examples of Bacteria


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The Clostridia are a highly polyphyletic class of Bacillota, including Clostridium and other similar genera. They are distinguished from the Bacilli by lacking aerobic respiration. They are obligate anaerobes and oxygen is toxic to them. Species of the class Clostridia are often but not always Gram-positive (see Halanaerobium) and have the ability to form spores.Studies show they are not a monophyletic group, and their relationships are not entirely certain. Currently, most are placed in a single order called Clostridiales, but this is not a natural group and is likely to be redefined in the future.

Most species of the genus Clostridium are saprophytic organisms that ferment plant polysaccharides  and are found in many places in the environment, most notably the soil. However, the genus does contain some human pathogens . The toxins produced by certain members of the genus Clostridium are among the most dangerous known. Examples are tetanus toxin (known as tetanospasmin) produced by C. tetani and botulinum toxin produced by C. botulinum. Some species have been isolated from women with bacterial vaginosis.

Notable species of this class include:

Heliobacteria and Christensenella are also members of the class Clostridia.

Some of the enzymes produced by this group are used in bioremediation.


Listeria monocytogenes is the species of pathogenic bacteria that causes the infection listeriosis. It is a facultative anaerobicbacterium, capable of surviving in the presence or absence of oxygen. It can grow and reproduce inside the host's cells and is one of the most virulent foodborne pathogens: 20 to 30% of foodborne listeriosis infections in high-risk individuals may be fatal.Responsible for an estimated 1,600 illnesses and 260 deaths in the United States annually, listeriosis ranks third in total number of deaths among foodborne bacterial pathogens, with fatality rates exceeding even Salmonella spp.and Clostridium botulinum. In the European Union, listeriosis follows an upward trend that began in 2008, causing 2,161 confirmed cases and 210 reported deaths in 2014, 16% more than in 2013. Listeriosis mortality rates are also higher in the EU than for other foodborne pathogens

Listeria monocytogenes is a Gram-positivebacterium, in the phylum Bacillota, named after Joseph Lister. Its ability to grow at temperatures as low as 0 °C permits multiplication at typical refrigeration temperatures, greatly increasing its ability to evade control in human foodstuffs. Motile via flagella at 30 °C and below, but usually not at 37 °C,[6] L. monocytogenes can instead move within eukaryotic cells by explosive polymerization of actin filaments (known as comet tails or actin rockets).

Studies suggest up to 10% of human gastrointestinal tracts may be colonized by L. monocytogenes. Nevertheless, clinical diseases due to L. monocytogenes are more frequently recognized by veterinarians, especially as meningoencephalitis in ruminants. See: listeriosis in animals.

Due to its frequent pathogenicity, causing meningitis in newborns (acquired transvaginally), pregnant mothers are often advised not to eat soft cheeses such as BrieCamembertfeta, and queso blanco fresco, which may be contaminated with and permit growth of L. monocytogenes. It is the third-most common cause of meningitis in newborns. Listeria monocytogenes can infect the brain, spinal-cord membranes and/or the bloodstream of the host. through the ingestion of contaminated food such as unpasteurized dairy or raw foods

Corynebacterium diphtheriaeis the pathogenic bacterium that causes diphtheria.It is also known as the Klebs–Löffler bacillus.

Four subspecies are recognized: C. d. mitis, C. d. intermedius, C. d. gravis, and C. d. belfanti. The four subspecies differ slightly in their colonial morphology and biochemical properties, such as the ability to metabolize certain nutrients, but all may be toxigenic (and therefore cause diphtheria) or not toxigenic.  C. diphtheriae produces diphtheria toxin which alters protein function in the host by inactivating the elongation factor EF-2. This causes pharyngitis and 'pseudomembrane' in the throat. The diphtheria toxin gene is encoded by a bacteriophage found in toxigenic strains, integrated into the bacterial chromosome.

To accurately identify C. diphtheriae, a Gram stain is performed to show Gram-positive, highly pleomorphic organisms with no particular arrangement. Special stains like Albert's stain and Ponder's stain are used to demonstrate the metachromatic granulesformed in the polar regions. The granules are called polar granules, Babes Ernst granules, volutin granules etc. An enrichment medium, such as Löffler's medium, is used to preferentially grow C. diphtheriae. After that, a differential plate known as tellurite agar, allows all Corynebacteria (including C. diphtheriae) to reduce tellurite to metallic tellurium. The tellurite reduction is colorimetrically indicated by brown colonies for most Cornyebacteriumspecies or by a black halo around the C. diphtheriae colonies.

A low concentration of iron is required in the medium for toxin production. At high iron concentrations, iron molecules bind to an aporepressor on the beta bacteriophage, which carries the Tox gene. When bound to iron, the aporepressor shuts down toxin production.Elek's test for toxigenicity is used to determine whether the organism is able to produce the diphtheria toxin.


Corynebacterium diphtheriae is the bacterium that causes the disease diphtheria.  C. diphtheriae is a rod-shaped, Gram-positive, nonspore-forming, and nonmotile bacterium.The disease occurs primarily in tropical regions and underdeveloped countries, but has been known to appear throughout the world. Immunocompromised individuals, poorly immunized adults, and unvaccinated children are at the greatest risk for contracting diphtheria. During the typical course of disease, the only affected body region is the upper respiratory system. A thick, gray coating accumulates in the nasopharyngeal region, making breathing and swallowing more difficult. The disease remains contagious for at least two weeks following disappearance of symptoms, but has been known to last for up to a month. The most common routes of entry for C. diphtheriae are the nose, tonsils, and throat. Individuals suffering from the disease may experience sore throat, weakness, fever, and swollen glands.

Staphylococcus aureus 

is a gram-positive, catalase-positive, coagulase-positive cocci in clusters. S. aureus can cause inflammatory diseases, including skin infections, pneumonia, endocarditis, septic arthritis, osteomyelitis, and abscesses. S. aureus can also cause toxic shock syndrome (TSST-1), scalded skin syndrome (exfoliative toxin, and food poisoning (enterotoxin). 

Staphylococcus epidermis (scientific name: Staphylococcus epidermidis)

is a type of bacteria belonging to the genus Staphylococcus of the family Staphylococcus .Staphylococcus epidermidis is a type of Gram-positive bacteria and one of more than 40 species belonging to the genus Staphylococcus. It is part of the normal human microflora, usually the cutaneous microflora, and less commonly the mucosal microflora. Although S. epidermidis does not usually cause disease, patients with compromised immune systems are at risk of infection. This infection is usually acquired from hospitals.Staphylococcus epidermidis is of particular concern to people undergoing catheters or other surgical implants because it is known to form the biofilms that grow on these devices.Being part of the normal cutaneous microflora, S. epidermidis is a frequent contaminant of samples sent to the laboratory fromdiagnosis[].


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