As was previously stated by others, antibiotic compounds are produced not
only by fungi, but by bacteria such as members of the genus Streptomyces
and the Genus Bacillus (bacitracin for example), and some are not produced
by living things at all, such is the case with the sulfa drugs. In
discussions concerning these compounds, I tend to classify them as
antimicrobial agents, but make distinctions between antibiotics,
disinfectants, antiseptics, and preservatives. The concept of
"antibiosis" and "antibiotics" arose from the activity displayed by one
life form in the production of compounds used to limit the growth of
potential competitor species (example- the interaction between Penicillium
and the gram positive coccus Staphylococcus aureus), but has been expanded
over time to include any compound or family of compounds either naturally
or artificially produced which inhibit the growth of microorganisms.
Since these agents do not sterilize, their primary function is to reduce
microbial numbers in the body of a host sufficiently to allow the host's
own immune responses to fight the infection.
As to the question concerning lysozyme as an antimicrobial agent, a
previous post was quite correct in defining the activity of this compound
as an agent active against peptidoglycan, particularly true for gram
positive cells. Lysozyme is a nonspecific chemical defense produced by our
body, and should be considered an bacteriostatic antimicrobial, but not a
sterilant or antibiotic. It serves as one of many nonspecific mechanisms
(not to be confused with humoral and cell-mediated specific
defenses) produced in the layered defense the body has against infection.
While I am unaware of antibiotic compounds produced directly by the
mammalian body, the normal microflora in and on that body do provide their
own defenses against opportunistic agents of infection, either by simple
competitive exclusion, or via the production of chemical agents which
either directly (agents produced by some E. coli to inhibit the growth of
other stains) or indirectly (acid by-products of metabolism,
such as those produced by lactobacilli) limit the growth of competitors.
I hope this helps a bit,
Karl J. Roberts, Ph.D.
