Purpose: The purpose of this study was to identify antibiotic resistance profiles of S. Newport isolates recovered from irrigation water and poultry litter amended soil on ESV.
Methods: Salmonella spp. were isolated from irrigation ponds and wells of four vegetable farms and 14 farms fertilized with chicken manure on ESV in 2015. Antimicrobial susceptibility of 301 isolates from irrigation ponds (171), irrigation wells or creeks (49), and soils (81), was tested using 96-well Sensititer Gram Negative Narms Plates (Thermo Fisher Scientific, Waltham, MA). Antibiotic-resistant strains were defined according to the National Committee for Clinical and Laboratory Standards criteria.
Results: Of the 301 Salmonella isolates, 19.0% (n=57) were resistant to at least one of the tested antibiotics, including 10 isolates from pond water, 4 from well/creek water, and 43 from soil samples. Tested isolates were resistant to tetracycline (n=39; 13%), streptomycin (n=10; 3%), ceftriaxone (n=7, 2%), ampicillin (n=4, 1.3%), amoxicillin/clavulanic acid 2:1 (n=3; 1%), and cefoxitin (n=1, 0.3%). Seven isolates (2%) were resistant to two antibiotics, mostly tetracycline and streptomycin. Four isolates (1.3%) were resistant to more than two antibiotics; these isolates, recovered from chicken manure amended soils, were resistant to 3-7 antibiotics.
Significance: The varying degrees of antimicrobial-resistant Salmonella isolates recovered from localized areas in ESV is concerning. The discovery of such S. enterica isolates in small communities can impact the supply chain and future farm tracebacks with regards to the new FSMA regulations.