Exercise 27. Match symptoms with the disease.
| Scrapie | an abnormal gait, changes in behavior, tremors and hyper-responsiveness; hindlimb ataxia; aggression, anxiety relating to certain situations, nervousness, frenzy and an overall change in temperament; persistent pacing, rubbing or licking; weight loss, decreased milk production, lameness, ear infections and teeth grinding due to pain |
| BSE | weight loss over time; decreased interactions with other animals,listlessness, lowering of the head, tremors, repetitive walking in set patterns, and nervousness; excessive salivation and grinding of the teeth are observed; increased drinking and urination |
| CWD | tremor (especially of head and neck), pruritus, and locomotor incoordination; scratching and rubbing against fixed objects, scraping their fleeces, loss of coordination, weight loss despite retention of appetite, biting of feet and limbs, lip smacking, gait abnormalities, high-stepping of the forelegs, hopping like a rabbit, and swaying of the back end |
UNIT 4
BACTERIA AND BACTERIA RELATED DISEASES
TEXT A
BACTERIA CLASSIFICATION
VOCABULARY LIST TO TEXT A
| archaen pl | [ɑːˈkɪə] | археи |
| bacillus (bacilli)n | [bəˈsɪl.əs][-aɪ] | бацилла |
| beneficial adj | [ˌben.ɪˈfɪʃ.əl] | полезный |
| coccus (cocci) n | [ˈkɒkəs][ -aɪ] | кокк |
| cytoplasm n | [ˈsaɪ.tə.plæz.əm ] | цитоплазма |
| eukaryote n | [yuːˈkærɪəʊt] | эукариот |
| gangrene n | [ˈɡæŋ.ɡriːn] | гангрена |
| harmless adj | [ˈhɑːmləs] | безвредный |
| nitrogen n | [ˈnaɪ.trə.dʒən ] | азот |
| nucleus (nuclei) n | [ˈnjuː.kli.əs] | ядро |
| obligate adj | [ˈɒblɪgeɪt] | облигатный |
| peptidoglycan n | [ˈpeptɪdəˈglaɪˌkən] | пептидогликан |
| prokaryoten | [ˈprəʊˈkærɪəʊt] | прокариот |
| property n | [ˈprɒpəti] | качество, свойство |
| tetanus n | [ˈtetənəs ] | столбняк |
| scheme n | [skiːm] | система, план |
| withstand v | [wɪðˈstænd] | выдерживать |
Bacteria were the first organisms to appear on earth, about 4 billion years ago. They are tiny single-cell microorganisms, usually a few micrometers in length that normally exist together in millions. Bacteria can be found virtually everywhere. Scientists who specialize in bacteria – bacteriologists – say bacteria are found absolutely everywhere except for places that have been sterilized. Even the most unlikely places with extreme temperatures or high concentration of toxic chemicals, have bacteria. A gram of soil typically contains about 40 million bacterial cells. A milliliter of fresh water usually holds about one million bacterial cells. A bacterial cell differs from the cell of a plant or animal. Bacterial cells have no nucleus. An organism without a nucleus is called a prokaryote. Bacteria and archaea are the only prokaryotes. All other life forms are eukaryotes, creatures whose cells have nuclei.There are three basic bacterial shapes. Round bacteria are referred to as cocci (singular: coccus); cylindrical or rod shaped bacteria are known as bacilli (singular: bacillus); and spiral bacteria are called spirilla (singular: spirillum). Cocci can associate with one anotherin different configurations: combinations of two or diplococcus; a linear chain or streptococcus; and a cluster or staphylococcus. The shapes and configurations of bacteria are often reflected in their names. For example, the milk-curdling Lactobacillus acidophilus arebacilli, and pneumonia-causing Streptococcus pneumonia are a chain of cocci.
Most people tend to imagine negative things when asked about bacteria. However, it is important to remember that bacteria can be beneficial, too. Lactic acid bacteria, such as Lactobacillus and Lactococcus together with yeast and fungi have been used for the preparation of such foods as cheese, soy sauce, vinegar, yoghurt and pickles. Humans have been using these bacteria for preparing fermented foods for thousands of years. The human and animal body contains huge amounts offriendly bacteria that are either neutral, harmless or helpful. Bacteria in the digestive system are crucial for the breakdown of certain types of nutrients, such as complex sugars, into forms the body can use. However, several species of bacteria are pathogenic, that is they can cause infectiousdiseases, including cholera, tuberculosis and others. For example, bacillus anthracis causes anthrax, a deadly disease in cattle and a potential bioweapon against humans.
The identification of bacteria in the laboratory is particularly important inmedicine, where the correct treatment depends on the identification of bacterial species causing an infection. There are many classifications of bacteria. The most important feature for all classification systems is that an organism, identified by one individual (scientist, clinician or epidemiologist), is recognized as the same organism by another individual. At present the typing schemes٭ used by clinicians, clinical microbiologists rely on phenotypic typing schemes٭. These schemes use the bacterial morphology (structure) and staining properties of the organism as well as O2 growth requirements of the species combined with a variety of biochemical tests and, if needed, serological tests.
Gram stain. Of all classification systems, the Gram stain has withstood the test of time. Developed in 1884 by Hans Christian Gram, it allows a large proportion of clinically important bacteria to be classified as either Gram positive or negative based on their morphology and differential staining properties. The thick layers of peptidoglycan in the "gram-positive" cell wall stain purple, while the thin "gram-negative" cell wall appears pink. By combining morphology and Gram-staining, most bacteria can be classified as belonging to one of four groups (gram-positive cocci, gram-positive bacilli, gram-negative cocci and gram-negative bacilli). Gram-positive and gram-negative bacteria cause different types of infections, and different types of antibiotics are effective against them. Some Gram-positive bacteria are also capable of forming spores under stressful environmental conditions such as when there is limited availability of carbon and nitrogen. The spore has a hard protective coating that encases the key parts of the bacterium –peptidoglycan,cytoplasm, water, and bacterial DNA. These factors make it nearly impossible to eliminate bacterial spores, and they are found in many places, especially in food products. Thus, spores are structures produced by bacteria, which help them to survive in unfavorable environment including extreme temperatures, lack of moisture, drought, different chemicals and radiation. They do not have any role in reproduction. When conditions become more favorable again – when there’s more water or more food available – the bacterium "comes to life" again, transforming from a spore back to a cell.
Growth requirements. Bacteria can also be grouped by whether they need oxygen to live and grow. Those that need oxygen are called aerobes. Those that do not use oxygen are called anaerobes. Obligate aerobes cannot live without oxygen. Obligate anaerobes cannot live in the presence of oxygen. Facultative anaerobes are those, which can grow without oxygen but use oxygen if it is present. Aerobic bacteria may cause serious problems to people's infrastructure as they can cause corrosion, problems with water clarity, and bad smells. Anaerobic bacteria are most commonly found in the gastrointestinal tract. They can cause gas gangrene and tetanus. Most dental infections are also caused by this type of bacteria. Facultative anaerobes are most commonly found in soil, water, vegetation. An example of a facultative anaerobic bacterium is salmonella.
Bacterial species are identified in microbiology laboratories. Medical microbiologists often serve as consultants to doctors providing identification of bacteria and suggesting ways of treatment.
٭typing schemes – схемытипирования
٭phenotypic typing scheme – схемафенотипическоготипирования
EXERCISES TO THE TEXT