Date of Award
Master of Science (MS)
Henson , Michael
Tzeng , Tzuen-Rong
Over the last few decades there has been an increase in the use of organic fertilizers due to the rise in popularity of organic food production. However, if the fertilizers are not adequately sanitized there is the possibility of contamination of agricultural crops by foodborne pathogens from the spreading of organic fertilizers onto the crops. This is especially important for animal waste-based fertilizers since animals frequently carry foodborne pathogens. Furthermore, antibiotic use in food animal production may induce antimicrobial resistance in gut bacteria which can be spread to crops and the environment through fertilizer use. The objectives of this study were to analyze various organic fertilizers for microbial quality and the presence of antimicrobial resistance as well as evaluate the growth potential of foodborne pathogens in selected fertilizers.
One hundred and three organic fertilizer samples were surveyed for moisture content, water activity, pH and microbial quality, including enumeration of total bacteria count, Enterobacteriaceae, total coliforms, and Escherichia coli as well as the presence of foodborne pathogens Salmonella, Escherichia coli O157:H7 and Listeria monocytogenes. Moisture content ranged from 0.98% to 86.37% with the water activities between 0.298 and 0.999 and the pH between 3 and 10 with an average of 7.77 ± 1.28.Total bacteria, Enterobacteriaceae, coliforms, and E. coli were in the range of 3 to 9, <1 to 7, <1 to 6, and <1 to 6 log CFU/g, respectively. No Salmonella, E. coli O157:H7, or L. monocytogenes were found.
The growth potential of Salmonella spp. and E. coli O157:H7 was evaluated in selected organic fertilizers with high (≥5 log CFU/g) and low (<5 log CFU/g) levels of background bacteria. In fertilizers with high levels of background bacteria, Salmonella and E. coli O157:H7 increased ca. 1 log CFU/g in plant-based compost and fish emulsion-based compost, respectively. In fertilizers with low levels of background bacteria, pathogen growth was observed in bone, blood, and feather meal and the mixed source fertilizer by ca. 3 and 4 log CFU/g for Salmonella and E. coli O157:H7, respectively.
E. coli isolates (n=72) from organic fertilizers were further characterized for phylogenetic group, the presence of shiga-toxins, resistance to antibiotics and presence of integrons. All of the isolates were negative for shiga-toxins (stx1 and stx2). The majority of the isolates belonged to phylogenetic group B1 followed by group A. Eleven isolates had antimicrobial resistance with five resistant to ≥2 antibiotics and two resistant to ≥10 antibiotics. Five of the eleven isolates had class 1 integrons present.
In conclusion, our study revealed a wide range of microbiological quality among organic fertilizers, and identified some factors affecting the growth of foodborne pathogens in these fertilizers.
Miller, Cortney, "MICROBIOLOGICAL SAFETY OF ORGANIC FERTILIZERS USED FOR PRODUCE PRODUCTION" (2011). All Theses. 1123.