Science Buddies: "Ask an Expert"

Im testing different honeys antibacterial activity when diluted, but i dont know how to do this accurately. Should i dilute them by weight? (1gram of honey 1 gram of water gives a dilution of 50%) or should i do it by measuring the amount in ml?

Technically, you can dilute either by weight of honey/volume of water or volume of honey/volume of honey. You wouldn't measure the water by weight, though. As long as you accurately record what you did and report the solution properly there isn't any reason either wouldn't work. If you choose to dilute grams of honey/volume of water you would report your final concentration as a percent solution (weight/volume). In this type of solution, a 1% solution is defined as 1gram/100mL of water, so if you diluted 1 gram of honey in 10mL of water you would have a 10% solution (w/v). Alternatively, you can measure in volume. There if you combined 1mL of honey with 1mL of water you would get a 50% solution (1mL honey out of 2 total mL). Since honey is nominally a liquid, I would tend to do a volume/volume solution, but again, as long as you carefully note and accurately label your final solution, either one is correct.

Hope this helps and please post again in this topic if you have any further questions!
JMP

Hello there,

Another thing to think about is to make several dilutions of the different types of honey you have just so you can test the antibacterial effects of honey over a range of concentrations. For example, if your honey concentration is way too low, you may not be able to see any antibacterial effects and it may lead you to conclude that certain honeys may not be antibacterial at all. However, it is possible that if you increase the honey concentration by a bit, you would start seeing antibacterial activity. At the same time, if you test a honey concentration that is way too high, you may not even see bacterial growth at all. This would at least tell you that the honey has antibacterial activity, but would make it difficult to compare and see which honey is more effective at killing the bacteria. Making a range of dilutions will allow you to find the optimal honey concentration that can inhibit bacterial growth but at the same time allow you to compare the effectiveness between the different types of honeys you are testing.

Best of luck,
Connie

Thanks for the information! But what range of dilutions should i use when testing the antibacterial properties?

This is the sort of question best answered by a search of the literature. In the paper I am attaching below, they used a 25% dilution (w/v) of honey and saw antibacterial properties, but the effective dose will likely depend at least in part on what kind of honey and the type(s) of bacteria you are using, so feel free to look for more references that apply to your specific example. Otherwise, you could use this as a starting point.

The concentration used in the reference included in the previous message could serve as a starting point, middle point, or comparison points. It could serve as starting point, for example, if you would like to evaluate different concentrations and would like a to do a preliminary test to see if your honey does have antibacterial activity at that concentration. Could be a middle point if you would like to evaluate concentrations above and below the one used in the included reference. Finally, the concentration used could in the included reference may be used to compare different honeys at the same concentration.

The previous posters all have some really good suggestions! Personally, I would probably start with a fairly concentrated honey solution (maybe 50% if the solution doesn't become too viscous) because assuming that all honeys have some sort of antibacterial activity, starting with a higher concentration will allow you to see bacterial inhibition. If you don't see bacterial growth at all in honey-treated cultures versus untreated cultures, that would indicate that the honeys you've tested do have antibacterial effects. Now, you can then dilute down further to make less concentrated solutions to see if those still have antibacterial activity, to the point where you don't kill all of the bacteria so you can actually count the number of bacteria still alive in your culture. I think that having 25% as a reference is great, and definitely keep that in the back of your mind, but as JMP also mentioned, other honeys may not have the same antibacterial effects at that concentration, and it would be a pain having to try to dilute up/down for all the different honeys. It would probably be easier to just start at a high concentration for all of them, and then dilute them all down to the same concentrations. However, if some of your honeys still don't show significant antimicrobial activity at 50%, you can of course try an even higher concentration, but the solution may become a bit too viscous and may be difficult to add to your bacterial cultures homogeneously; it will also indicate that this particular honey has weak antimicrobial activity, if at all, compared to the one that JMP had mentioned.

Hope that helped!