This Is AuburnElectronic Theses and Dissertations

The use of Bacillus subtilis as a direct-fed microbial and its effects on production and colonization of Salmonella Enteritidis and Clostridium perfringens in production broilers




Frazier, Anthony Nathan

Type of Degree

Master's Thesis


Poultry Science


The growing emergence of antimicrobial resistant bacteria has given rise to consumer fear that the use antibiotics in the meat industry can lead to more antimicrobial resistant strains. Because of this fear, the poultry industry is moving away from using antibiotics and antibiotic growth promoters (APG) in production birds. However, removing antibiotic therapy in treating disease can lead to an increase in pathogenic bacteria. Alternative methods to antibiotic therapy are currently being explored. One alternative method being research is the use of direct-fed microbials (DFM), also known as probiotics. Probiotics have been in use for several decades but their exact modes of action have yet to be identified. DFMs in the diet of production birds are thought to be production enhancers as they are capable of promoting beneficial bacteria within the microflora. The use of probiotics in commercial broilers has been shown to provide an intestinal ecosystem that benefits the bird by inhibiting the growth and colonization of pathogenic bacteria, such as Salmonella and Clostridium perfringens. It has been suggested that the use Bacillus subtilis, a common soil bacterium, could improve growth performance as well as improve feed conversions in broilers. One important characteristic of Bacillus subtilis that makes it a viable prospect as a DFM is the ability to produce endospores. These endospores are capable of withstanding inhospitable environments meaning Bacillus subtilis endospores are capable of surviving the feed-milling procedure. The objective of this study was to determine the viability of seven isolates of soil-origin Bacillus subtilis as a direct-fed microbial in production broilers and determine their ability to inhibit the growth of the pathogenic bacteria Salmonella Enteritidis and Clostridium perfringens. The isolates used were designated AP71, AB01, AP302, AP183, AP185, AP206 and AP294. Isolates AP71 and AB01 were found to be inconclusive in inhibiting the colonization of Salmonella Enteritidis in male broilers. A screening trial provided insight into the ability of the seven isolates of Bacillus subtilis in inhibiting the growth of Clostridium perfringens. AP302, AB01, AP206 and AP183 were found to be able to significantly inhibit the growth of Clostridium perfringens. These isolates were utilized in a bird trial and were found to not be able to significantly increase the performance of the birds or significantly inhibit the growth of Clostridium perfringens. More research should be done in order to determine the efficacy of these isolates as a DFM.