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ARS Home » Northeast Area » Beltsville, Maryland (BARC) » Beltsville Agricultural Research Center » Environmental Microbial & Food Safety Laboratory » Research » Publications at this Location » Publication #349906
Research Project: Antimicrobial Resistance and Ecology of Zoonotic Foodborne Pathogens in Dairy Cattle

Location: Environmental Microbial & Food Safety Laboratory

Title: Rivers on the Maryland Eastern Shore are a reservoir for antibiotic-resistant Salmonella enterica

Author
item CALLAHAN, MARY THERESA - University Of Maryland
item SHEPARD, SUSAN - University Of Maryland
item Van Kessel, Jo Ann
item MICALLEF, SHIRLEY - University Of Maryland

Submitted to: International Association for Food Protection
Publication Type: Abstract Only
Publication Acceptance Date: 1/16/2018
Publication Date: 7/9/2018
Citation: Callahan, M., Shepard, S., Van Kessel, J.S., Micallef, S.A. 2018. Rivers on the Maryland Eastern Shore are a reservoir for antibiotic-resistant Salmonella enterica. International Association for Food Protection. p. 1.

Interpretive Summary:

Technical Abstract: Introduction: Some outbreaks of salmonellosis associated with produce have been traced back to farms on the Delmarva Peninsula, a few specifically to irrigation water, suggesting an environmental reservoir for Salmonella enterica in this region. A high diversity of S. enterica in Delmarva surface water used for irrigation has been reported, but further research on S. enterica ecology in this region is needed. Purpose: Evaluate antimicrobial resistance (AMR) among S. enterica isolates collected from rivers on the Maryland Eastern Shore. Methods: A total of 157 Salmonella isolates were recovered from 23 sites along the Choptank, Nanticoke, Pocomoke, and Wicomico Rivers in the fall and the spring using modified Moore Swabs. Swabs were selectively enriched for the presence of S. enterica. Presumptive salmonellae were serotyped and antimicrobial susceptibility testing was performed with the Sensititre microbroth dilution system using the National Antimicrobial Resistance Monitoring System (NARMS) custom plate CMV1AGNF. Resistance breakpoints were obtained from the Clinical and Laboratory Standards Institute. Results: Salmonella diversity was high and a total of 18 serotypes were recovered. Twenty five isolates (16%) from 9 water samples were resistant to at least one class of antibiotics. Only one S. Typhimurium isolate from the fall sampling showed AMR. Of the 25 isolates, 52% (13) were multidrug resistant (MDR, resistant to at least two classes of antibiotics), including 9 isolates that were resistant to five classes of antibiotics. S. Typhimurium was the serotype most commonly found to be antibiotic resistant. Resistance to sulfisoxazole was the most prevalent, followed by tetracycline. AMR to amoxicillin/clavulanic acid, ampicillin, cefoxitin, ceftriaxone and streptomycin was also elevated. Significance: The prevalence of MDR Salmonella on the Maryland Eastern Shore is a significant public health concern, as the majority of farms in this region use surface water for at least some of their irrigation needs.