Bacteriostatic Antibiotics And Antibacterial Drugs Biology Essay


Bacteria have survived many years being infectious and living symbiotically with humans. However, due to major outbreaks of diseases, the need to discover resistance to certain microorganisms has grown tremendously. Scientists have discovered drugs which are able to kill or slow down the growth rate of bacteria either by accident or by knowledge obtained from research. Scientists are now able to manipulate the life cycle of these bacterium to stop them from overpowering a host immune system which could ultimately lead to death. To be effective, chemotherapeutic drugs should be harmless for the host however toxic for the invading organism; the selectivity depends on the biochemical/structural differences between bacterium and the host. There is a constant germ warfare going on superficially and internally of the human body. Microorganisms have evolved to defend themselves from other types of microorganisms in the contest for nutrients and space, therefore certain chemicals excreted by different organisms have been acquire and harvested by scientist in the combat of infection.

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Certain antibiotics are bacteriostatic, meaning that they can inhibit growth of the bacteria and not kill them. This effect can only be useful if the infection has not advanced to a high enough state, in which the host immune system can still fight off the bacteria. However some antibiotics are bactericidal (e.g. penicillin) which cause bacteria to lysis. Nevertheless the function of being bacteriostatic or bactericidal is usually dose related. For example, if you lower the dose of penicillin on a patient it is likely only to be bacteriostatic. ( 1 )

Microorganisms which are sensitive to chemotherapeutic drugs are represented by a spectrum of activity. The spectrum of activity can either be narrow and broad, the broader spectrum antibiotics are usually used when there is a mixed bacterial infection or when the bacterium is unknown. However the narrow spectrum antibiotic is used for the opposite effect where an organism is known to cause the specific disease and is most effective against that particular bacterium.

There are different types of antibiotics which target different lifecycle pathways of bacteria. The discovery of antibiotics was founded by a Scottish scientist named Alexander Fleming in 1982. He showed, by accident, whilst leaving a stack of Staphylococci cultures on the bench that over a long period of time fungus had grown via contamination, and that there was a large zone where the bacteria had not grown. After examination, Fleming identified the contaminate mould on the plates as being from the genus penicillium. On the 7/03/1929 he named the substance that was released by the fungi Penicillin, after calling it "mould juice" for a few months after the discovery. "When I woke up just after dawn on September 28, 1928, I certainly didn't plan to revolutionise all medicine by discovering the world's first antibiotic, or bacteria killer" Kendall F. Haven, Marvels of Science (Libraries Unlimited, 1994) p182.

Antibacterial drugs can interfere with peptidoglycan syntheses (β-Lactam antibiotics e.g. penicillin & cephalosporin). The most important/widely used antibiotic in this category is penicillin. Penicillium chrysogenum is a mould which produces the antibacterial agent P.chrysogenum and is usually found living on the body. Penicillin antibiotics have bactericidal action as it interferes with peptidoglycan synthesis in the bacterial cell wall. The β-Lactam functional group binds to an enzyme called transpeptidase which inhibits its function of cross-linking peptide chains forming peptidoglycan which then leads to osmotic lysis. Research has shown that penicillin may stimulate these special proteins named bacterial holins, to form holes or lesions in the plasma membrane which directly leads to membrane leakage and death. (prescotts)

Antibacterial drugs can interfere with nucleic acid synthesis in bacteria, for example Metronidazole. After diffusion into the microorganism undergoes chemical modification during which chemically reactive metabolites inhibit DNA synthesis and/or damage DNA, it enters via the electron transport protein ferrodoxin. Metronidazole is active against Helicobacter pylori and several anaerobic bacteria,

Cephalosporin's have similar chemical structure and mechanism of action as penicillin as they both have a β-Lactam ring, yet they are normally not affected by penicillinase enzymes. Nevertheless, certain types of bacteria produce another type of β-lactamases known as cephalosporinase which inactivate cephalosporin. Cephalosporins are a broader antibiotic than penicillin.

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Antibacterial drugs can interfere with protein synthesis. Tetracyclines are classified as a broad spectrum antibiotic, however because of the wide use of these antibiotics there are many cases of bacterial resistance to these antibiotics. Tetracycline inhibit the binding of aminoacyl tRNA to the complex mRNA-ribosome. This is done by binding the 30s ribosomal subunit in the mRNA translation complex. Tetracycline's may be used when treating infections such as sinuses urinary tract, respiratory tract and also used to treat gonorrhea. These antibiotics are used mainly for patients allergic to β-Lactams, however like many antibiotics bacteria are slowly developing resistance to these tetracyclines.

Although antibiotics are known to treat infections, there are also dangers in using them. Antibiotics can also be the cause of infections, for example, pseudomembranous colitis. This is an infection of the colon which is due to taking a broad spectrum antibiotic such as penicillin mentioned earlier. The use of this antibiotic causes the bacteria found in the bowel to be distorted, this causes the normal flora found to be killed and thus there is a decrease in the amount of competition for space and nutrients for the other organisms. A bacterium called Clostridium difficile takes advantage of this situation and proliferates in the bowel. In addition to this it produces toxins which are responsible for diarrhea. In conclusion, the use of antibiotics should be monitored and used minimally, or only when a bacterial infection is known. Antibiotics should not be used for viral infections as this can lead to resistant strains which are now being seen by many bacteria to combat the use of antibiotics.