2. 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

Text A Anthrax

Anthrax is a disease caused by the bacterium Bacillus anthracis. which can infect the skin, lungs, and trointestinal tract. Anthrax is a highly contagious and potentially fatal disease. It usually spreads to people from animals, especially cows, goats, and sheep. Dormant bacteria (spores) can live in the soil and in animal products (such as wool) for decades. Although infection in people is usually through the skin, it can also occur from eating contaminated meat or inhaling spores or bacteria.

Symptoms and Diagnosis

Symptoms may appear 12 hours to 5 days after exposure to the bacteria. A skin infection begins as a red-brown bump that enlarges, with considerable swelling at the edges. The bump blisters and hardens, then the center breaks open and oozes a clear fluid before forming a black scab (tschar). Lymph nodes in the affected area may. Knowing that a person has had contact with animals helps a doctor make the diagnosis. To diagnose a pulmonary infection, a doctor may obtain a sputum sample for culture; however, the laboratory isn't always able to identify the bacteria. Sometimes treatment is started when anthrax is suspected but laboratory confirmation isn't available yet.

Prevention and Treatment

People at high risk of contracting anthrax— such as veterinarians, laboratory technicians, and employees of textile mills that process animal hair—can be vaccinated.

An anthrax skin infection is treated with penicillin injections or with oral tetracycline or erythromycin. Lung infections require intravenous penicillin. Other antibiotics also may be given. Corticosteroids may also be used to reduce lung inflammation. If treatment is delayed (usually be cause the diagnosis isn't made promptly), death is likely.

Notes:

anthrax сибирская язва

contaminate инфицировать, заражать

scab (tschar) чесотка