Determining The Minimum Inhibitory Concentration Biology

The basic construction of penicillin.The foremost two stairss in cell wall synthesis specifically the formation of acetylglucosamine to from peptidoglycan ironss, can non be inhibited by penicillin. However, in the concluding measure where the crosslinking between peptidoglycan by side peptide ironss, the penicillin inhibits this procedure. This is because penicillin has similar construction to the terminal D-alanine-D-alanine if the pentapeptide, which binds covalently to the active site of the transpeptidase enzyme ( Gorbach et al. , 2003 ) .

Chloramphenicol is another antibiotic and it has the ability to perforate though cellular membranes and be easy in battle with the bacteriums colonizing in human cells to let its antimicrobic features to take topographic point. Chloramphenicol has a simple construction and the mechanism depends on the propanoeidol mediety and dichloracetamide concatenation.

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The basic construction of chloramphenicol.What Chloromycetin does is that it inhibits protein synthesis in bacterium, nevertheless nucleic acerb synthesis in unaffected. Chloramphenicol binds reversibly to the larger 50S ribosome fractional monetary unit of the 70S ribosome. This inhibits the protein synthesis by forestalling aminioacyl-transfer RNA from attaching to the 50S binding site ( Gorbach et al. , 2003 ) .

However, it has been recorded that Chloromycetin affects the mitochondrial protein synthesis. This is because the mammalian mitochondrial protein has strong similarity to bacterial ribosome where both are of 70S, with the chondriosome of the bone marrow particularly susceptible ( Riviere & A ; Papich, 2009 ) .

Protein synthesis plays a major function in bacterial growing as there are assorted cofactors and enzymes needed for multiple metabolic tracts. Minimum repressive concentration ( MIC ) is the minimal concentration of a drug which inhibits bacterial growing, but does non kill the micro-organism. Minimum bacteriostatic concentration ( MBC ) is the minimal concentration of a drug which kills the bacterial and therefore, no longer grows.

This probe was done to find Minimum repressive Concentration ( MIC ) and the Minimum Bacteriocidal Concentration ( MBC ) of Penicillin and Chloramphenicol of Escherichia coli every bit good as ; to find the antibiotics sensitiveness against the Staphylococcus aureus and Pseudomonas aeruginosa. The methods and stuffs are as per research lab manual of Medical Microbiology BTH3722 of Monash University Semester Two, Year 2012 of pages 17 – 20.



There are two subdivisions to this probe, where there is ( I ) , the MIC and MBC finding of antibiotic Penicillin G and Chloramphenicol against Escherichia coli, and so there is ( two ) antibiotics proving towards two micro-organisms which are Staphylococcus aureus and Pseudomonas aeruginosa.

In the finding of MIC, consecutive dilutions of antibiotics are done with known concentrations. Then, each tubing incorporating different antibiotic concentration is the inoculated with bacterial civilization and incubated overnight. This goes the same for the finding of MBC. Then, for each consecutive dilution of antibiotic, there would be two control tubings, one positive where the tubing is inoculated with bacterial civilization and the incubated without antibiotics and so, negative control where the tubing is non inoculated but there ‘s presence of antibiotics.

For the antibiotic sensitiveness testing, there are two Mast rings used and both of them are ready-made device that can at the same time prove for antibiotic susceptibleness proving utilizing 8 types of antibiotics. The Mast Rings used in this probe is MAST M43 to prove against MG8 civilization: Staphylococcus aureus and MAST M14 to be used to prove against MG53 civilization: Pseudomonas aeruginosa. All these are done on the MHA home base utilizing dispersed home base technique.


The MIC and MBC for each antibiotic type ( Penicillin G and Chloramphenicol ) is determined by detecting the turbidness in the trial tubing. A cloudy medium signifies for bacteriums growing. Then all the tubings that are unfertile are so poured into several Trypticase Soy Broth ( TSB ) bottles including the tubing that has the minimal positive bacteriums growing to find the MBC. These bottles are so incubated overnight. For the antibiotic susceptibleness testing, the annulate radii of the clear zones are measured for each antibiotic type and these measurings are recorded.


The MIC and MBC value of penicillin G can non be determined as at all concentrations of the consecutive dilutions, the bacterium is immune to the Penicillin G ( PG ) even from the concentration of 125 Aµg/ml. This is because there was growing observed from the turbidness of all the consecutive dilution tubings. However for the antibiotic Chloramphenicol, the MIC is at 31.25 Aµg/ml while the MBC is at 62.6 Aµg/ml. At these concentrations, in handling infections that are E. coli related, a instead heavy dose of PG is needed to be administered.

Therefore, PG is non truly effectual in killing E. coli. Besides, the MBC value is ever expected to be higher than the MIC value is higher dose is needed to kill a micro-organism ( Prescott et al. , 2005 ) . As it has been antecedently mentioned, PG targets the peptidoglycan construction of the cell wall. If the bacteriums were able to defy PG, it would be because that the bacteriums have a mechanism to counter such actions. True plenty, E. coli could be immune to PG because it could bring forth penicillinase that inactivates penicillin ( Sorbo & A ; Marshall, 2006 ).

Beta-lactamase which is besides known as beta-lactamase, Acts of the Apostless by hydrolyzing the CO-N bond in the beta lactam ring of the penicillin molecule and so the amidase group cleaves the CO-NH bond found within the side concatenation and the six amino acid groups of penicillic acerb group of the penicillin molecule ( English et al. , 1960 ) . However, non merely E. coli is non the lone one bacterium that possesses the penicillinase cistron which can caused by the fact that certain bacteriums passed on their Deoxyribonucleic acid to another bacterium during junction, or from a virus to a bacterium during transduction or besides that the bacteriums can take in foreign Deoxyribonucleic acid from their milieus ( Karp, 2009 ) .

In the antibiotic testing on the bacteriums lawn, it is found that the Staphylococcus aureus ( S. aureus ) is less immune than Pseudomonas aeruginosa ( P. aeruginosa ) as S. aureus is susceptible to three sorts of antibiotics ( susceptible: Carbon monoxide, GM and S ; resistant: AP, KF, ST, T and TS ) compared to P. aeruginosa which is susceptible to two types ( susceptible: GM and FC ; resistant: PG, CD, SMX, T and EM ) .

The ground P. aeruginosa is so peculiarly so immune is to most of the modern antibiotics is because of its intrinsic opposition that arises from the permeableness and secondary opposition mechanisms such as energy-dependent multidrug outflow and chromosomally encoded periplasmic I?-lactamase. At such degree of natural opposition, mutational opposition to most categories of antibiotics can readily originate ( Hancock & A ; Speert, 2000 ) .

For case, the opposition of P. aeruginosa towards PG is because of de-repression of chromosomal I?-lactamase and besides the overexpression of the MexAB-OprM multidrug outflow pump due to a NalB mutant. Specific plasmid-mediated I?-lactamases besides infer that the opposition to PG could be a signifier of debut of foreign Deoxyribonucleic acid from milieus or via junction with other bacteriums ( Hancock & A ; Speert, 2000 ) .

As for S. aureus, the bacterium is immune towards Principen and that would likely due to the act that most strains of S. aureus are able to bring forth I-lactamase to breakdown the beta-lactam ring of the penicillin-derivate antibiotics.


The MIC and MBC values are of import in finding the right dose of antibiotics that is supposed to be administered to the patient. However, E. coli was peculiarly immune to Penicillin G and therefore, was unable to bring forth any MBC or MIC values. In such instances, an AST can be ran foremost before proving E. coli against its susceptible drug for MIC and MBC values.


  1. English, A.R. , McBride, T. J. and Huang, H. T. ( 1960 ) . Microbial Resistance to penicillin every bit related to penicillinase or penicillin acylase activity, Proceedings of the Society orA ExperimentalA Biology andA Medicine, Vol. 104, pp. 547 – 549.
  2. Gorbach, S.L. , Barlett, J.G. and Blacklow, N.R. ( 2003 ) .Treatment of Infectious Disease, Infectious Disease, Lippincott Williams & A ; Wilkins, pp. 184 – 186.
  3. Hancock, R. E. W. and Speert, D. P. ( 2009 ) . Antibiotic Resistance in Pseudomonas aeruginosa: mechanisms and impact on intervention, Drug Resistance Updates, 3, pp. 247 – 255.
  4. Karp, G. ( 2009 ) . The Turning Problem of Antibiotic Resistance, Cell and Molecular Biology: Concepts and Experiments, John Wiley & A ; Sons, pp. 105 – 106.
  5. Riviere, J.E. and Papich, M. G. ( 2009 ) . Chemotherapy of Microbial Diseases, Veterinary Pharmacology and Therapeutics, John Wiley & A ; Sons, pp. 944 – 946.
  6. Sorbo, L. D. and Marshall, J.C. ( 2006 ) Antibiotic Resistance in the Intensive Care Unit, Intensive Care Medicine: Annual Update 2006, Springer, pp. 582 – 583.

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