A Review Of Antibiotic Resistance Biology Essay


Many antibiotics have been discovered and used for both the benefit of people as well as animals. The discovery of antibiotics was one of the most important discoveries in the history of medicine to treat fatal diseases. Bacteria have become resistant to drugs because of their overuse and this has now become an issue now that certain diseases cannot be treated as well as before. Initially these bacteria would be killed by antibiotics but they now resist their effectiveness and no longer work as before.

Paul Erlich and Alexander Fleming performed a lot of experiments and found out that certain chemicals can be used to kill bacteria without harming the host. The mechanism of inhibition is called antibiosis.1 The term antibiotic come from a Greek word anti(against) and bios(life), which is a substance produced in small amounts by microorganisms that inhibit the growth or kill other microorganisms. Antibiotics either affect the broad range of gram positive and gram negative bacteria therefore named broad-spectrum antibiotics or affect a narrow range and named narrow spectrum antibiotics.

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Antibiotics fall under antimicrobial drugs which are either bactericidal- they kill microbes, or bacteriostatic- they inhibit the growth of microbes. These drugs are effective against microbes and normal micro biota that may be present throughout the body; oral cavity, eyes, skin, stomach, intestine etc. Antibiotics are effective in the following ways; inhibit cell wall synthesis, inhibit protein synthesis, inhibit nucleic acid synthesis, and injure the plasma membrane of bacteria. They do not fight against infections caused by viruses like cold and flu but are against bacterial infections and should be taken until they are finished even though you are not feeling sick anymore. These drugs help the body’s immune system to fight off pathogens more easily so that they do not overpower your body’s defence.

The following are the antibiotics used in this experiment to compare drug susceptibilities of throat bacteria:

Erythromycin: This drug inhibits the growth or kills sensitive bacteria by reducing the production of proteins needed for the bacteria to survive.3 It is used to treat bronchitis, diphtheria, legion disease, pertussis, pneumonia, rheumatic fever and to prevent infection before surgery. Usually comes as a capsule, tablet, liquid form or as drops and it is taken after every six hours until the prescriptions is over, even after feeling well. Side effects may include upset stomach, diarrhoea and vomiting.

Ampicillin: part of the penicillin group used to treat ear infections, bladder infections, pneumonia, gonorrhoea, E.coli and salmonella infections.2 This drug should not be taken if you are allergic to penicillin antibiotics and can make birth control pills less effective. Side effects of ampicillin include upset stomach, diarrhoea, vomiting and fever.

Levofloxacin: used to prevent anthrax and plague. Pain, swelling, inflammation and breakage of tendons can be treated by this drug in the elderly. These may occur in patients who had transplants of the liver, heart or kidney. Possible side effects include constipation, dizziness, diarrhoea and nausea.

Oxacillin: penicillinase-resistant β-lactam that falls under penicillins and is a narrow spectrum drug. It is similar to methicillin and has replaced it in clinical use and it is resistant to penicillinase.4 It is used to treat bacteria such as staphylococcus but should not be used on patients allergic to penicillins. Its side effects may include fever, severe headache and sore throat as well as a red skin rash.

There will be two groups, one will investigate the antibiotic resistance of bacteria from a throat sample from students residing in MGI campus and the other group investigate samples from students residing off campus.


These results are from samples taken from MGI residents. As seen on the results of plating out of samples, the bacteria from the throat grew but the type and morphology was not known yet. Both plates showed growth which indicates that there are bacteria in throat. The microorganisms that are mostly found in the throat include streptococci, staphylococci, hemophilus bacteria, yeasts and gram-negative rods.5

The four-way streak method was performed from the cultured plates to obtain isolated colonies. Diagram2 shows the isolated colonies from both prospects, plate1 and plate2, who stay in MGI residence. Diagram3 shows the gram stain of both prospects. Both stains were gram-positive and staphylococci. The bacteria stain appeared blue because when performing the stain, the crystal violet was not washed away by the decolourizing alcohol. Gram-positive bacteria are different from gram-negative in that the chemical and physical properties of their cell walls differ. Gram-negatives have thin walls of very few layers of peptidoglycan and a lipid membrane. Gram+ have large peptidoglycan cell walls making them retain or absorb the crystal violet therefore appearing blue under a light microscope. A counter stain (safrinin) is used to colour gram negatives pink or red therefore appearing as mentioned.

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The Kirby Bauer test was performed and as noticed on diagram4, the zone of inhibition was measured. Levoflaxocin yielded the largest zone of inhibition in both plates followed by by erythromycin. The bacteria were resistant to oxacillin in plate 1 and to erythromycin in plate 2. According to the results in table1, staphylococcus are inhibited by levoflaxocin the most. Levoflaxocin can be used as an antibiotic against diphtheria and strep throat. The throat culture tests show that it is more effective than ampicillin, oxacillin and erythromycin.

Looking at table2, erythromycin is the most effective when it comes to susceptibility and oxacillin is the intermediate drug. Most bacterial samples taken off campus are resistant to ampicillin and it is also the lowest intermediate. Table3 shows the results of plate2 and ampicillin appears to be the most effective in terms of susceptibility. Levoflaxocin and oxacillin indicate the same results in the intermediate range as they fall between resistant and susceptible. Of the two plates, bacteria are more resistant to ampicillin and on average oxacillin are in the intermediate range. Microorganisms seem to be more susceptible erythromycin in off campus samples, table4&5 show that ampicillin is the least effective against pathogens in the throat. Ampicillin also has the largest number of resistant plates, 6 and 7 respectively, in resident samples. The most effective drug is levoflaxocin with a combined susceptible number of 35 in both plates.

Graph1 shows the results of samples off campus and indicates that bacteria are more susceptible to oxacillin that the other and levoflaxocin is the second best drug. Bacteria are more resistant to ampicillin. Graph 2 show that the bacteria from students who are MGI residents are more susceptible to levoflaxocin and more resistant to ampicillin. It is widely known that ampicillin is one of the best medicines to treat a sore throat but the results obtained from this investigation oppose that statement. Most of the antibiotics that would treat a throat infection are found to be in the penicillin group and if someone is allergic to these then using the drugs mentioned above is not recommended. Viral throat infections are more common but they are less severe and do not need antibiotics.6


Microorganisms from the throat are more susceptible to levoflaxocin and oxacillin. Ampicillin has developed a resistance to bacteria. This might be because of continuous use of the drug as it may be present in most medication. Both samples from residence and off campus resist from ampicillin. Antibiotics are important in treating diseases but their misuse can result in their ineffectiveness. Once a bacterium is resistant to a drug, the drug will have no effect if taken in case of an illness. One of the other reasons is that people do not complete their antibiotic prescription or even let other people use their medication after feeling well. In this experiment I have learned that antibiotics should not be use to treat viral infections such as the common cold and flu. If you are taking an antibiotic treatment, you should complete it even if you are feeling well.