Purpose: This study examined the prevalence and antibiotic susceptibilities of Escherichia coli and Enterococcus spp. in soil and vegetables associated with urban agriculture.
Methods: Fifteen soil and 48 vegetable samples were collected from three urban gardens in Detroit. Escherichia coli and Enterococcus spp. were isolated and identified by PCR. Unique isolates were identified as Enterococcus spp. by PCR and 16S rRNA sequencing. The disc diffusion test was used to examine the antimicrobial susceptibility profile of all unique isolates of E. coli and Enterococcus spp. Pulsed-field gel electrophoresis (PFGE) was performed to distinguish the bacteria at the molecular level.
Results: Out of 15 soil samples, 9 (60%) carried E. coli and 14 (93%) contained Enterococcus spp. Of 48 vegetable samples, 23 (48%) were positive for E. coli and 38 (79%) for Enterococcus spp. Enterococcus mundtii (47%) was the most abundant Enterococcus spp. in soil, followed by Enterococcus durans (20%) and Enterococcus casseliflavus (13%). In contrast, the vast majority of Enterococcus spp. from vegetables was identified as Enterococcus faecalis (82%). Eschericha coli showed resistance to ampicillin, only, in 33% of soil and 61% of vegetable samples. Streptomycin resistance was observed in 64% of Enterococcus spp. from soil, followed by 7% to ciprofloxacin. Streptomycin resistance was the most prominent in Enterococcus spp. in vegetables (79%). Further, resistance to ampicillin (32%), ciprofloxacin (8%), erythromycin (8%), and tetracycline (8%) was observed in Enterococcus spp. of vegetable origin. PFGE results demonstrated a diverse population of E. coli, but no unique patterns identified in isolates from soil or vegetables.
Significance: Common foodborne bacteria are prevalent in the urban agricultural system and may serve as a vital source of food contamination and antibiotic resistance.