Abstract
Nontyphoidal Salmonella infections contribute to approximately 1.2 million annual illnesses in the United States. Historical and recent outbreaks have been associated with dairy products, ground beef, and direct contact with cattle. Salmonella antimicrobial resistance (AMR) is a serious concern that can reduce successful treatment of infections, increasing recovery time, medical costs, and mortality rates in humans and animals. This highlights the need to track AMR in Salmonella isolated from cattle to improve treatment plans, manage trends in AMR, and prevent future AMR development. A total of 242 Salmonella isolates were retrieved from 9,162 cattle fecal samples submitted to the University of California, Davis Veterinary Medical Teaching Hospital from 2002 to 2016. These isolates were tested for antimicrobial susceptibility using a standardized broth dilution panel. Multidrug resistance (MDR) to three or more classes of antimicrobials was observed in 50.8% of isolates, and the most common MDR pattern was amoxicillin-ampicillin-cefoxitin-ceftiofur-ceftriaxone-chloramphenicol-streptomycin-tetracycline (23.2%). There were significantly greater odds for antimicrobial resistance to aminoglycosides (OR: 2.03, 95% CI: 1.1–3.7), penicillins (OR: 1.87, 95% CI: 1.007–3.5), and tetracyclines (OR: 1.87, 95% CI: 1.017–3.4) for the 2002–2009 period when compared to the 2010–2016 period. The most prevalent MDR serotypes were Newport (100% MDR, n = 52), Typhimurium (100%, n = 20), and Dublin (71% MDR, n = 46). Risk factors associated with higher odds for isolating MDR Salmonella included isolates from calves when compared to adult cattle (OR: 22.0; 95% C.I.: 3.9–125.7), and isolates obtained from cattle suspect of having salmonellosis versus from the infectious disease control surveillance program (OR:13.7; 95%C.I.: 2.8–66.8). Despite a temporal trend for reduced AMR to most antimicrobial drug classes, a lack of this observed in the 2002–2009 period when compared to the 2010–2016 period for important drug classes such as cephalosporins (OR: 1.6, 95% CI: 0.87–3.1), and a trend for temporal increase in resistant to quinolones drugs (P value 0.004) highlight the relevance of AMR surveillance in cattle with Salmonella infections with the aim of targeting future prophylactic interventions.
Highlights
Nontyphoidal Salmonella is categorized by the Centers for Disease Control and Prevention (CDC) as one of the top eighteen drug-resistant threats in the United States, associated with an estimated 1.2 million infections, 100,000 antimicrobial-resistant infections, and 300 million dollars in medical costs annually [1]
To better understand spread and dissemination of antimicrobial resistance, this study aims to describe antimicrobial resistance trends in Salmonella isolated from dairy cattle in northern California
Some of the isolates were recovered from dairy cattle exhibiting clinical signs of salmonellosis, and the remaining isolates were recovered through the Veterinary Medical Teaching Hospital (VMTH) Infectious Disease Control (IDC) program from asymptomatic dairy cattle
Summary
Nontyphoidal Salmonella is categorized by the Centers for Disease Control and Prevention (CDC) as one of the top eighteen drug-resistant threats in the United States, associated with an estimated 1.2 million infections, 100,000 antimicrobial-resistant infections, and 300 million dollars in medical costs annually [1]. Dairy cattle and dairy products have been demonstrated to be potential reservoirs for nontyphoidal Salmonella including serotypes known to display AMR and cause foodborne illness in humans, such as Salmonella serotypes Newport and Typhimurium [4]. Recent Salmonella outbreaks and observed resistance to medically-important drugs such as cephalosporins [6], highlight the continuing need for spatiotemporal quantification of AMR in non-typhoidal Salmonella in dairy cattle. This will facilitate estimating areas with higher risk for outbreaks caused by drug-resistant strains, facilitating prevention and management to reduce the spread and dissemination of AMR Salmonella
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