Pathogen-inhibiting activity of commercial organic acids

Growing concerns over resistance to antibiotics in pathogenic bacteria has resulted in increasing public and government pressure to reduce the use of antimicrobial growth promoters (AGPs) in animal feed. A negative result of AGPs removal is potential increase in incidence of certain diseases in poultry, such as necrotic enteritis and avian salmonellosis.

Among the proposed antimicrobial alternatives to antibiotics are organic acids such as propionic and formic acid. Propionic acid is mainly used as preservatives for feed, whereas formic acid is mainly used to improve nutrition and health in animals. A combination of different alternatives to antibiotic may hold the most promising method to substitute antibiotics in animal feeds.

Experimental protocol

The antibacterial activities of Novibac CF 60 against C. perfringens, Salmonella typhimurium and Escherichia coli isolated from the intestine of chickens were studied in-vitro. The spray dried free flowing mixture of calcium formate, calcium propionate and citric acid, from Innovad, Belgium was added at different concentrations (ranging from 600 to 4200 mg/kg) to a media inoculated with C. perfringens, S. Typhimurium and E. coli.

The antimicrobial susceptibility testing was performed using the broth microdilution assay based on the ISO 10932/IDF 223 standard protocol. Bacterial growth was verified by measuring the OD at 580nm and the minimal inhibitory concentrations were determined.

Bacterial growth inhibited

Novibac CF 60 effectively inhibited the growth of these 3 bacteria. The most susceptible organisms were S. Typhimurium and E. coli, with MICs of 3000 mg/kg, followed by C. perfringens with MIC of 4200 mg/kg. The mechanism of this beneficial effect was attributed to the ability of these acids to pass across the cell membrane of the bacteria, dissociate in the more alkaline interior and acidify the cell cytoplasm.

However, these results show that the product, at a low concentration (less than 2000 ppm) increase the growth of S. Typhimurium and E. coli. It can be hypothesised that organic acids at low concentration serve as a carbon source for the endogenous microbiota and at high concentration can exhibit toxic effects on bacteria.

Benefits to the gut microflora

These results suggest that using the product at the recommended dose of 3000 ppm act as preservatives for grains or feed and have a potential role in beneficially altering gut microflora by reducing pathogenic bacteria.

In conclusion, the susceptibility data obtained in this study provides strong support for the claim that Novibac CF 60 is an effective treatment for a range of infectious bacteria in feed and animal.

Author: Dr Alireza Khadem, University of Ghent