Science Page: Salmonella antimicrobial resistance and emergence of a new serotype S.4,[5],12:i:-

This is our Friday rubric: every week a new Science Page from the Bob Morrison’s Swine Health Monitoring Project. The previous editions of the science page are available on our website.

Monitoring antimicrobial resistance is a research topic of utmost importance in the swine industry. Dr. Julio Alvarez at the University of Minnesota is leading some of this effort and this week, his team is presenting the latest results regarding Salmonella antimicrobial resistance in the strains isolated by the University of Minnesota – Veterinary Diagnostic Laboratory between the years 2006 and 2015 and the emergence of a new serotype S.4,[5],12:i:-

Key Points

  • Swine is the reservoir most commonly associated with the S.4,[5],12:i: serotype.
  • The prevalence of S. agona and S. 4,[5],12:i:- in isolates of swine origin recovered from clinical samples received at the Minnesota Veterinary Diagnostic Laboratory (MVDL) in 2006-2015 has increased.
  • In these serotypes an increased proportion of isolates were resistant to ceftiofur and enrofloxacin, compared with other serotypes.
  • The increase in the frequency of isolation of the S.4,[5],12:i:- serotype in humans may be paralleled by a similar increase in swine clinical samples received in the MVDL.

The information synthesized in the figure below is the evolution, over the years, of the percentages of Salmonella isolated at the UMN – VDL, belonging to each of other the following serotypes: typhimurium, agona, derby, typhymurium var5, and 4,5,12:i:-. The increase in the proportion of S.4,5,12:i:- can be seen starting back in 2011-2012.

Salmonella antibiotic resistance

Click here to read the full report about Salmonella serotypes isolated at the UMN – VDL

Beneficial but variable effect of vaccination to control Salmonella in pigs

In this meta-analysis conducted by the Center for Veterinary Health Surveillance (Madrid, Spain) in collaboration with Drs. Conrado, Perez, and Alvarez from the University of Minnesota, the efficacy of vaccination to control Salmonella infection in pigs was evaluated. The meta-analysis reviewed a total of 44 studies focusing on Salmonella typhimurium or Salmonella choleraesuis. Included protocols were using either inactivated (killed) or live-attenuated vaccines.

Results showed that both vaccine types had a similar efficacy and that the most successful control strategies among the ones reviewed were using killed vaccines to control Salmonella choleraesuis.

Alvarez swine salmonella vaccine 2017

Abstract: Consumption or handling of improperly processed or cooked pork is considered one of the top sources for foodborne salmonellosis, a common cause of intestinal disease worldwide. Asymptomatic carrier pigs may contaminate pork at slaughtering; therefore, pre-harvest reduction of Salmonella load can contribute to reduce public health risk. Multiple studies have evaluated the impact of vaccination on controlling Salmonella in swine farms, but results are highly variable due to the heterogeneity in vaccines and vaccination protocols. Here, we report the results of an inclusive systematic review and a meta-analysis of the peer-reviewed scientific literature to provide updated knowledge on the potential effectiveness of Salmonella vaccination. A total of 126 articles describing the use of Salmonella vaccines in swine were identified, of which 44 fulfilled the inclusion criteria. Most of the studies (36/44) used live vaccines, and S. Typhimurium and S. Choleraesuis were the predominant serotypes evaluated. Vaccine efficacy was most often measured through bacteriological isolation, and pooled estimates of vaccine efficacy were obtained as the difference in the percentage of positive animals when available. Attenuated and inactivated vaccines had similar efficacy [Risk Difference = − 26.8% (− 33.8, − 19.71) and − 29.5% (− 44.4, − 14.5), respectively]. No serotype effect was observed on the efficacy recorded for attenuated vaccines; however, a higher efficacy of inactivated vaccines against S. Choleraesuis was observed, though in a reduced sample.

Results from the meta-analysis here demonstrate the impact that vaccination may have on the control of Salmonella in swine farms and could help in the design of programs to minimize the risk of transmission of certain serotypes through the food chain.

Link to the full article

Monitoring Salmonella resistance to antimicrobials in Minnesota during the past 9 years

The STEMMA laboratory at the University of Minnesota and more particularly Dr. Alvarez’s team is aiming at monitoring of antimicrobial resistance in animal and human bacteria. Therefore, the research they present in this article published this month, focused on Salmonella species both in swine and cattle. Records from the Veterinary Diagnostic Laboratory between 2006 and 2015 were compiled to study the evolution of the proportion of resistant strains of Salmonella in Minnesota.

Dr Hong, in collaboration with researchers from the U of MN, captured the number and the type of antimicrobials each strain was resistant to. He also monitored the evolution of the resistances over the nine-year period.

Evolution in antimicrobial resistant Salmonella isolates
recovered from swine at the MVDL in 2006–2015.

Explanation of the figure: Proportion of Salmonella isolates recovered from swine samples that were resistant to ampicillin (A), ceftiofur (C), enrofloxacin (E), florfenicol (F), gentamicin (G), neomycin (N), oxytetracycline (O), sulfadimethoxine (Sul), spectomycin (Sp) and trimethorpim/ sulfamethoxazole (Ts)

Abstract: Salmonellosis remains one of the leading causes of foodborne disease worldwide despite preventive efforts at various stages of the food production chain. The emergence of multi-drug resistant (MDR) non-typhoidal Salmonella enterica represents an additional challenge for public health authorities. Food animals are considered a major reservoir and potential source of foodborne salmonellosis; thus, monitoring of Salmonella strains in livestock may help to detect emergence of new serotypes/MDR phenotypes and to gain a better understanding of Salmonella epidemiology. For this reason, we analyzed trends over a nine-year period in serotypes, and antimicrobial resistance, of Salmonella isolates recovered at the Minnesota Veterinary Diagnostic Laboratory (MVDL) from swine (n = 2,537) and cattle (n = 1,028) samples. Prevalence of predominant serotypes changed over time; in swine, S. Typhimurium and S. Derby decreased and S. Agona and S. 4,5,12:i:- increased throughout the study period. In cattle, S. Dublin, S. Montevideo and S. Cerro increased and S. Muenster became less frequent. Median minimum inhibitory concentration (MIC) values and proportion of antibiotic resistant isolates were higher for those recovered from swine compared with cattle, and were particularly high for certain antibiotic-serotype combinations. The proportion of resistant swine isolates was also higher than observed in the NARMS data, probably due to the different cohort of animals represented in each dataset. Results provide insight into the dynamics of antimicrobial resistant Salmonella in livestock in Minnesota, and can help to monitor emerging trends in antimicrobial resistance.

Link to the full article