Diversity, distribution and antibiotic resistance of Enterococcus spp. recovered from tomatoes, leaves, water and soil on U.S. Mid-Atlantic farms

• Published in: Food microbiology 2013-12, Vol.36 (2), p.465-474
• Main Authors: Micallef, Shirley A., Rosenberg Goldstein, Rachel E., George, Ashish, Ewing, Laura, Tall, Ben D., Boyer, Marc S., Joseph, Sam W., Sapkota, Amy R.
• Format: Article
• Language: English
• Subjects: Amplified fragment length polymorphism; Anti-Bacterial Agents - pharmacology; Antibiotic resistance; Biodiversity; Biological and medical sciences; ciprofloxacin; Enterococcus; Enterococcus - classification; Enterococcus - drug effects; Enterococcus - genetics; Enterococcus - isolation & purification; Enterococcus casseliflavus; Enterococcus faecalis; Enterococcus faecium; Enterococcus gallinarum; Enterococcus hirae; Enterococcus raffinosus; Enterococcus spp; farm to fork; farms; Food industries; Food microbiology; Food safety; Fruit - microbiology; Fundamental and applied biological sciences. Psychology; General aspects; groundwater; Groundwater - microbiology; habitats; Hygiene and safety; irrigation; leaves; Lycopersicon esculentum; Lycopersicon esculentum - microbiology; Microbial Sensitivity Tests; Mid-Atlantic Region; pathogens; Plant Leaves - microbiology; Pre-harvest tomatoes; rifampicin; risk; Soil; Soil Microbiology; tomatoes; Water
• ISSN: 0740-0020; 1095-9998
• DOI: 10.1016/j.fm.2013.04.016

Antibiotic-resistant enterococci are important opportunistic pathogens and have been recovered from retail tomatoes. However, it is unclear where and how tomatoes are contaminated along the farm-to-fork continuum. Specifically, the degree of pre-harvest contamination with enterococci is unknown. We evaluated the prevalence, diversity and antimicrobial susceptibilities of enterococci collected from tomato farms in the Mid-Atlantic United States. Tomatoes, leaves, groundwater, pond water, irrigation ditch water, and soil were sampled and tested for enterococci using standard methods. Antimicrobial susceptibility testing was performed using the Sensititre microbroth dilution system. Enterococcus faecalis isolates were characterized using amplified fragment length polymorphism to assess dispersal potential. Enterococci (n = 307) occurred in all habitats and colonization of tomatoes was common. Seven species were identified: Enterococcus casseliflavus, E. faecalis, Enterococcus gallinarum, Enterococcus faecium, Enterococcus avis, Enterococcus hirae and Enterococcus raffinosus. E. casseliflavus predominated in soil and on tomatoes and leaves, and E. faecalis predominated in pond water. On plants, distance from the ground influenced presence of enterococci. E. faecalis from samples within a farm were more closely related than those from samples between farms. Resistance to rifampicin, quinupristin/dalfopristin, ciprofloxacin and levofloxacin was prevalent. Consumption of raw tomatoes as a potential exposure risk for antibiotic-resistant Enterococcus spp. deserves further attention. •Enterococci were ubiquitous on tomato farms.•Pre-harvest tomatoes were frequently contaminated.•Enterococci were more likely to be present on fruit and leaves close to the ground.•Enterococcus faecalis dispersed efficiently between habitats within the tomato farm setting.•Rifampicin, quinupristin/dalfopristin and fluoroquinolone resistance was prevalent.