Microbiology

Microbiology is the study of organisms that are too small to be clearly seen by the unaided eye. It includes five major groups of microorganisms: the subdivisions of virology, bacteriology, mycology, phycology and protozoology. The cell wall determines the shape of the bacteria. Some bacteria can survive without a cell wall. The mycoplasma is the smallest known bacteria to survive outside living cells, and they do not have a constant shape, i.e. they are pleomorphic.

The cell membrane of the bacteria is differentially permeable, and is also the site where enzymes occur, sited on the mesosomes. Endospores are round or oval bodies, formed inside the bacterial cell in adverse conditions to help the bacteria survive. Endospores may remain viable for many years through adverse conditions, but as conditions improve the endospore will germinate and produce a new bacterial cell. Sterilisation is the process of destroying all forms of microbial life, including spores. It is absolute, and there are no degrees of sterilization. Disinfection is the process of destroying vegetative pathogens, but not necessarily endospores or viruses. Disinfectants tend to reduce or inhibit microbial growth, but normally do not sterilize. Gram positive organisms are more susceptible to disinfectants and antiseptics than Gram negative organisms. Pseudomonas are resistant to chemical agents, and will actively grow in some disinfectants and antiseptics.

Many organisms inhabit the body without causing us any harm, and in some cases are positively beneficial and essential for health. Mutuals are bacteria which actually aid some process in the body, such as vitamin K-producing bacteria in the gut. Commensals benefit from living on the body, but we gain no benefit directly from their presence. There are certain conditions in which normal flora may cause infection such as taking broad spectrum antibiotics, reduced immunity , debility, stress. There are three common types of skin infections: Cellulitis, Erysipelas, and Impetigo (Pyoderma). 

Cellulitis is usually an easily treated, but potentially dangerous skin infection. Cellulitis sometimes results when a cut, scrape, insect bite, splinter, or other break in the skin allows bacteria to enter underlying tissues. Often, lymph nodes close to the affected skin will be enlarged, and there may be red streaks running through the skin away from the infection.

Erysipelas is a form of cellulitis that affects only the top layers of the skin. It is more common among children and the elderly. Erysipelas differs from cellulitis in that the inflamed area is distinct from surrounding skin-it is raised, firm, and the redness is sharply marked off. 

Impetigo (pyoderma) is the most common bacterial infection of the skin. It is contagious and can happen at any age, but is most common in young children. Impetigo appears in the form of reddish sores that blister to produce a yellow-brown fluid.