Bacillary infection

Bacteria are microscopic, single-celled organisms. Thousands of different kinds of bacteria live throughout the world. Some live in the environment, and others live on the skin, in the airways, in the mouth, and in the digestive and genitourinary tracts of people and animals. Only a few kinds of bacteria cause disease.

Bacteria are classified in several ways.

One way is by their distinctive shapes. Spherical bacteria are cocci, rod-like bacteria are bacilli, and spiral or helical bacteria are spirochetes.

Another way bacteria are classified is by their color after a particular chemical stain (Gram stain) is applied. Some bacteria stain blue and are called gram-positive, whereas others stain pink and are called gram-negative. Gram-positive and gram-negative bacteria differ in the kinds of infections they produce and in the kinds of antibiotics that are likely to kill them.

Gram-negative bacteria have a unique outer membrane that prevents many drugs from penetrating them, making gram-negative bacteria generally more resistant to antibiotics than are gram-positive bacteria. The outer membrane of gram-negative bacteria is also rich in molecules called lipopolysaccharides. If gram-negative bacteria enter the bloodstream, their lipopolysaccharides can trigger high fever and a life-threatening drop in blood pressure. For this reason, bacterial lipopolysaccharides are referred to as endotoxins.

Gram-negative bacteria have a great facility for exchanging genetic material (DNA) with other strains of the same species and even with different species. Thus, if gram-negative bacteria undergo a genetic change (mutation) that produces resistance to an antibiotic and then share DNA with another strain of bacteria, the second (recipient) strain becomes resistant as well.

Gram-positive bacteria are usually slow to develop resistance to antibiotics. Some gram-positive bacteria (for example, Bacillus anthracis and Clostridium botulinum) produce potent poisons (toxins) that cause serious illness.

A third way of classifying bacteria is by their use of oxygen. Most bacteria can live and grow in the presence of oxygen; these bacteria are called aerobes. Bacteria that can tolerate only low levels of oxygen, or are poisoned by oxygen, are called anaerobes. Anaerobes thrive in areas of the body that have low levels of oxygen—such as the intestine, decaying tissue, and wounds that are particularly deep and dirty.

Hundreds of species of anaerobes normally live harmlessly on the skin and mucous membranes (such as the lining of the mouth, intestine, and vagina); several hundred billion bacteria may exist in a cubic inch of stool. Most anaerobic infections arise from the body's own pool of bacteria.

Anaerobes tend to invade skin and muscle tissue that has been damaged by injury or surgery—particularly if the tissue has a poor blood supply. Spontaneous infections sometimes develop in people who have certain cancers or a weakened immune system. Also common are infections in the mouth. Anaerobes sometimes cause chronic (but not acute) infections of the sinuses and middle ear. Anaerobic infections tend to form collections of pus (abscesses). Severe anaerobic infections often release gas into the surrounding tissue.

Disease-causing anaerobes include clostridia (which live in the intestinal tract of humans and animals, as well as in dust, soil, and decaying vegetation) and Peptococci and Peptostreptococci —which are part of the normal bacterial population (flora) of the mouth, upper respiratory tract, and large intestine. Other anaerobes include Bacteroides, which is part of the normal flora of the large intestine, and Actinomyces, Prevotella, and Fusobacterium, which are part of the normal flora of the mouth.

Notes:

cocci (pl) кокки

bacilli (pl) микробы

spirochetes спирохеты

penetrate проникать

Дата добавления: 2015-11-16