Bacteria are single cellular prokaryotes. This means they lack a nucleus and their genetic information is typically in a circular form free floating in the cytoplasm. Most bacteria have cell wall comprised of a peptidoglycan which is essential for their survival. Becuase of their simple structure and small size bacteria are able to reprouce at astonishing rates
The cell wall is essential to the survival of many bacteria, and the antibiotic penicillin is able to kill bacteria by inhibiting a step in the synthesis of peptidoglycan.
How do bacteria make us "sick"
As you may have heard before, bacterial cells outnumber human body cells 10 to 1. Fortunately nearly all of those cells either have no effect on you or actually benefit you in some way. Very few bacterial cells actually cause us disease, but those that do can wreak havoc on our bodies.
Bacterial cells can either be Gram-positive or Gram-negative based on the structure of their cell wall. Gram-negative bacteria release endotoxins, and they can act as pyrogens (fever causing molecules)
Both gram-postive and gram negative bacteria release Exotoxins, or protein toxins. Exotoxins are grouped into categories based on their biologic effect on cells: Cytotoxins kill or damage cells, neurotoxins interfere with nerve impulses and enterotoxins affect the intestines.
Many well-known disease symptoms are traced back to exotoxins secreted by various bacteria. For example, the Gram-positive bacterium Streptococcus pyogenes releases three cytotoxins — one of its toxins damages blood capillaries, causing the infamous red rash of scarlet fever. Clostridium perfringens releases a toxin that disrupts normal cellular function and leads to the mass tissue necrosis (death) commonly known as gangrene.