Re: Article - An update on the use of acidifiers in piglet diets

This is an excellent article indeed.

However, I wish to point out to the author that he may have made a mistake. First, he stated that formic acid appears to be primarily effective against yeasts and some bacteria such as E. coli and Salmonella.

He then quotes acetic acid as an example, stating that it inhibits the growth of several species of bacteria but is less effective on yeasts and moulds. As for propionic acid, he states that it is usually targeted at moulds but has a reduced efficacy against bacteria and none against yeasts.

So how then can the Minimum Inhibitory Concentration (MIC) of formic acid against E. coli be five times higher than that of acetic and propionic acid, if formic acid is supposed to be primarily effective against E. coli, while propionic acid is supposed to have reduced efficacy against bacteria?

MIC is supposed to be the lowest concentration of an antimicrobial that will inhibit the visible growth of a microorganism after overnight incubation. So the higher the MIC, the less efficacious the substance is as an antimicrobial.

So to me, this is a contradiction and a paradox.

I hope the author will explain this in greater detail.

Thanks!

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Re: Article - An update on the use of acidifiers in piglet diets

Dear Dr Tan

Thank you for your positive comments and thank you for pointing out the mistake in my article. Indeed you are right that there is a contradiction in what was written.

The correct sentence should have been: As a comparison, the MIC of formic acid against E. coli is five times lower than of acetic and propionic acid.

This is just a typing mistake and I cannot blame the secretary since I wrote this article myself... Let me just apologize for that mistake.

Regarding the five times lower we could also discuss the validity of this statement. As you certainly know MIC will depend on the protocol that is used, and especially on the original pH of the environment. The pH will affect the rate of dissociation of each acid (depending on their pKa value) and therefore will also have an impact on their MIC. This is why antibacterial effect of the organic acids can be variable depending on the buffer capacity of the feed.

Thanks again for spending some time to read carefully this article.

Best regards

Mathieu Cortyl

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Re: Article - An update on the use of acidifiers in piglet diets

Nice article.. Just to know, what are the chances of resistance development against these acids, in due course of time, particularly wrt E. coli and Salmonella?

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Re: Article - An update on the use of acidifiers in piglet diets

Dear Dr. Puneet Agrawal

Thanks for your question and sorry for the time taken to reply, but I was enjoying my summer vacation!

Some researchers have demonstrated the existence of an adaptive response to acidity for some pathogenic bacteria. This phenomenom is called acid tolerance response (ATR). However, this is not a resistance to the acids, but an adaptation to the acidic environment. For this ATR to happen, the bacteria must first encounter mildly acidic conditions for a certain time, after which it will be able to produced the so-called acid shock proteins (ASP). The ASP will help the bacteria to better survive acidic conditions.

To summarize, the bacteria needs to adapt itself to mild acidic conditions before it can survive under acidic conditions. This means we should avoid using acidifiers at low dose, with for instance the objective to reduce the cost of the feed additive.

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