Buffered peptone water promotes the transfer of antimicrobial resistance genes to Salmonella in swine cecal samples

Authors: Anderson, Christopher

Submitted to: Conference Research Workers Disease Meeting
Publication Type: Abstract Only
Publication Acceptance Date: 1/22/2023
Publication Date: N/A
Citation: N/A

Interpretive Summary:

Technical Abstract: Buffered peptone water (BPW) is often used as a non-selective pre-enrichment media for the resuscitation of Salmonella prior to selective enrichment and isolation. However, BPW enriches bacterial populations that readily transfer genetic elements to Salmonella, and the potential for antimicrobial resistance transfer during pre-enrichment needs to be better appreciated. Here, the objective was to evaluate the transfer of antimicrobial resistance to Salmonella in swine cecal samples incubated in BPW. Swine cecal samples were spiked with nalidixic acid resistant and ampicillin sensitive Salmonella enterica serovar Typhimurium x4232 (104 CFU per gram) and incubated in BPW, Gram-negative broth, or tetrathionate broth for 24 hours. '4232 was differentially recovered, and the percentage of cells resistant to ampicillin was enumerated. In addition, the diversity of plasmids in Salmonella isolates resistant to ampicillin and the microbial profiles after enrichment were evaluated. The proportion of Salmonella resistant to ampicillin was significantly higher in cecal samples incubated in BPW and Gram-negative broth compared to tetrathionate broth. Upwards of 40% of recovered Salmonella were resistant to ampicillin in some cecal samples incubated in BPW. Plasmid sequencing of the isolates resistant to ampicillin demonstrated the transfer of multiple plasmid types that encoded known resistance genes. Further, sequencing of the bacterial communities of the enrichments confirmed that BPW increased the relative abundance of bacteria that are known to transfer plasmids to Salmonella. These findings demonstrate that BPW can promote the transfer of plasmids when the bacterial donor populations are present with compatible plasmid types. Given that BPW is commonly used as a pre-enrichment media, our findings suggest that the antimicrobial resistance profiles of some recovered isolates could be due to the acquisition of plasmids during pre-enrichment. The results of this study should be confirmed with more diverse sample types and Salmonella strains.