Cephamycins are a group of beta-lactam antibiotic

Beta-lactam antibiotic

β-Lactam antibiotics are a broad class of antibiotics, consisting of all antibiotic agents that contains a β-lactam nucleus in its molecular structure. This includes penicillin derivatives , cephalosporins , monobactams, and carbapenems...

s. They are very similar to cephalosporin

Cephalosporin

The cephalosporins are a class of β-lactam antibiotics originally derived from Acremonium, which was previously known as "Cephalosporium".Together with cephamycins they constitute a subgroup of β-lactam antibiotics called cephems.-Medical use:...

s, and the cephamycins are sometimes classified as cephalosporins.

Like cephalosporins, cephamycins are based upon the cephem

Cephem

Cephems are a sub-group of beta-lactam antibiotics including cephalosporins and cephamycins....

 nucleus (O-methylated cepham nucleus). Unlike most cephalosporins, cephamycins are a very efficacious antibiotic against anaerobic microbes.

Cephamycins were originally produced by Streptomyces

Streptomyces

Streptomyces is the largest genus of Actinobacteria and the type genus of the family Streptomycetaceae. Over 500 species of Streptomyces bacteria have been described. As with the other Actinobacteria, streptomycetes are gram-positive, and have genomes with high guanine and cytosine content...

, but synthetic ones have been produced as well.

Cephamycins possess a methoxy group at the 7-alpha position.