Bacteria cells are all around us. They cause disease and are essential for human life. Although several bacteria such as Streptococcus pneumoniae and Escherichia coli live symbiotically within human bodies, the bacteria structure and function is very different than human cells. Bacteria metabolize and produce some of the nutrients and ions that humans can't process, such as nitrogen and vitamin K. Bacteria cell structure might be different, but they have mutated over eons to survive environmental changes and reproduce.
Bacteria are prokaryotic cells that are distinguished from human, eukaryotic cells. The main difference between these two cell types is how internal organelles, a specialized subunit of a cell, are organized. Prokaryotic cells do not have membrane-bound organelles. They also have no nucleus that contains DNA, and their DNA is one, circular molecule instead of separate chromosomes like a eukaryotic cell.
One of bacteria cells' virulence factors is its capsule. The capsule is made of a thick layer of polysaccharide material. The goal of the capsule is to protect it from drying out, and it provides protection against phagocytosis from immune cells. Capsules are virulence factors for bacteria such as S. pneumoniae and E. coli. Without this capsule, bacteria of this type are avirulent and do not cause disease.
Bacteria have cell walls made of a peptidoglycan layer that makes the cell rigid and gives it shape. It also serves as an anchor for the pili and flagella. It helps contain the organelles and keeps the cell from bursting under large changes from osmotic pressure. Cell walls are used by scientists to distinguish and categorize bacteria through gram-staining procedures.
Many bacteria have pili, which are tiny hair-like structures that branch out from the cell wall. These structures have two purposes. Pili are a part of a bacterium's virulence factors. They attach to host tissue and cells giving them the ability to cause infection. Additionally, special pili are used by bacteria for conjugation, a process in which one bacterium sends genes such as antibiotic resistance to neighboring bacteria cells.
Flagella are also hair-like structures similar to pili, but flagella are used for locomotion by the bacteria cell. They are on one end of the bacteria, at both ends, or sometimes they surround the entire cell. Flagella help the bacteria move away from toxic chemicals or move toward nutrients. They work in a propeller-type movement, spinning around to move the bacteria to a location.