ones.

What are the companion-animal, food-animal and public-health implications?

Companion animals. The study addresses a waterfowl pathogen, so the direct relevance to small-animal practice is limited. However, CAT genes transfer between bacterial species, and chloramphenicol-family drugs remain in veterinary use in some markets under specific regulatory controls.

Food animals. R. anatipestifer affects primarily ducks and other waterfowl, a production sector where antibiotic options are narrower than in chickens. A new resistance gene narrows them further. Practitioners serving duck operations should rely on culture and susceptibility testing rather than empirical phenicol use.

Public health. Chloramphenicol is a critically regulated antibiotic in human medicine. FDA CVM prohibits chloramphenicol use in food-producing animals in the United States, and the EMA classifies it as a highest-priority critically important antimicrobial. Any expansion of CAT-mediated resistance in production environments warrants surveillance attention, because acetyltransferase genes often reside on mobile elements capable of crossing species boundaries.

What happens next?

The identification of CatB14 in R. anatipestifer gives diagnostic developers and surveillance networks a new target sequence to incorporate, and the proposed reclassification of the type B CAT family invites database curators and reference laboratories to update their gene nomenclature as the findings circulate.