Beta-lactamases in anaerobic, intestinal bacteria: a narrative review

Anaerobic bacteria in the human intestinal microbiota play a pivotal role in antibiotic resistance, primarily through the production of beta-lactamases. This narrative review explores the diversity of beta-lactamases found in intestinal anaerobes, their functional characteristics, and clinical implications. Species of the genus Bacteroides are major producers, harboring enzymes from Ambler classes A (e.g. CepA, CfxA and CblA), B (e.g. CfiA and CcrA) and D (e.g. OXA-347), with activity ranging from cephalosporinases to carbapenemases and oxacillinases. Other gut members, including Clostridioides difficile, Fusobacterium nucleatum, and Acidaminococcus fermentans, also encode specific beta-lactamases. These enzymes contribute to microbiota resilience following beta-lactam exposure and can protect neighboring bacteria via extracellular degradation. This protective mechanism has inspired therapeutic applications, such as recombinant beta-lactamases (ribaxamase, SYN-006) designed to preserve gut integrity during antibiotic therapy. Understanding these intrinsic resistance mechanisms is essential for optimizing antibiotic stewardship and mitigating the spread of resistance genes. Copyright © 2026. Published by Elsevier Ltd.