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. 2023 Nov 25;12(12):1662.
doi: 10.3390/antibiotics12121662.

Serovars, Virulence and Antimicrobial Resistance Genes of Non-Typhoidal Salmonella Strains from Dairy Systems in Mexico

Stephany Barrera  1 , Sonia Vázquez-Flores  1 , David Needle  2 , Nadia Rodríguez-Medina  3 , Dianella Iglesias  1 , Joseph L Sevigny  4 , Lawrence M Gordon  4 , Stephen Simpson  4 , W Kelley Thomas  4 , Hectorina Rodulfo  1 , Marcos De Donato  1   5
Affiliations

Serovars, Virulence and Antimicrobial Resistance Genes of Non-Typhoidal Salmonella Strains from Dairy Systems in Mexico

Stephany Barrera et al. Antibiotics (Basel). .

Abstract

Salmonella isolated from dairy farms has a significant effect on animal health and productivity. Different serogroups of Salmonella affect both human and bovine cattle causing illness in both reservoirs. Dairy cows and calves can be silent Salmonella shedders, increasing the possibility of dispensing Salmonella within the farm. The aim of this study was to determine the genomic characteristics of Salmonella isolates from dairy farms and to detect the presence of virulence and antimicrobial resistance genes. A total of 377 samples were collected in a cross-sectional study from calves, periparturient cow feces, and maternity beds in 55 dairy farms from the states of Aguascalientes, Baja California, Chihuahua, Coahuila, Durango, Mexico, Guanajuato, Hidalgo, Jalisco, Queretaro, San Luis Potosi, Tlaxcala, and Zacatecas. Twenty Salmonella isolates were selected as representative strains for whole genome sequencing. The serological classification of the strains was able to assign groups to only 12 isolates, but with only 5 of those being consistent with the genomic serotyping. The most prevalent serovar was Salmonella Montevideo followed by Salmonella Meleagridis. All isolates presented the chromosomal aac(6')-Iaa gene that confers resistance to aminoglycosides. The antibiotic resistance genes qnrB19, qnrA1, sul2, aph(6)-Id, aph(3)-ld, dfrA1, tetA, tetC, flor2, sul1_15, mph(A), aadA2, blaCARB, and qacE were identified. Ten pathogenicity islands were identified, and the most prevalent plasmid was Col(pHAD28). The main source of Salmonella enterica is the maternity areas, where periparturient shedders are contaminants and perpetuate the pathogen within the dairy in manure, sand, and concrete surfaces. This study demonstrated the necessity of implementing One Health control actions to diminish the prevalence of antimicrobial resistant and virulent pathogens including Salmonella.

Keywords: Salmonella; antimicrobial resistance genes; calves; dairy farms; maternity beds; periparturient cows; virulence genes.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Venn diagram of Salmonella isolates for the identification of antimicrobial resistance determinants to the four most prevalent serovars. AMR = antimicrobial resistance.
Figure 2
Figure 2
Phylogenetic diversity of Salmonella isolates. The maximum-likelihood tree based on core genome SNPs was linked to a binary matrix, which represents the presence and absence of antimicrobial resistance (AMR) and virulence genes. Serovar, sample type, and location for each isolate were also included. Abbreviations; D, Durango; A, Aguascalientes; C, Coahuila; SLP, San Luis Potosí; T, Tlaxcala; BC, Baja California; USA, United States of America.
Figure 3
Figure 3
Venn diagram of Salmonella isolates for the identification of virulence genes by serovars.
Figure 4
Figure 4
States participating in Salmonella study (shown in gray). The farms where the sequenced isolates were obtained are shown in the map in red circles.
See this image and copyright information in PMC

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Grants and funding

This project was partially funded by Zoetis Mexico. CONACYT Mexico provided financial support to Stephany Barreras during her PhD program (704056).