Analyzing Indicator Microorganisms, Antibiotic ResistantEscherichia coli, and Regrowth Potential of Foodborne Pathogens in Various Organic Fertilizers

Abstract

This study analyzed various organic fertilizers for indicator microorganisms, pathogens, and antibiotic-resistant Escherichia coli, and evaluated the growth potential of E. coli O157:H7 and Salmonella in fertilizers. A microbiological survey was conducted on 103 organic fertilizers from across the United States. Moisture content ranged from approximately 1% to 86.4%, and the average pH was 7.77. The total aerobic mesophiles ranged from approximately 3 to 9 log colony-forming units (CFU)/g. Enterobacteriaceae populations were in the range of <1 to approximately 7 log CFU/g, while coliform levels varied from <1 to approximately 6 log CFU/g. Thirty samples (29%) were positive for E. coli, with levels reaching approximately 6 log CFU/g. There were no confirmed positives for E. coli O157:H7, Salmonella, or Listeria monocytogenes. The majority of E. coli isolates (n=73), confirmed by glutamate decarboxylase (gad) PCR, were from group B1 (48%) and group A (32%). Resistance to 16 antibiotics was examined for 73 E. coli isolates, with 11 isolates having resistance to at least one antibiotic, 5 isolates to ≥ 2 antibiotics, and 2 isolates to ≥ 10 antibiotics. In the presence of high levels of background aerobic mesophiles, Salmonella and E. coli O157:H7 grew approximately 1 log CFU/g within 1 day of incubation in plant-based compost and fish emulsion-based compost, respectively. With low levels of background aerobic mesophiles, Salmonella grew approximately 2.6, 3.0, 3.0, and 3.2 log CFU/g in blood, bone, and feather meals and the mixed-source fertilizer, respectively, whereas E. coli O157:H7 grew approximately 4.6, 4.0, 4.0, and 4.8 log CFU/g, respectively. Our results revealed that the microbiological quality of organic fertilizers varies greatly, with some fertilizers containing antibiotic resistant E. coli and a few supporting the growth of foodborne pathogens after reintroduction into the fertilizer.

Organic Cultivation of Tomato in India with Recycled Slaughterhouse Wastes: Evaluation of Fertilizer and Fruit Safety

“…Initially 5.65 ± 0.38 log CFU mL −1 fecal coliforms were counted before processing of BBRDM. The number decreased to 1.26 ± 0.18 log CFU mL −1 after processing, while 1.16 ± 0.08 log CFU mL [11] and not regarded as pathogens [24]. Fecal coliforms may be considered as useful indicators of organic fertilizer hygiene [8].…”

“…In this study, heat treatment of BBRDM was adequate to prevent re-growth of Salmonella after 60 days of storage. Most organic fertilizers analyzed in the study of Miller et al (2013) [24] went through some types of heat treatment, such as thermophilic composting, dry-heat and boiling. Therefore, the finished organic fertilizers had very low levels of potential pathogens.…”

“…Therefore, the finished organic fertilizers had very low levels of potential pathogens. The survey of Miller et al (2013) [24] found 28% of organic fertilizers sampled to be positive for E. coli. However, none of organic fertilizer samples analyzed by the authors [24] were positive for Salmonella and E. coli O157:H7.…”

“…The survey of Miller et al (2013) [24] found 28% of organic fertilizers sampled to be positive for E. coli. However, none of organic fertilizer samples analyzed by the authors [24] were positive for Salmonella and E. coli O157:H7. Mycobacterium bovis causes bovine tuberculosis, a chronic disease of cattle [11].…”

Organic Fertilizers: Public Health Intricacies

“…The concept of organic fertilization is ever worthwhile, with combined considerations of the public health intricacies that cannot be overemphasized [6]. Several alternative treatment methods can be employed to stabilize the organic fertilizers before use and at the same time reduce the concentrations of potential pathogens, thereby the risks.…”