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United States Department of Agriculture

Agricultural Research Service

Research Project: MICROBIAL ECOLOGY AND SAFETY OF FRESH ON-FARM ORGANICALLY GROWN PRODUCE Title: Antibiotic resistance patterns in E. coli and Salmonella isolates recovered from commercially vailable compost

Authors
item Ferguson, Sean
item Roberts, Cheryl
item Ingram, David
item Millner, Patricia
item Sharma, Manan

Submitted to: International Association for Food Protection Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: March 9, 2010
Publication Date: August 1, 2010
Citation: Ferguson, S.E., Mudd, C.L., Ingram, D.T., Millner, P.D., Sharma, M. 2010. Antibiotic resistance patterns in E. coli and Salmonella isolates recovered from commercially vailable compost. [abstract]. International Association for Food Protection Proceedings. p.91.

Technical Abstract: Introduction: Compost is used by both conventional and organic farming practices as an eco-friendly means to enhance soil properties and to reduce fertilizer inputs. Inadequate composting may lead to residual human pathogens (e.g. Escherichia coli O157:H7 and Salmonella spp.) in the final compost product. Since compost is often prepared from manures and/or biosolids from therapeutically treated animals and humans, it is possible that residual human pathogens may become resistant to these antibiotics. Purpose: We determined the extent to which E. coli and Salmonella isolates from commercially available biosolids-based and yardwaste-based compost samples were resistant to selected antibiotics. Methods: Individual E. coli (n=184) and Salmonella (n=43) isolates, previously quantified and confirmed using standard MPN and biochemical techniques, were selected from composts obtained from eight commercial operations (four yardwaste and four biosolids-based) across the U.S. For each isolate, the Kirby Bauer method was used to determine antibiograms to the following antibiotics (n=14): amoxicillin/clavulinic acid, ampicillin, chloramphenicol, ciprofloxacin, doxycycline, erythromycin, kanamycin, nalidixic acid, novobiocin, oxytetracycline, rifampin, streptomycin, sulfamethoxazole/trimethoprim, and tetracycline. All assays were performed in duplicate. Results: Overall, antibiotic resistance to one or more antibiotics was observed in 31.5% (58 of 184) of the E. coli isolates. Resistance was seen in 7.6%, 2.2%, 1.6% and 1.1% of the E. coli isolates to two, three, four and five antibiotics, respectively. For the Salmonella isolates, 60.5% (26 of 43) were resistant to one or more antibiotics with 4.7% of the isolates being resistant to four antibiotics. E. coli and Salmonella isolates were most frequently resistant to tetracycline, followed by ampicillin and doxycycline. Yard-waste and biosolids-based compost appear equally susceptible for the contamination of antibiotic resistant E. coli. Significance: We present the first study to report the existence of antibiotic-resistant E. coli and Salmonella in commercially available compost. This research suggests the possibility that compost may be a vector for the introduction of antibiotic-resistant E. coli and Salmonella into the pre-harvest environment. Use of compost that contains antibiotic-resistant E. coli and Salmonella has the potential to contaminate food crops in which it is used, and to exacerbate foodborne infections in which antibiotic treatment may be required.

Last Modified: 8/30/2014