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The Collaborative International Dictionary of English v.0.48 (gcide)

Lactam \Lac"tam\, n. [Lactone amido.] (Chem.)
One of a series of anhydrides of an amido type, analogous to
the lactones, as oxindol; a cyclic amide.
[1913 Webster]

{beta-lactam} or {[beta]-lactam},
(a) a lactam in which the amide bond is contained within a
four-membered ring, which includes the amide nitrogen and
the carbonyl carbon.
(b) an antibiotic containing a beta-lactam, such as a
{penicillin}, {cephalosporin}, or {carbapenem}; also
called a {beta-lactam antibiotic}. [informal, laboratory
slang]
[PJC]


Cephalosporin \Ceph"a*lo*spor`in\
(s[e^]f"[.a]*l[-o]*sp[=o]r`[i^]n), n. [from Cephalosporium, a
fungus producing the first of the series discovered.] (Chem.)
any of a class of chemical substances, some of which have
therapeutically useful antibacterial activity, whose
structure contains a beta-lactam ring fused to a six-membered
ring containing a sulfur and a nitrogen atom. The first of
the series, {cephalosporin C}, was discovered by G. Brotzu in
1955 in the culture broth of a {Cephalosporium} species found
off the coast of Sardinia. Other cephalosporins have been
found to be produced by species of soil bacteria
(actinomycetes). Many semisynthetic analogs have been tested
for antibacterial effect, and several of them have found use
as important clinically useful antibacterial agents, some of
which may be taken orally for treatment of bacterial
infections. The cephalosporins are the second class of
beta-lactam antibiotic to be discovered, the first being the
{penicillins} and more recent classes being the
{thienamycins} and {sulfazecins}. The {cephamycins} are a
variant of cephalosporins with a methoxyl group on the
beta-lactam ring, rendering them more resistant to
penicillinases. Among the cephalosporins which have been
found clinically useful are {cephalexin}, {cephaloridine},
and {cephalothin}.
[PJC]

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