Whole-genome sequencing of Salmonella serovars isolated from diarrheic and non-diarrheic foals.

Whole-genome sequencing was used to analyze Salmonella isolates from diarrheic and non-diarrheic foals, focusing on their resistance, virulence, and stress response genes, revealing a notable presence of multidrug resistance especially in isolates from diarrheic foals.

Background and Objective

• Pathogen Focus: Salmonella spp. are recognized as significant pathogens in foals, often responsible for clinical enterocolitis (inflammation of the intestine) and sepsis (systemic infection).
• Research Goal: To characterize the genetic determinants associated with antibiotic resistance, virulence factors, and stress response in Salmonella isolates from foals with or without diarrhea.
• Sampling: The study involved 23 Salmonella isolates taken from fecal samples of 16 diarrheic foals and 7 non-diarrheic foals, all under one year of age.

Methods

• Whole-genome sequencing (WGS): This technique was applied to all isolates to obtain comprehensive genetic data.
• Analysis Targets: Resistance genes (antimicrobial resistance genes, ARGs), virulence genes, and stress response genes were specifically analyzed from the genome data.

Results

• Serovars Detected: The most common Salmonella serovars in diarrheic foals belonged to subspecies enterica, particularly serovars Infantis and Minnesota.
• Multidrug Resistance: 9 out of 23 isolates showed multidrug resistance (MDR), with 8 of these 9 isolates coming from foals exhibiting diarrhea.
• Resistance Gene Inventory:
  • All isolates had at least 2 resistance genes.
  • Most resistance genes were associated with multidrug efflux pump complexes, which help bacteria expel antibiotics and survive treatment.
• β-Lactam Resistance:
  • 9 isolates showed resistance to β-lactam antibiotics.
  • These isolates carried at least one ARG responsible for β-lactam antibiotic inactivation (such as genes encoding beta-lactamase enzymes).
• Quinolone Resistance:
  • 7 isolates were resistant to quinolones, an important class of broad-spectrum antibiotics.
  • 3 of these contained quinolone resistance genes.

Discussion and Implications

• Higher MDR in Diarrheic Foals: The finding that most multidrug-resistant isolates come from foals with diarrhea suggests that infection severity might correlate with resistance potential or that antibiotic treatment in these animals selects for resistant strains.
• Zoonotic Potential: Salmonella species have the ability to infect humans and other animals, so resistant Salmonella strains in foals represent a public health concern.
• Recommendations: The study highlights the need for strict biosecurity measures on farms to control the spread of multidrug-resistant Salmonella, including hygiene protocols, quarantine measures, and prudent use of antibiotics.

Conclusion

• This research underscores the presence of antimicrobial resistance in Salmonella isolates from foals, particularly those with diarrhea.
• Whole-genome sequencing provides a comprehensive approach to understanding pathogen genetics relevant to disease and resistance patterns.
• Farm management strategies must consider these findings to prevent spread of MDR Salmonella and reduce zoonotic risks to animal handlers and the public.