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Title: Antibiotic resistance patterns in E. coli and Salmonella isolates recovered from commercially available compost

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

Submitted to: BARC Poster Day
Publication Type: Abstract Only
Publication Acceptance Date: 3/9/2010
Publication Date: 4/21/2010
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 available compost. BARC Poster Day. p.12.

Interpretive Summary:

Technical Abstract: 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 product. Since compost is often prepared from manures and biosolids from therapeutically-treated animals and humans, residual human pathogens may exhibit resistance to these antibiotics. We determined the prevalence of resistance to selected antibiotics in E. coli and Salmonella isolates from commercially available biosolids and yardwaste-based composts. Individual E. coli (n=184) and Salmonella (n=43) isolates 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. Resistance to one, two, three, four and five antibiotics was observed in 19%, 7.6%, 2.2%, 1.6% and 1.1% of E. coli isolates, respectively. For Salmonella isolates, 16.3%, 18.6%, 20.9% and 4.6% were resistant to one, two, three and four antibiotics, respectively. Source-type of compost did not affect the prevalence of antibiotic resistance profiles among E. coli; however, Salmonella was only recovered from biosolids-based compost. E. coli and Salmonella isolates were most frequently resistant to the tetracyclines (doxycycline and tetracycline) followed by the penicillins (ampicillin and amoxicillin), and aminoglycosides (streptomycin). Some commercially available composts contain low numbers of antibiotic-resistant E. coli and/or Salmonella. Use of composts in certain pre-harvest environments may constitute a contamination risk for fresh produce. Antibiotic resistance in pathogens has the potential to complicate treatment in cases of foodborne illness.