Direct Damage a. Some microbes secrete enzymes which break down cells or break down the material between cells. Toxins can damage cell membranes, inhibit enzymes, disrupt the nervous system, or destroy blood cells or vessels. Exotoxins - substances that are synthesized internally and secreted into the surrounding medium. Most are proteins, many of which are enzymes.
Many exotoxins are the most lethal substances known.
1 mg of the exotoxin botulinum will kill 1 million guinea pigs. Endotoxins - usually part of the cell wall. Endotoxins are produced by many Gram negative bacteria. The toxin itself is a lipid, called lipid A, located on the outer membrane of the cell wall. Probably due to lysogenic viruses.