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الطب | الأمراض | العلوم | الأحياء | الصحة 8‏/3‏/2011 تم النشر بواسطة one way.
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اشيرشيا كولي ..........هذه هي البكتيريا التي اعرفها
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هذه البكتريات  تعيش في التراب والمياه  والنباتات   مع  صور  مفصلة
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What is bacteria?

Bacteria is a single-celled organism which can only be seen through microscope. Bacteria comes in different shapes and the size of bacteria is measured in micro-meter (which is a millionth part of a meter). Bacteria are found everywhere and in all type of environments.

There are numerous types of bacterial in the world. Before the invention of DNA sequencing technique, bacteria were mainly classified based on their shapes, which is also known as Morphology, biochemistry and staining (which is either Gram Positive or Gram Negative). Now a day along with the morphology, DNA sequencing is also used in order to classify bacteria. (DNA sequencing also helps in understanding relationship between two types of bacteria if they are related to each other despite of their shapes). Along with the shape and DNA sequence, other things such as their metabolic activities, conditions required for their growth, biochemical reactions (i.e. biochemistry as mentioned above), antigenic properties, and other characteristics are also helpful in classifying the bacteria.

There are various groups of bacteria, which belong to same family and are evolved from same bacteria (ancestor). However, each types of bacteria posses its own characteristics (those which are evolved after separation from the original specie).



http://www.typesofbacteria.co.uk/images/27388.jpg

The Two Main Groups
Taking a big overview of bacteria, there are two main groups, the bacteria and the cyanobacteria. Bacteria include all of the commonly known species such as Escherichia coli (E. coli bacteria), Salmonella bacteria, Staphylococci, Listeria and the Clostridia. Cyanobacteria form a separate type of bacteria that are able to photosynthesise – they can also be called blue-green algae.

Cyanobacteria still exist in large numbers today but their importance in the development of life on Earth is due to their existence here millions of years ago. Cyanobacteria were very successful and grew everywhere. Their ability to photosynthesise created all the oxygen that is in our atmosphere today. Most living organisms today depend on oxygen and without cyanobacteria, it is very unlikely that this life would have evolved.


Types of Bacteria
There are seven main groups of bacteria, distinguished by their shape and the type of cell wall they possess. Four of the seven types make up the majority of all bacteria:


Gram positive cocci
Gram negative cocci
Gram positive bacilli
Gram negative bacilli

Cocci are spherical cells, bacilli are rod-shaped. Bacteria of either shape that have thick cell walls are termed gram positive because of the way they take up the Gram stain. Those with thin cell walls are termed gram negative. These four main types are described in more detail below.

There are also three other, more rare types of bacteria:

Spirochaetes: corkscrew-shaped bacteria that fall into three species, all of which cause specific diseases. Treponema bacteria cause syphilis and yaws, Leptospira bacteria cause leptospirosis and Borrelia bacteria cause Lyme disease.
Rickettsia: bacteria from the Rickettsiaceae family, which can only live and survive inside other living cells. One type causes the disease typhus.
Mycoplasma: bacteria that have no cell wall. These can infect humans and cause pneumonia
8‏/3‏/2011 تم النشر بواسطة mezo221144 (مازن بدرية).
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1-بكتريا السالمونيلا          Salmonella              تسبب أمراض حمى التيفوئيد والنزلات المعوية.
2-بكتريا الشيجالا             Shigalla                    تسبب أمراض الإسهال.
3-بكتريا الأسثريشيا كولاي  Escherichia coli        أمراض الجفاف Dehydration والإسهال والقيء عند الأطفال بصفة خاصة.
4-بكتريا اللبتوسبيرا          Leptospira               ينجم عنها حدوث التهابات الكلى والكبد والجهاز العصبي المركزي .
5-بكتريا الفيبريو              Vibrio                   تسبب مرض الكوليرا
8‏/3‏/2011 تم النشر بواسطة Texas.
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راجع كتاب البكتيريا في المياه والتربه
8‏/3‏/2011 تم النشر بواسطة محمد قيس (Mohammed Qais).
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water borne bacterial
Causative organisms
1- Cholera
Epidemiology : Spread by the bacterium Vibrio cholerae Drinking water contaminated with the bacterium.
Clinical presentation :
In severe forms it is known to be one of the most rapidly fatal illnesses known. Symptoms include very watery diarrhoea, nausea, cramps, nosebleed, rapid pulse, vomiting, and hypovolemic shock (in severe cases), at which point death can occur in 12–18 hours.
Diagnosis:
In epidemic situations, a clinical diagnosis is made by taking a history of symptoms from the patient and by a brief examination only. Treatment is usually started without or before confirmation by laboratory analysis of specimens.Stool and swab samples collected in the acute stage of the disease, before antibiotics have been administered, are the most useful specimens for laboratory diagnosis. If an epidemic of cholera is suspected, the most common causative agent is Vibrio cholerae O1. If V. cholerae serogroup O1 is not isolated, the laboratory should test for V. cholerae O139. However, if neither of these organisms is isolated, it is necessary to send stool specimens to a reference laboratory. Infection with V. cholerae O139 should be reported and handled in the same manner as that caused by V. cholerae O1. The associated diarrheal illness should be referred to as cholera and must be reported.A number of special media have been employed for the cultivation for cholera vibrios.

Causative organisms
2-Shigella Dysentery.
Epidemiology :
Water contaminated with the bacterium .
Clinical presentation :
Frequent passage of feces with blood and/or mucus and in some cases vomiting of blood.
Diagnosis:
Shigella is a genus of Gram-negative, non-spore forming rod-shaped bacteria closely related to Escherichia coli and Salmonella

Causative organisms
3- Leptospira.
Epidemiology :
Water contaminated by the animal urine carrying the bacteria
Clinical presentation :
Begins with flu-like symptoms then resolves. The second phase then occurs involving meningitis, liver damage (causes jaundice), and renal failure
Diagnosis:
On infection the microorganism can be found in blood for the first 7 to 10 days (invoking serologically identifiable reactions) and then moving to the kidneys. After 7 to 10 days the microorganism can be found in fresh urine. Hence, early diagnostic efforts include testing a serum or blood sample serologically with a panel of different strains. It is also possible to culture the microorganism from blood, serum, fresh urine and possibly fresh kidney biopsy. Kidney function tests (Blood Urea Nitrogen and creatinine) as well as blood tests for liver functions are performed. The latter reveal a moderate elevation of transaminases. Brief elevations of aspartate aminotransferase (AST), alanine aminotransferase (ALT), and gamma-glutamyltransferase (GGT) levels are relatively mild. These levels may be normal, even in children with jaundice. Diagnosis of leptospirosis is confirmed with tests such as Enzyme-Linked Immunosorbent Assay (ELISA) and PCR. Serological testing, the MAT (microscopic agglutination test), is considered the gold standard in diagnosing leptospirosis. As a large panel of different leptospira need to be subcultured frequently, which is both laborious and expensive, it is underused, mainly in developing countries.
Differential diagnosis list for leptospirosis is very large due to diverse symptomatics. For forms with middle to high severity, the list includes dengue fever and other hemorrhagic fevers, hepatitis of various etiologies, viral meningitis, malaria and typhoid fever. Light forms should be distinguished from influenza and other related viral diseases. Specific tests are a must for proper diagnosis of leptospirosis. Under circumstances of limited access (e.g., developing countries)

( Soilborne Bacterial Diseases)
Causative organisms
1-Anthrax       Cause: Bacillus anthracis
Epidemiology :
Individuals at risk for anthrax include those in contact with infected animals or animal products. Episodes of B cereus food poisoning occur sporadically worldwide and result from ingestion of contaminated food in which the bacteria have multiplied to high levels under conditions of improper storage after cooking.
Contact with contaminated soil
Livestock
Through skin; wounds; abrasions
Also through oral route or airborne
Clinical presentation :
Main article: Anthrax
Three forms of anthrax disease are recognized based on their form of inoculation.

Cutaneous
the most common form (95%), causes a localized inflammatory black necrotic lesion (eschar)
Pulmonary
highly fatal and characterized by sudden massive chest edema followed by cardiovascular shock
Gastrointestinal
rare but also fatal (causes death to 25%) type results from ingestion of spores
Diagnosis:
Cutaneous anthrax is diagnosed on the basis of the characteristic papule (early) or eschar (later) with extensive surrounding edema, backed by a history of exposure to animals or their products. Diagnosis is confirmed by observation of characteristic encapsulated bacilli in polychrome methylene blue-stained smears of blood, exudate, lymph, cerebrospinal fluid, etc., and/or by culture. Other Bacillus infections are diagnosed by culture of the bacteria.
Methylene Blue staining of Bacillus anthracis showing the spores as dark blue with the vegetative cells staining red.
Gram stain of Bacillus anthracis showing Gram-positive rods forming long filaments.
Visualization of the capsule of Bacillus anthracis using an Indian ink stain.
Colonial growth of Bacillus anthracis. When lifted by an inoculation loop, colonies, in this case on sheep blood agar, show a tenacity that allows them to be pulled up and stay upright with a texture similar to egg whites beaten to a stiff peak.
Encapsulation test for Bacillus anthracis. The difference in appearance of colonies on bicarbonate agar (smooth colonies on the left) and rough colonies (sheep blood agar on the right) is indicative of capsule formation.
Rods of Bacillus anthracis in lung tissue (B&B stain)

2-Tetanus   Cause: Clostridium tetani
Epidemiology :
Clinical presentation :
Tetanospasmin is distributed in the blood and lymphatic system of the host. The toxin acts at several sites within the central nervous system, including peripheral nerve terminals, the spinal cord, and brain, and within the sympathetic nervous system. The toxin is taken up into within the nerve axon and transported across synaptic junctions, until it reaches the central nervous system, where it is rapidly fixed to gangliosides at the presynaptic junctions of inhibitory motor nerve endings
Diagnosis:
Wound exudate is examined microscopically for the presence of gram positive bacilli with drum-stick appearance .
The exudate is cultured on blood agar incubated anaerobically ,and on robertson cooked meat medium .

Causative organisms
3-Gas Gangrene Often caused by Clostridium perfringins
Epidemiology : It is a saprophyte, meaning it occurs in soil, H2O, decomposing plant, human and animal feces .
Clinical presentation :
Clostridium perfringens is commonly encountered in infections as a benign component of the normal flora.Infections due to C. perfringens show evidence of tissue necrosis, bacteremia, emphysematous cholecystitis, and gas gangrene, which is also known as clostridial myonecrosis. The toxin involved in gas gangrene is known as α-toxin, which inserts into the plasma membrane of cells, producing gaps in the membrane that disrupt normal cellular function.After ingestion, bacteria multiply and lead to colic, diarrhea, and sometimes nausea.The action of C. perfringens on dead bodies is known to mortuary workers as tissue gas and can be halted only by embalming.
Diagnosis:
On blood agar plates, C. perfringens grown anaerobically produces β-haemolytic, flat, spreading, rough, translucent colonies with irregular margins. A Nagler agar plate, containing 5-10% egg yolk, is used to identify strains that produce α-toxin, a diffusible lecithinase that interacts with the lipids in egg yolk to produce a characteristic precipitate around the colonies. One-half of the plate is inoculated with antitoxin to act as a control in the identification .
8‏/3‏/2011 تم النشر بواسطة ÂĐèĿ.
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