2

2.6 GENOME PLASTICITY AND EVOLUTION OF ESCHERICHIA COLI
Like all life forms, new strains of E. coli evolve through the natural biological processes of mutation, gene duplication, and horizontal gene transfer; in particular, 18% of the genome of the laboratory strain MG1655 was horizontally acquired since the divergence from Salmonella. E. coli K-12 and E. coli B strains are the most frequently used varieties for laboratory purposes. Some strains develop traits that can be harmful to a host animal. These virulent strains typically cause a bout of diarrhea that is often self-limiting in healthy adults but is frequently lethal to children in the developing world. (Futadar et al., 2005). More virulent strains, such as O157:H7, cause serious illness or death in the elderly, the very young, or the immunocompromised.
The genera Escherichia and Salmonella diverged around 102 million years ago (credibility interval: 57–176 mya), which coincides with the divergence of their hosts: the former being found in mammals and the latter in birds and reptiles. (Wang et al., 2009). This was followed by a split of an Escherichia ancestor into five species (E. albertii, E. coli, E. fergusonii, E. hermannii, and E. vulneris). The last E. coli ancestor split between 20 and 30 million years ago.
The long-term evolution experiments using E. coli, begun by Richard Lenski in 1988, have allowed direct observation of genome evolution over more than 65,000 generations in the laboratory. For instance, E. coli typically do not have the ability to grow aerobically with citrate as a carbon source, which is used as a diagnostic criterion with which to differentiate E. coli from other, closely, related bacteria such as Salmonella. In this experiment, one population of E. coli unexpectedly evolved the ability to aerobically metabolize citrate, a major evolutionary shift with some hallmarks of microbial speciation.
2.7 INCUBATION PERIOD
The time between ingesting the STEC bacteria and feeling sick is called the “incubation period”. The incubation period is usually 3–4 days after the exposure, but may be as short as 1 day or as long as 10 days. The symptoms often begin slowly with mild belly pain or non-bloody diarrhea that worsens over several days. HUS, if it occurs, develops an average of 7 days after the first symptoms, when the diarrhea is improving.

2.7.1 DISCOVERY OF ANTIBIOTICS
• History of antibiotics – 1
19th century:Louis Pasteur & Robert Koch
• History of antibiotics – 2
Plant extracts
– Quinine (against malaria)
– Ipecacuanha root (emetic, e.g. in dysentery)
Toxic metals
– Mercury (against syphilis)
– Arsenic (Atoxyl, against Trypanosoma)
• Dyes
– Trypan Blue (Ehrlich)
– Prontosil (azo-dye, Domagk, 1936)
• History of antibiotics – 3
Paul Ehrlich
• started science of chemotherapy
• Systematic chemical modifications
(“Magic Bullet”) no. 606 compound = Salvarsan (1910)
• Selective toxicity.
• Developed the Chemotherapeutic Index
• History of antibiotics – 4
Penicillin- the first antibiotic – 1928• Alexander Fleming observed the
killing of staphylococci by a fungus (Penicillium notatum)
• observed by others – never exploited
• Florey & Chain purified it by freeze-drying (1940) – Nobel prize 1945
• First used in a patient: 1942
• World War II: penicillin saved 12-15% of lives
• History of antibiotics – 5
Selman Waksman – Streptomycin (1943), was the first scientist who discovered antibiotic active against all Gram-negatives for examples; Mycobacterium tuberculosis
– Most severe infections were caused by Gram-negatives and Mycobacterium
tuberculosis, extracted from Streptomyces – extracted from Streptomyces
– 20 other antibiotics include. neomycin, actinomycin
2.8 CHARACTERISTICS OF ANTIBIOTICS
According to the Oxford Dictionary, the term Antibiotics encompasses medicines (such as penicillin or its derivatives) that inhibit the growth of or destroys microorganisms. Antibiotics are naturally occurring substances that exhibit inhibitory properties towards microbial growth at high concentrations. (Zaffiri, et al., 2012).
-Antibiotics are selective in their effect on different microorganisms, being specific in their action not only against genera and species but even against strains and individual cells. Some of these agents act mainly on gram-positive bacteria, while others inhibit only gram-negative ones.
-Some antibiotics are produced by some organism, from different strains of penicillin.
-Bacteria are sensitive to the antibiotic which enable them to developed resistance after contact, for several periods.

2.9 ROLE OF ANTIBIOTICS
Based on the clinical use of antibiotics, it may appear that these compounds play a similar role as microbial weapons in nature, yet this seems unlikely due to the fact that the concentrations used in the clinical setting are significantly higher than that produced in nature (Fajardo et al., 2008). Due to experimental evidence, it makes more sense to see antibiotics as small, secreted molecules involved in cell-to-cell communication within microbial communities.
(Martinez, 2008). Diverse Studies have been conducted in which different antibiotics and antibiotic-like structures were administered to different bacterial species at levels below the compounds minimum inhibitory concentrations (MIC). (Fajardo et al., 2008). that was

Best services for writing your paper according to Trustpilot

Premium Partner
From $18.00 per page
4,8 / 5
4,80
Writers Experience
4,80
Delivery
4,90
Support
4,70
Price
Recommended Service
From $13.90 per page
4,6 / 5
4,70
Writers Experience
4,70
Delivery
4,60
Support
4,60
Price
From $20.00 per page
4,5 / 5
4,80
Writers Experience
4,50
Delivery
4,40
Support
4,10
Price
* All Partners were chosen among 50+ writing services by our Customer Satisfaction Team

2

2). The conditions of hukm (legal ruling)
Hukm is a ruling of the original case that has been mentioned in the Quran and Sunnah in which it also includes the ruling made through ijma’. Hukm is important in qiyas as it will be an extension to the a new case in applying analogical deduction. There are some conditions that a hukm must be fulfilled in order to make a qiyas valid which are practical, operative, rational, not confined and not an exceptional hukm in which these will be discussed further.
The first condition is a hukm must be practical in nature. A qiyas can only be made when the hukm is related to practical matters. Besides, a hukm must also be found in the three sources, the Quran, Sunnah and ijma’ as the extended rulings cannot form the basis of qiyas. In other words, it must be hukm al-asl.
Next, a hukm must be an operative ruling in which the hukm is a non- abrogated hukm. An abrogated hukm cannot be used as an extension to the new case as well as a hukm that has controversy and disagreement on its validity. Besides, a hukm also must be rational in which the ‘illah, effective cause of it can be understood by human intellect or the ‘illah has already been mentioned in the text. For example, the ‘illah for prohibition of wine clearly has been mentioned in the Quran, which is intoxication of mind while the ‘illah behind the prohibition of gambling can easily be perceived. In contrast, hukm in regards to matters such as the number of prostration in salah or the quantity of zakah cannot be used in analogical deduction. Matters on ibadah are not suitable to be used in deducing qiyas on the new case as Allah is the one who only knows the wisdom behind them. According to Imam Abu Hanifah, the causes behind the clear textual rulings of Shariah can be determined except the one that falls under ibadah whereas the Zahiris and Uthman al-Batti have different opinion in which the causes behind the clear textual rulings cannot be determined unless they have been mentioned in text.
Furthermore, a hukm should also not be confined to a particular matter. For examples, the rulings on Prophet Muhammad regarding the marriage more than four wives and the prohibition of marrying the wives of Prophet after his demise, cannot be extended to others as Allah has made these specifically for Prophet Muhammad. In addition, issues on polygamy and marriage of a widow have clearly mentioned by Allah in the Quran in which Allah has permitted a man to have a maximum number of four wives and a widow to remarry after completing her iddah.
Lastly, a hukm that is exceptional cannot be extended to the new case. This means an exceptional hukm refers to a ruling that has been made due to some exceptional conditions from its original ruling. As an example, breaking fast during Ramadan is not permissible unless the person faces some situation or condition that allow him to discontinue his fasting such as travelers, a sick person and a labor man. However, according to the Shafi ‘is, the exceptional hukm can be used in extending to the new case as long as the effective cause is identified. As an example, in a transaction, a fresh dates on a tree is exceptionally permissible to be exchanged with dry dates as mentioned in a Hadith though this contains an usury element in which the act of exchanging things that are identical but unequal in quantity. The reason behind this permissibility is because of the ‘illah in which the need of the owner has been fulfilled. Due to this, this exceptional ruling is extended to the case of exchanging grapes with raisins which the hukm is acceptable and valid according to the Shafi ‘is as long as the needs of the owners are being fulfilled. On the other hand, the Hanafis have disagreed on this ruling because it is an exceptional case.