Dissertation/Thesis Abstract

Antimicrobial Effects of Organic Acids and Their Derivatives
by Kovanda, Lauren, M.S., University of California, Davis, 2020, 85; 28090190
Abstract (Summary)

The benefits of dietary organic acids have been utilized for decades to increase the shelf life of animal feed and promote animal growth and health. As products of fiber fermentation, or components in biological sources such as milk, organic acids are natural antimicrobial compounds. Since the 1930s, humans have administered antibiotics to prevent and treat bacterial infections in humans and animals. Although antibiotics were revolutionary and contributed to our success, they lose efficacy over time due to antibiotic resistance in bacteria. The development of antibiotic resistance has occurred naturally over millennia and is exacerbated by the misuse and/or overuse of antibiotics in humans and animals. The use of in-feed antibiotics for animal growth promotion in the United States has been banned since 2017. Livestock animals had received various protections and health benefits by consuming in-feed antibiotics or antimicrobial growth promoters (AGPs) prior to their banning. Therefore, research on the beneficial effects of non-antibiotic feed additives is increasing in order to potentially replace the growth-promoting effects and health benefits observed when fed AGPs is needed. To address this need, the aim of this experiment was to evaluate the potential of using organic acids and their derivatives as alternative antibiotic feed additives to promote animal growth. The selected organic acids, including butyric acid, valeric acid, propionate glycerides, butyrate glycerides, valerate glycerides, monolaurin, sodium formate, and ProPhorce, a mixture of sodium formate and formic acid (40:60 w/v), were tested at 8 to 16 concentrations from 10 to 50,000 mg/L. Their minimum inhibitory concentrations (MICs) for Gram-negative bacteria (Escherichia coli, Salmonella Typhimurium, and Campylobacter jejuni) and Gram-positive bacteria (Enterococcus faecalis, Clostridium perfringens, Streptococcus pneumoniae, and Streptococcus suis) were evaluated using the micro-broth dilution method (in vitro; Stoddard et al., 2008; Li et al., 2014; Li et al., 2015). The MICs of butyric acid, valeric acid, and ProPhorce varied among bacterial strains with the lowest MIC of 500 mg/L for two strains of Campylobacter. Sodium formate at highest tested concentrations (20,000 mg/L) did not inhibit the growth of Escherichia coli, Salmonella Typhimurium, and Enterococcus faecalis, but sodium formate inhibited the growth of other tested bacteria with MIC values from 2,000 to 18,800 mg/L. The MIC values of valerate glycerides, monolaurin, and butyrate glycerides ranged from 2,500 to 15,000 mg/L against the majority of bacterial strains. Propionate glycerides did not inhibit the growth of all investigated bacteria with the exception that the MIC of propionate glycerides was 11,300 mg/L on Clostridia perfringens. Monolaurin strongly inhibited Gram-positive bacteria with the MIC value of 10 mg/L against Streptococcus pneumoniae, and 300 mg/L against Clostridium perfringens. The MIC results indicate that organic acids and their derivatives exhibit promising antimicrobial effects in vitro against Gram-negative and Gram-positive bacteria that are resistant to antibiotics. Monoglyceride derivatives are inhibitory, although they may be less effective compared with their free fatty acid forms. In particular, medium chain fatty acid ester, monolaurin, exhibited very strong inhibitory effect on Gram-positive bacteria. In summary, this study suggests that certain organic acids and their derivatives have promising antimicrobial properties and are candidates for partially replacing antibiotics in feed. Future in vivo research will be needed in order to determine their benefits on promoting the overall health and performance in pig and poultry.

Indexing (document details)
Advisor: Liu, Yanhong
Commitee: Yang, Xiang, Wang, Luxin
School: University of California, Davis
Department: Animal Biology
School Location: United States -- California
Source: MAI 82/5(E), Masters Abstracts International
Source Type: DISSERTATION
Subjects: Microbiology, Nutrition, Animal sciences, Range management, Pathology
Keywords: Antibiotics, Gram-negative bacteria, Gram-positive bacteria, Minimum inhibitory concentration, Organic acids, In vitro, In vivo
Publication Number: 28090190
ISBN: 9798691213687
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