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Determination of MIC and MBC of selected tetracycline capsule
commercially available in Bangladesh
Kowser MM1, Hoque MM2, Fatema N3
The ORION Medical Journal 2009 Sep;32(3):684-686
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Abstract

Background: Usually we consider that the tetracycline capsules in Bangladesh maintain standard MIC and MBC. But how much is this assumption is true? this will be evaluated through this research work. Objective: This is a cross sectional study (January-2006 to Decmber-2006) to determine the minimal inhibitory concentration (MIC) and minimal bactericidal concentration (MBC) of tetracycline capsule commercially available in Bangladesh.Method: The collected samples were analyzed according to BP specifications. The MIC was determined by broth dilution method. MBC were determined by the drop plate method from the tubes, where apparently no visible growth found. Results: The MIC value of tetracycline capsule against Bacillus pumillus, Pseudomonus spp.  Staphylococcus aureus, Shigella spp. and E coli were found 1.0, 8.0, 0.5, 1.0 and > 64.0  mg/ml (micro gram per milliliter) respectively. The MBC value of tetracycline capsule against Bacillus pumillus, Pseudomonus spp. Staphylococcus aureus, Shigella spp. and E coli were found 2.0, 16.0, 1.0, 2.0 and > 64.0 mg/ml respectively. Conclusion: MIC and MBC values higher than that of the peak serum concentration must have chance of therapeutic failure and development of antibiotic tolerance and resistance to the bacteria.

Key words
Minimal inhibitory concentration (MIC),  Minimal bactericidal concentration (MBC), Colony forming unit (C.F.U).

Introduction
To evaluate the efficiency of antibiotic there are two factors1, which influence potential utility of a antibiotic in a specific clinical situation. The first is the measure of potency of the antibiotic for the pathogen in question MIC and MBC. The second is relationship between the concentration time profile and potency of the antibiotic. This research work will play an important role to determine the MIC and MBC of selected tetracycline capsule in Bangladesh.

Materials and methods
1. Collection of sample: The tetracycline capsule collected from the retail seller and standard sample collected from the pharmaceutical company in the Dhaka city.
2. Collection of organisms: Pseudomonus spp. Staphylococcus aureus, Shigella spp. and E coli collected from the patient sample of Dhaka Medical College Hospital and Bacillus pumillus from the Microbiology Department of University of  Dhaka.
Reagents
1. Sterile water                 2. Hydrochloric acid
3. Potassium phosphate buffer (0.5M)
Media
1. Mueller Hinton Broth (MHB)              2. Mueller Hinton Agar (MHA)
3. S.S  Agar                                         4. Mannitol Salt Agar (MSA)
5. Cetrimite Agar (CA)                          6. Blood Agar (BA)

Instruments and apparatus
  1. Sterile 5 ml screw cap test tubes
  2. 250 ml conical flask
  3. 250 ml measuring cylinder
  4. Inoculating loop
  5. 1 ml and 0.1 ml micro pipette
  6. 10 ml glass pipette
  7. Beaker
  8. Marker
  9. Bunsen burner
  10. Small and large (7"x 7") petriplate
  11. Voltex mixture machine (FISONS-11777)
  12. Shaking or rotator machine (FISONS-200)
  13. Electrical digital balance (AJ 150 L)
  14. Spatula
  15. pH meter (HANNA)
  16. Laminar air flow (C-901)
  17. Incubator adjuster at 370C. (SLI-600)
  18. Spectrophtometer (Spectronic-20)
  19. Freeze (MDF-U20806)
  20. Micropepette (GILSON)
  21. Autoclave (HA-240M)

Preparation of tetracycline solution2
128 mg equivalent 330x128÷ 250=168.96 mg tetracycline hydrochloride (G-tetracycline) capsule was dissolved in 1000 ml sterile water and rotated at the rate of 75 rpm for 60 minute at room temperature.

MIC and MBC determination procedure
Culture: Overnight Mueller Hinton broth cultures of Staphylococcus aureus, E. coli, Bacillus pumillus, Shigella spp. and Pseudomonas spp. at 370C were prepaered. The culture was adjusted to obtain turbidity comparable to that of the turbidity of MC, Farland 0.5 standard and then further diluted 1:200 in Mueller Hinton broth. The inoculums thus prepared expected to obtain 105 to106 C.F.U/ml.
Procedure3
1. An appropriate amount of tetracycline capsule was dissolved in respective solvent to prepare an antibiotic solution containing 128 mg/ml (0.128 g drug plus 1000 ml respective solvent).
2. Two fold dilutions of the antibiotic solution in Mueller Hinton broth were prepared and described below:
   (a)  Ten sterile tubes were placed in a rack and were labeled each 1 through 8 and first one labeled as A.C (antibiotic control) and last one was labeled as G.C         (growth control).
   (b) 1 ml of Mueller Hinton broth was added in each test tube.
   (c) 1 ml of antibiotic solution was added to test tube no 1 and A.C.
   (d) With a sterile micropipette and tips, after adequate

 

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  1. Dr. Md. Mohsin Kowser MBBS , MPH , MPhil
    Associate Professor of Microbiology
    Moulana Bhasani Medical College, Uttra
    e-mail:dr.mohsinkowser@yahoo.com
  2. Dr. Md. Mahfuzul Hoque,Ph D
    Professor of Microbiology, University of Dhaka
  3. Dr. Nargis Fatema, MBBS,MPhil
    Ex. Assistant Professor,TMMC & H
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Volume 32,Issue 3,September 2009