There are other membrane damaging toxins as
well, lipases for example, enzymes that digest
lipids, an example is the lecithinase from
Clostridial species. This enzyme can lyse
cells and eliminate defenses and provides
nutrients for bacteria. These are bacterial
toxins lysing eukaryotic cells to avoid defenses
and the lyse cells produce nutrients for the
bacteria. Hemolysins can lyse red and white
blood cells, and then there are toxins that
form pores in the cell membrane, they insert
into the membrane and they allow water to
flow in and the cell bursts, again a way for
bacteria to avoid some of those immune cells
that are trying to get rid of the bacteria.
We also have what are called heterogeneous
pore-forming toxins, these are produced by
a variety of bacteria, one well-known one
is Streptolysin O, produced by the Streptococci.
This pore-forming toxin binds cholesterol
and damages liposomes in cells of the host,
causes the cells to lyse, part of the reason
why tissues are damaged. Another set of toxins
that are produced and if you're thinking,
“boy, bacteria make a lot of toxins”,
you are right, this is their modus operandus.
These are called extracellular matrix toxins.
The extracellular matrix is the area between
cells. Here on this picture, we are showing
two cells and the area between them and below
them, this is filled with all kinds of substances
that provide protection and hold the cell
together, this is the extracellular matrix.
Bacteria produce enzymes called hyaluronidase.
Hyaluronic acid is a component of the extracellular
matrix, as you can see here, and this breaks
it down. It breaks down connective tissue
allowing bacteria to spread better. Streptokinase
is an enzyme produced by streptococci, it
activates plasminogen, converts it to plasmin,
which then attacks blood clots and gets them
to dissolve. Bacteria don't like blood clots
because it inhibits them from moving about,
it may restrict them, so this enzyme takes
care of that; and finally collagenases and
elastases also digest the extracellular matrix
allowing free flow movement of the bacteria.