The time kill curve is used to determine the bactericidal or bacteriostatic activity of antimicrobials. It is analyzed by plotting log 10 CFU/mL versus time. A bactericidal effect can be seen by a 3 log10 decrease at the time specified. But for that, should I compare with control free antimicrobial or with first time of the same sample?
According to the definition, bactericidal activity is defined as a reduction of 99.9% (≥ 3 log10) of the total number of CFU/mL in the original inoculum (Silva et al., Journal of Antibiotics, 64(4):321-5, 2011
For FDA, bactericidal activity as a reduction of 5 log CFU compare in the original inoculum.
Many thanks, Filomena. Please let me know what is your opinion abot the following: We are going to quantitate teh antibacterial activities of cell-free conditioned media (CFCM) of microorganisms which produce strong antibacterial componds. But we cannot separate the components yet. Consequently, when we cannot speak about LC50 or LC99. Insted we introduced the torm of MID, that is Maximum Inhibitory Diluton of SCCM (Furgani et al., 2006; Böszörményi et al., 2009). Is it correct? Faithfully yours, András (Wooster, OHIO, USA).
Thanks for all your comments. Julio: can you give me some references? papers whrite about 3 or 2 log10. Good day. Fernanda Mo.
According to the CLSI guidelines, usually used for antimicrobial activity testing (CLSI. Methods for determining bactericidal activity of antimicrobial agents; approved guidelines, M26-A, vol. 19), it is a 3 log reduction
Andras, unfortunatelly I'm not familiar with the term, but when working, for instance, with plant extracts, we usually use the dilution, expressed as a percentage, like % (v/v). I don't know if the information is useful...
Yes, Filomena, it does. Many thanks. Unfortunately I could get access to Methods for determining bactericidal activity of antimicrobial agents; approved guidelines, (M26-A, vol. 19) neither in here Wooster, OH, nor in my homeland, Hungary. Would it be an absolutely inpertinent querry to ask you send me a copy as an attachemnt file to my e/mail address [email protected]? I would appreciate a lot. Your sincerely, Andras
Both healthy and infected control gropu to be kept for comparision
late reply however I think it may benefit..."Antibiotics in Laboratory Medicine" by Victor Lorian, ed.5
Hi can i ask question to this thread as well? I am doing time kill as well now, testing on combination of drug. i have problem with interpretation as for example at time 4hr, the cfu/ml goes to zero and and at 24hr the cfu rise up again. is this possible to happen for time kill assay. hope experts above can give opinion. many thanks
For cfu to go down at certain time period and go up again its normal. That shows the time efficacy of your drug against bacteria.
In your case I would suggest you repeat the test again. Do it in triplets and see the difference btw results.
Thanks. Is it true that using plastic tube will reduce the efficiency of the assay? Now i am using the falcon tube, and some paper say the bacteria may stuck in the wall of tube and that maybe the reason i got 'zero' in certain time and rise again after sometime.
Thanks for your participation Nor. Plastic tube reduce the efficience. It´s true. The reason is that some antimicrobial like oils or plant extracts adhere to the plastic walls of the tube and their effect can not be completely measured because it can´t form a homogeneous solution. I recommend using glass tubes.
Hello Dr. Fernanda, We are also performing Time Killing Curve at our laboratory for evaluation of efficacy of herbal medicine and found that absorbance @ 600 nm also can converted to Viable count.....
Calibration curve has to be plot between CFU/ml and absorbance by using nutrient broth medium and linear regression coefficient
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