Abstract
In 2010, Romaine lettuce grown in southern Arizona was implicated in a multi-state outbreak of Escherichia coli O145:H28 infections. This was the first known Shiga toxin-producing E. coli (STEC) outbreak traced to the southwest desert leafy green vegetable production region along the United States-Mexico border. Limited information exists on sources of STEC and other enteric zoonotic pathogens in domestic and wild animals in this region. According to local vegetable growers, unleashed or stray domestic dogs and free-roaming coyotes are a significant problem due to intrusions into their crop fields. During the 2010–2011 leafy greens growing season, we conducted a prevalence survey of STEC and Salmonella presence in stray dog and coyote feces. Fresh fecal samples from impounded dogs and coyotes from lands near produce fields were collected and cultured using extended enrichment and serogroup-specific immunomagnetic separation (IMS) followed by serotyping, pulsed-field gel electrophoresis (PFGE), and antimicrobial susceptibility testing. A total of 461 fecal samples were analyzed including 358 domestic dog and 103 coyote fecals. STEC was not detected, but atypical enteropathogenic E. coli (aEPEC) strains comprising 14 different serotypes were isolated from 13 (3.6%) dog and 5 (4.9%) coyote samples. Salmonella was cultured from 33 (9.2%) dog and 33 (32%) coyote samples comprising 29 serovars with 58% from dogs belonging to Senftenberg or Typhimurium. PFGE analysis revealed 17 aEPEC and 27 Salmonella distinct pulsotypes. Four (22.2%) of 18 aEPEC and 4 (6.1%) of 66 Salmonella isolates were resistant to two or more antibiotic classes. Our findings suggest that stray dogs and coyotes in the desert southwest may not be significant sources of STEC, but are potential reservoirs of other pathogenic E. coli and Salmonella. These results underscore the importance of good agriculture practices relating to mitigation of microbial risks from animal fecal deposits in the produce production area.
Highlights
Foodborne disease illnesses caused by pathogen contamination of fresh produce are being recognized in greater numbers in the United States (U.S.) and abroad [1], [2]
Shiga toxin-producing E. coli was not detected in any fecal samples, but atypical enteropathogenic E. coli (aEPEC) strains were isolated from 13 (3.6%) dog and 5 (4.9%) coyote fecal samples
In November 2010, a higher seasonal prevalence of Salmonella was observed at the California and Mexico shelters, primarily due to a specific serovar (Senftenberg) as described below
Summary
Foodborne disease illnesses caused by pathogen contamination of fresh produce are being recognized in greater numbers in the United States (U.S.) and abroad [1], [2]. While norovirus infections transmitted downstream during post-harvest handling are likely the major driver of these statistics, reports of fresh produce-associated outbreaks from zoonotic agents potentially spread by domestic and wild animal reservoirs in the pre-harvest environment are clearly contributing to this disease burden [6], [7]. The role of domestic animals and wildlife as potential sources and transmitters of zoonotic bacterial pathogens to lettuce and other leafy greens and agriculture water has been studied at length in the central California coast [9], [10], [11], [12], [13]. In addition to concerns about human sources of foodborne pathogens near leafy green production areas of the desert, growers report problems with unleashed, free-roaming domestic dogs (Canis familiaris) entering their fields. Growers report frequent coyote (Canis latrans) sightings and signs (tracks, scat, feces) on roads adjacent to produce fields where tractors and other equipment are used
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