#4 Bacteria

Natural Products-Module 4

Core Concepts

Antimicrobials: a substance that kills or inhibits the growth of microorganisms (including: fungi, protozoans, and fungi).

Microbiocidal: a substance kills the microorganism
Microbiostatic: Prevents microorganism from growing
Antibiotic resistance: drug resistance where a microorganism is able to survive exposure to an antibiotic
Horizontal gene transfer: the process in which an organism incorporates genetic material from another organism that is not their parent. In microorganisms this is the common mechanism in which new species acquire antibiotic resistance. gene transfer (http://www.youtube.com/watch?v=t4i0Q_irM8o)
Bacteria characteristics: single-celled, small (generally only as big as a few micrometers), lacks true nucleus, wide range of growth shapes (see image below), wide range of habitats. Classification of bacteria was traditional based on growth requirements, shape, and cell wall structures. However, now reclassification is occurring and is based on genetic data (see image below from http://tolweb.org).

 

Bacteria diversity (http://www.youtube.com/watch?v=N-EYTtxsL8g&feature=fvwrel)

 

History

(from Discovery, Chance and the Scientific Method By: Fran Slowiczek, and Pamela M. Peters http://www.accessexcellence.org/AE/AEC/CC/chance.php)

In the late 1800's bacteriologists and microbiologists set out to identify substances with therapeutic potential. One of the greatest problems faced by these scientists during their studies was the contamination of "pure" cultures by invading microorganisms especially fungi or bacteria - a problem which still plagues the modern day microbiologist (and you will have problems with this also). It is this problem of contamination which is most often identified as leading to the "chance" observation that eventually led to the discovery of penicillin.

These studies of contaminated cultures led to a series of observations by late 19th century bacteriologists and microbiologists describing the effect of mold on bacterial growth. These observations were as follows:

• In 1874, William Roberts (1830-99) observed that cultures of the mold Penicillin glaucum did not exhibit bacterial contamination.
• French scientists Louis Pasteur (1822-95) and Jules Francois Joubert (1834-1910) observed that growth of the anthrax bacilli was inhibited when the cultures became contaminated with mold.
• The English surgeon Joseph Lister (1827-12) noted in 1871 that samples of urine contaminated with mold did not allow the growth of bacteria. Lister unsuccessfully attempted to identify the agent in the mold which inhibited bacterial growth. He later abandoned this research for the more successful work of introducing antiseptic procedures and sterile instruments into the operating theater.

Another event, although overlooked at the time, in the string of occurrences which led to the discovery of penicillin was a dissertation written in 1897 by the French medical student, Ernest Duchesne. In his dissertation, Duchesne reported the discovery, partial refinement, and successful testing on animals of a substance with antibiotic properties - that is a substance which inhibited bacterial growth. The source of Duchesne's substance was the mold penicillin.
Thus the stage was set for the "chance" discovery of penicillin by Alexander Fleming in 1928. In most science textbooks, from middle school to college level, Fleming, alone, is credited with the discovery of penicillin. Yet, Fleming's discovery would have been nothing more than a fluke had the base of knowledge provided, at least in part, by the chance observations of Roberts, Pasteur, Lister, Joubert and others, not existed. Without a doubt, Fleming was searching for antibacterial agents. As early as 1922, he had discovered an enzyme present in biological substances as varied as egg whites, tears and mucus that causes bacteria to lyse, or burst. However, he was unable to successfully isolate the active ingredient in these materials.
In 1928, he was researching the properties of the group of bacteria known as staphylococci and became another in the long line of scientists to benefit from a seemingly chance observation. His problem during this research was the frequent contamination of culture plates with airborne molds. One day he observed a contaminated culture plate and noted that the Staphylococci bacteria had burst in the area immediately surrounding an invading mold growth. He realized that something in the mold was inhibiting growth of the surrounding bacteria. Subsequently Fleming isolated an extract from the mold and he named it penicillin. Despite this success, further attempts by Fleming to produce a concentrated extract of penicillin failed and he was unable to prove its therapeutic value.
It wasn't until ten years later, in 1939, that Ernst Chain, Howard Florey and Edward Abraham of Oxford University were able to purify and stabilize a form of penicillin that enabled demonstration of its therapeutic potential. Again, chance favored their work. Unknown to them, the species of animal that they chose for laboratory studies turned out to be one of few species that do not find penicillin toxic. Had they chosen to work with a species other than the one they chose, they might have deemed penicillin too toxic for use, and humankind would have been deprived of the phenomenal life-saving ability of this drug.
The first human trial of penicillin took place in 1941 and involved treating a man with osteomyelitis. Although the treatment produced improvement, the patient, a policeman, died when the limited supply of penicillin was exhausted. (Penicillin was so scarce that the patient's urine was collected and the excreted penicillin was recrystallized to be used again.) Despite the sad ending to this initial penicillin treatment, the therapeutic efficacy of penicillin was accepted. Interest in penicillin soared with the onset of World War II and bombings in England. These events gave great urgency to development of a process which would produce medicinal penicillin in sufficient quantities to treat ever increasing numbers of war wounds. But the British pharmaceutical industry was unable to cope with increasing wartime demands, not only for penicillin but for more traditional medicines, as well.
In an act of daring, Ernst Chain sailed across the sub-infected Atlantic to the United States to find the needed technology for mass production of the new drug. Chain turned to a beer-brewing technology to produce the huge amounts of the moldy liquor which was needed for penicillin production. The moldy liquor underwent a slow purification process to produce the large amounts of clinically usable penicillin that became available for military use in early 1940's. Penicillin's therapeutic applications in the later stages of World War II was credited with saving tens of thousands of wounded that would otherwise have succumbed to bacterial infections.
History Summary (http://www.youtube.com/watch?v=iXJhu1T3XQk&feature=related)
Where we are now and Natural product discovery
Penicillin use has been widely used since the 1940’s. Penicillin or other penicillin type antibiotics: amoxicillin, ampicillin, carbenicillin, dicloxacillin, and oxacillin have been used to treat many diseases. How does Penicillin work (http://www.youtube.com/watch?v=gTWiaH_oCCY&NR=1) They have also been misused (i.e. when a patient doesn’t take the prescribed dose) or prescribed when a person has a viral infection. Antimicrobials are not effective against viruses. When to use antibiotics (http://www.youtube.com/watch?v=e5qP891fy9E)
However, with the wide spread use of antimicrobials, microorganisms have evolved and are becoming resistant to currant antimicrobial agents. This is becoming a problem for human populations. Super Bug (http://www.youtube.com/watch?v=VQhIz2LqrYA&feature=related)
The quest for new antibiotics has scientists looking to exploit natural systems to identify new compounds that can be used to by humans.
Many of the antimicrobials that are currently used are derived from Actinobacteria. Actinobacteria are a dominant group in the bacteria kingdom. Until recently, not much was know about this group of bacteria. Most were thought to be soil dwelling and free living. Remember the white bacteria growing on the leaf cutter ants that help protect the fungus garden? Those bacteria are found in the group Actinobacteria. Leaf Cutter Ants are not the only animals that are associated with Actinobacteria. Recent work has shown the sirex wood wasps, bark beetles, wasps, and honey bees are also associated with Actinobacteria. The Actinobacteria in these systems also appear to be proving protection for the host insect against pathogens much in the same they do for the ants.
Sea sponges have also become a source of novel antimicrobials. Sponges (http://www.youtube.com/watch?v=BW05vMziy2o). The sponges themselves do produce the antimicrobials, the bacteria that are associated with them do. Just as in the other examples above.
Where will look to find novel antibiotics?
How would test to see if it would be a good antibiotic?