1.
Streptococcus pneumoniae
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Streptococcus pneumoniae, or pneumococcus, is a Gram-positive, alpha-hemolytic or beta-hemolytic, facultative anaerobic member of the genus Streptococcus. As a significant human pathogenic bacterium S. pneumoniae was recognized as a cause of pneumonia in the late 19th century. S. pneumoniae resides asymptomatically in healthy carriers typically colonizing the respiratory tract, sinuses, however, in susceptible individuals with weaker immune systems, such as the elderly and young children, the bacterium may become pathogenic and spread to other locations to cause disease. S. pneumoniae is the cause of community acquired pneumonia and meningitis in children and the elderly. The organism also causes many types of pneumococcal infections other than pneumonia, S. pneumoniae can be differentiated from the viridans streptococci, some of which are also alpha-hemolytic, using an optochin test, as S. pneumoniae is optochin-sensitive. S. pneumoniae can also be distinguished based on its sensitivity to lysis by bile, the encapsulated, Gram-positive coccoid bacteria have a distinctive morphology on Gram stain, lancet-shaped diplococci. The organism was termed Diplococcus pneumoniae from 1920 because of its appearance in Gram-stained sputum. It was renamed Streptococcus pneumoniae in 1974 because it was similar to streptococci. S. pneumoniae played a role in demonstrating that genetic material consists of DNA. In 1944 Oswald Avery, Colin MacLeod, and Maclyn McCarty demonstrated the transforming factor in Griffiths experiment was not protein, as was believed at the time. Averys work marked the birth of the era of genetics. The genome of S. pneumoniae is a closed, circular DNA structure that contains between 2.0 and 2.1 million base pairs depending on the strain. It has a set of 1553 genes, plus 154 genes in its virulome. Genetic information can vary up to 10% between strains, natural bacterial transformation involves the transfer of DNA from one bacterium to another through the surrounding medium. Transformation is a developmental process requiring energy and is dependent on expression of numerous genes. In S. pneumoniae at least 23 genes are required for transformation, in order for a bacterium to bind, take up and recombine exogenous DNA into its chromosome it must enter a special physiological state called competence. Competence in S. pneumoniae is induced by DNA-damaging agents such as mitomycin C, fluoroquinolone antibiotics, transformation protects S. pneumoniae against the bactericidal effect of mitomycin C. On the basis of these findings they suggested that transformation is an adaptation for repairing oxidative DNA damages, S. pneumoniae infection stimulates polymorphonuclear leukocytes to produce an oxidative burst that is potentially lethal to the bacteria
2.
Frederick Griffith
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Frederick Griffith was a British bacteriologist whose focus was the epidemiology and pathology of bacterial pneumonia. He showed that Streptococcus pneumoniae, implicated in cases of lobar pneumonia. The observation was attributed to an unidentified transforming principle or transforming factor and this was later identified as DNA. Americas leading pneumococcal researcher, Oswald T. Avery, speculated that Griffith had failed to apply adequate controls and his discovery was one of the first to show the central role of DNA in heredity. Fred Griffith was born in Hale, Lancashire county, England, in late 1877, thereafter, he worked at the Liverpool Royal Infirmary, the Joseph Tie Laboratory, and the Royal Commission on Tuberculosis. In 1910 Fred Griffith was hired by the government board. Griffith performed the pivotal experiments—actually very many experiments—during the 1920s, with outbreak of World War II, the laboratory was expanded into the Emergency Public Health Laboratory Service. Pneumococci has two general forms—rough and smooth, injected subcutaneously with S form, mice succumbed to pneumonia and death within several days. However, the R form, lacking a capsule—its outer surface being cell wall—is relatively avirulent, when Griffith injected heat-killed S into mice, as expected, no disease ensued. When mice were injected with a mixture of heat-killed S and live R, however, pneumonia, the live R had transformed into S—and replicated as such—often characterized as Griffiths Experiment. Griffith also reported transformation of serological type—bacterial antigenicity—distinct from presence or absence of a capsule, types I, II, and III were each a distinct antigenic grouping, whereas type IV was a catchall of varying antigenicities not matching other types. Averys associate Martin Dawson at The Rockefeller Hospital confirmed each of Griffiths reported findings, even before Griffiths publication, Fred Neufeld had confirmed them as well, and was merely awaiting publication of Griffiths findings before publishing his confirmation. Microbiologists endeavored during the 1930s to dispel the monomorphist tenet, prevailing as institutional dogma, Scott amid an air raid during World War IIs London Blitz. A few weeks earlier, Scott had become director of the laboratory, both dated 3 May 1941, his obituary in The Lancet mentioned the historical discovery briefly, and his obituary in British Medical Journal failed to mention it. In 1944 identification of the factor was published in the Journal of Experimental Medicine by Avery, Colin MacLeod. Biologists made little more than speculation of Griffiths report of transformation until genetics research in 1951, Griffiths report was virtually ignored by clinicians, and by the medical sector as a whole. In 1931 Frederick Griffith coauthored a paper on acute tonsillitis—its sequelae, epidemiology, in 1934, Griffith reported voluminous findings on the serological typing of Streptococcus pyogenes. Streptococcal infection was a frequent coinfection complicating recovery from lobar pneumonia by pneumococci infection
3.
Transformation (genetics)
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Transformation is one of three processes for horizontal gene transfer, in which exogenous genetic material passes from bacterium to another, the other two being conjugation and transduction. In transformation, the material passes through the intervening medium. Transformation in bacteria was first demonstrated in 1928 by British bacteriologist Frederick Griffith, Griffith discovered that a strain of Streptococcus pneumoniae could be made virulent after being exposed to heat-killed virulent strains. Griffith hypothesized that some transforming principle from the strain was responsible for making the harmless strain virulent. In 1944 this transforming principle was identified as being genetic by Oswald Avery, Colin MacLeod and they isolated DNA from a virulent strain of S. pneumoniae and using just this DNA were able to make a harmless strain virulent. They called this uptake and incorporation of DNA by bacteria transformation, the results of Avery et al. It was originally thought that Escherichia coli, a used laboratory organism, was refractory to transformation. However, in 1970, Morton Mandel and Akiko Higa showed that E. coli may be induced to take up DNA from bacteriophage λ without the use of helper phage after treatment with calcium chloride solution. Two years later in 1972, Stanley Norman Cohen, Annie Chang, the method of transformation by Mandel and Higa was later improved upon by Douglas Hanahan. Transformation of animal and plant cells was also investigated with the first transgenic mouse being created by injecting a gene for a rat growth hormone into an embryo in 1982. In 1907 a bacterium that caused plant tumors, Agrobacterium tumefaciens, was discovered, not all plant cells are susceptible to infection by A. tumefaciens, so other methods were developed, including electroporation and micro-injection. Particle bombardment was possible with the invention of the Biolistic Particle Delivery System by John Sanford in the 1980s. In transformation, the material passes through the intervening medium. Competence refers to a state of being able to take up exogenous DNA from the environment. Natural genetic transformation appears to be an adaptation for repair of DNA damage that also generates genetic diversity and it has also been reported in at least 30 species of Proteobacteria distributed in the classes alpha, beta, gamma and epsilon. Naturally competent bacteria carry sets of genes that provide the protein machinery to bring DNA across the cell membrane, the DNA first binds to the surface of the competent cells on a DNA receptor, and passes through the cytoplasmic membrane via DNA translocase. Only single-stranded DNA may pass through, the other strand being degraded by nucleases in the process, the translocated single-stranded DNA may then be integrated into the bacterial chromosomes by a RecA-dependent process. In Gram-negative cells, due to the presence of an extra membrane, pilin may be required for competence, but its role is uncertain
4.
DNA
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Deoxyribonucleic acid is a molecule that carries the genetic instructions used in the growth, development, functioning and reproduction of all known living organisms and many viruses. DNA and RNA are nucleic acids, alongside proteins, lipids and complex carbohydrates, most DNA molecules consist of two biopolymer strands coiled around each other to form a double helix. The two DNA strands are termed polynucleotides since they are composed of simpler units called nucleotides. Each nucleotide is composed of one of four nitrogen-containing nucleobases—cytosine, guanine, adenine, or thymine —a sugar called deoxyribose, and a phosphate group. The nucleotides are joined to one another in a chain by covalent bonds between the sugar of one nucleotide and the phosphate of the next, resulting in an alternating sugar-phosphate backbone. The nitrogenous bases of the two polynucleotide strands are bound together, according to base pairing rules, with hydrogen bonds to make double-stranded DNA. The total amount of related DNA base pairs on Earth is estimated at 5.0 x 1037, in comparison the total mass of the biosphere has been estimated to be as much as 4 trillion tons of carbon. The DNA backbone is resistant to cleavage, and both strands of the double-stranded structure store the same biological information and this information is replicated as and when the two strands separate. A large part of DNA is non-coding, meaning that these sections do not serve as patterns for protein sequences, the two strands of DNA run in opposite directions to each other and are thus antiparallel. Attached to each sugar is one of four types of nucleobases and it is the sequence of these four nucleobases along the backbone that encodes biological information. RNA strands are created using DNA strands as a template in a process called transcription, under the genetic code, these RNA strands are translated to specify the sequence of amino acids within proteins in a process called translation. Within eukaryotic cells DNA is organized into structures called chromosomes. During cell division these chromosomes are duplicated in the process of DNA replication, eukaryotic organisms store most of their DNA inside the cell nucleus and some of their DNA in organelles, such as mitochondria or chloroplasts. In contrast prokaryotes store their DNA only in the cytoplasm, within the eukaryotic chromosomes, chromatin proteins such as histones compact and organize DNA. These compact structures guide the interactions between DNA and other proteins, helping control which parts of the DNA are transcribed, DNA was first isolated by Friedrich Miescher in 1869. DNA is used by researchers as a tool to explore physical laws and theories, such as the ergodic theorem. The unique material properties of DNA have made it an attractive molecule for material scientists and engineers interested in micro-, among notable advances in this field are DNA origami and DNA-based hybrid materials. DNA is a polymer made from repeating units called nucleotides
5.
1918 flu pandemic
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The 1918 flu pandemic was an unusually deadly influenza pandemic, the first of the two pandemics involving H1N1 influenza virus. Disease had already greatly limited life expectancy in the early 20th century, a considerable spike occurred at the time of the pandemic, specifically the year 1918. Life expectancy in the United States alone dropped by about 12 years, most influenza outbreaks disproportionately kill juvenile, elderly, or already weakened patients, in contrast, the 1918 pandemic predominantly killed previously healthy young adults. There are several explanations for the high mortality of the 1918 influenza pandemic. Some research suggests that the variant of the virus had an unusually aggressive nature. Historical and epidemiological data are inadequate to identify the geographic origin. It was implicated in the outbreak of encephalitis lethargica in the 1920s, in Spain, a different nickname was adopted, the Naples Soldier, which came from a musical operetta titled La canción del olvido, which premiered in Madrid during the first epidemic wave. Federico Romero, one of the librettists, quipped that the plays most popular musical number, the site of the very first confirmed outbreak was at Camp Funston, within Fort Riley in Kansas, USA at a military training facility preparing American troops for involvement in World War I. The first victim diagnosed with the new strain of flu on Monday, historian Alfred W. Crosby recorded that the flu originated in Kansas and popular writer John Barry echoed Crosby in describing Haskell County, Kansas, as the point of origin. These researchers postulated that a significant precursor virus, harbored in birds, earlier hypotheses of the epidemics origin have varied. Some hypothesized the flu originated in East Asia and he considered several other hypotheses of origin, such as Spain, Kansas, and Brest, as being possible, but not likely. Political scientist Andrew Price-Smith published data from the Austrian archives suggesting the influenza had earlier origins, in fact, it found evidence that the virus had been circulating in the European armies for months and potentially years before the 1918 pandemic. When an infected person sneezes or coughs, more than half a million virus particles can be spread to those close by, some speculate the soldiers immune systems were weakened by malnourishment, as well as the stresses of combat and chemical attacks, increasing their susceptibility. A large factor in the occurrence of this flu was increased travel. Modern transportation systems made it easier for soldiers, sailors, in the United States, the disease was first observed in Haskell County, Kansas, in January 1918, prompting local doctor Loring Miner to warn the U. S. On 4 March 1918, company cook Albert Gitchell reported sick at Fort Riley, by noon on 11 March 1918, over 100 soldiers were in the hospital. Within days,522 men at the camp had reported sick, by 11 March 1918, the virus had reached Queens, New York. Failure to take measures in March/April was later criticised
6.
Mouse
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A mouse is a small rodent characteristically having a pointed snout, small rounded ears, a body-length scaly tail and a high breeding rate. The best known species is the common house mouse. It is also a popular pet, in some places, certain kinds of field mice are locally common. They are known to invade homes for food and shelter, domestic mice sold as pets often differ substantially in size from the common house mouse. This is attributable both to breeding and to different conditions in the wild, the most well known strain, the white lab mouse, has more uniform traits that are appropriate to its use in research. The American white-footed mouse and the mouse, as well as other common species of mouse-like rodents around the world. These, however, are in other genera, cats, wild dogs, foxes, birds of prey, snakes and even certain kinds of arthropods have been known to prey heavily upon mice. Nevertheless, because of its adaptability to almost any environment. Mice, in contexts, can be considered vermin which are a major source of crop damage, causing structural damage. In North America, breathing dust that has come in contact with mouse excrement has been linked to hantavirus, primarily nocturnal animals, mice compensate for their poor eyesight with a keen sense of hearing, and rely especially on their sense of smell to locate food and avoid predators. Mice build intricate burrows in the wild and these burrows typically have long entrances and are equipped with escape tunnels or routes. In at least one species, the design of a burrow is a genetic trait. Breeding onset is at about 50 days of age in females and males, although females may have their first estrus at 25–40 days. Mice are polyestrous and breed year round, ovulation is spontaneous, the duration of the estrous cycle is 4–5 days and estrus itself lasts about 12 hours, occurring in the evening. Vaginal smears are useful in timed matings to determine the stage of the estrous cycle, mating is usually nocturnal and may be confirmed by the presence of a copulatory plug in the vagina up to 24 hours post-copulation. The presence of sperm on a smear is also a reliable indicator of mating. Female mice housed together tend to go into anestrus and do not cycle, if exposed to a male mouse or the pheromones of a male mouse, most of the females will go into estrus in about 72 hours. This synchronization of the cycle is known as the Whitten effect
. PMID 20474956.
