Drugs active against essentially all Gram-negative (and other) anaerobes are , , , and combinations of β-lactam drugs plus a β-lactamase inhibitor.

Antibiotic resistance among anaerobes has steadily increased since the early 1970s. The most frequently isolated antibiotic-resistant anaerobe is Bacteroides fragilis.

Other isolates have less predictable patterns, and certain anaerobes (some Clostridium, Fusobacterium, and Prevotella species, for example) may be - resistant due to β-lactamase. Isolates with a positive β-lactamase test should be considered resistant to and .

Resistance to the tetracyclines, the penicillins, , and other antibiotics has emerged among strains of Bacteroides, Clostridium, and anaerobic cocci. Genetic transfer of antibiotic resistance has been documented in anaerobic environments.

Other types of resistance encountered in anaerobic bacteria include inactivating enzymes such as acetyltransferase, plasmid-mediated transferable multiple-drug resistance, changes in porin molecules in the outer membrane of the bacterial cell, decreased uptake of drug by other mechanisms, changes in the ...

Antimicrobial resistance happens when germs like bacteria and fungi develop the ability to defeat the drugs designed to kill them. Resistant infections can be difficult, and sometimes impossible, to treat. Antimicrobial resistance is a naturally occurring process.

Anaerobic bacteria known to be resistant to include occasional anaerobic cocci, some nonsporulating gram-positive bacilli and propionibacterium.