Clostridium susceptibility to formic acid
Pathogenic clostridial species are associated with a host of different disease states in poultry. Probably the most well known would be necrotic enteritis (NE), which is caused by Clostridium perfringens. Usually in association with some sort of gut stressor like coccidia infection, excessively high dietary protein, or high fiber. Overall, the cost of NE to the broiler industry is estimated to be more than $5 billion globally. There are several other poultry clostridial diseases in addition to NE. For example, C. colinum causes ulcerative enteritis, C. perfringens and C. septicum both cause gangrenous dermatitis/cellulitis, and C. botulinum causes botulism.
Control of Pathogenic Clostridia
Pathogenic clostridia are collectively very difficult to kill. They are ubiquitous in the environment, and this is due in no small part to their hardiness. For example, C. botulinum has been shown to grow best between 90 and 95°F, and capable of growing anywhere between 43 and 104°F. This means conditioning and pelleting (generally done between 65 and 90°F), which is a good means of killing salmonella is quite probably working against us on clostridia. Furthermore, clostridia – much like bacillus – are spore forming bacteria. When they are faced with conditions that are no longer favorable for growth they are capable of sporulating and waiting for better days.
Fortunately, chemical interventions like acidification have been shown to be better for inhibiting clostridia. In the lab, formic acid has been shown to require as little as 0.1 to 0.15% to inhibit C. botulinum and C. perfringens (Strauss and Hayler, 2001). This is compared with 0.25 and 0.30% for propionic and lactic acid, respectively to inhibit clostridia. This is similar to the sensitivity of other microorganisms of concern (Figure 1)
Figure 1. Minimum inhibitory concentrations (MIC; lower is better) of 3 common organic acids against different microbial of concern. Adapted from Strauss and Hayler (2001).
Working in the lab is, of course, less important than working in the animal. Fortunately, acidification with formic acid has been shown to reduce clostridia and severity of associated diseases, such as NE. Manzoor et al. (2013) compared formic acid with Amprolium in birds challenged with coccidia and reported a restoration of normal body weight and improvements in NE severity with 5000 ppm of formic acid in the drinking water.
Recent work from our company has shown that Amasil NA (feed grade sodium formate) can deliver comparable benefits to feed medication with Coban (monensin; Elanco) and BMD (bacitracin methylene disalicylate; Zoetis) in birds challenged with coccidia and C. perfringens (Coelho et al., 2019a,b) in terms of both performance and NE severity.
Clostridium perfringens at day 21 and 42 of age. Points within a graph with different superscripts are different (P < 0.05). Scoring was done on a 0 to +4 scale according to Johnson and Reid (1970). Score 0 = no gross lesions; +1 = very few scatter petechiae on the cecal wall, no thickening of the cecal walls, and normal cecal contents present; lesions more numerous with noticeable blood in the cecal contents, cecal wall is somewhat thickened, and normal ceceal contents present.
Acid tolerance response
When using organic acids to control clostridial species, it’s important to ensure that you apply strong and consistent pH pressure. This is because acid tolerance response. When subjected to a sub-lethal pH challenge (say pH of 4.5) they turn on genes that enable them to survive a stronger subsequent challenge that would have otherwise have been lethal (say pH 3.5; Villarreal et al., 2000). This is where use of a strong organic acid like formic comes in hand. Many other organic acids are simply not capable of achieving a low enough pH to kill clostridia, but they are capable of achieving a pH that triggers the acid tolerance response. This then poses a problem for the birds themselves, as well as the food safety system that relies heavily on acids for pH control and pathogen control in meat processing.
Unfortunately, the story around clostridium is not so simple as “Clostridium = BAD”. While all the species outlined above are toxin producing proteolytic clostridial species, there also exist several commensal clostridial species in the bird. Commensal clostridia are generally saccharaolytic clostridial species (clusters IV and XIVa). Several such strains have been identified that can convert acetate to butyrate in the gut and intestinal butyrate is widely recognized as beneficial to gut health and intestinal integrity. Therefore, it’s important to focus on controlling the ‘bad’ clostridia at feed intake without necessarily eliminating all beneficial species that have colonized the gut. Acidification can be a potent tool toward that end, but it is important to use efficient organic acids consistently to ensure best effect.
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By Joshua A. Jendza, firstname.lastname@example.org