Outbreaks of antimicrobial resistant Salmonella Choleraesuis in wild boars piglets from central-western Spain

Abstract

Salmonella enterica serovar Choleraesuis is the aetiological agent of swine paratyphoid being a highly invasive zoonotic pathogen. Wild boar natural populations are experiencing a demographical expansion as well as some farms are breeding this species to release for hunting with management sometimes identical to that of domestic pigs, including supplementation, grouping, and antibiotic treatments. This situation increases the chance of contact between wild boars and livestock, and potentially induces stress, with different sanitary consequences. The present work aims to describe the clinical features of recent outbreaks caused by S. Choleraesuis in wild boar from central-western Spain, as well as the antimicrobial resistance and phylogenetic relationships of isolates involved. 28 strains of S. Choleraesuis were isolated from 28 different wild boars belonging to 10 different game states located in central western Spain and submitted to the Clinical Veterinary Hospital (CVH) of the University of Extremadura. Samples were taken from different organs and cultured according to the ISO 6579:2002 procedure. Suspicious colonies were identified by PCR and antimicrobial resistance was evaluated by disc diffusion susceptibility test and the presence of the main resistance genes as well as 18 plasmid replicons frequently found among the Enterobacteriaceae was verified by PCR. Pulsed field gel electrophoresis was applied to determine the genetic relationship between isolates. The outbreaks under study were characterized by high mortality (35%-84%) and a septicaemic presentation. S. Choleraesuis was isolated from all the wild boars analysed, and 26 of the 28 isolates presented resistance to at least one antibiotic. The predominant resistances found were against sulphonamide, streptomycin, tetracycline, and doxicicline and sul1, strA-strB, and tetA were the most prevalent resistance genes among isolates. 10 strains carried FIIA, FIB+H/1 or FIIA+H/1 plasmids. PFGE classified the isolates into four different profiles, grouped into two clusters. This results show that prevention against S. Choleraesuis must be considered in the sanitary programs of the wild boar breeders.

Keywords: Salmonella Choleraesuis; antibiotic resistance; epidemiology; wild boar.

Figure 1

Location of the game estates. Political map of the Iberian Peninsula displaying the location of the different estates investigated in this study. (Inset: Location of the Iberian Peninsula in southwestern Europe)

Figure 2

Clinical symptoms and pathological findings. (a) Wild boar piglet with poor corporal condition. (b) Intense congestion observed in the abdominal cavity from a wild boar piglet. (c) Congestive lung displaying multiple pneumonic lesions. (d) Liver showing hepatomegaly and congestion. Inset: Magnification of the border of the right medial hepatic lobe displaying white spots in the parenchima. (e) Longitudinally opened jejunum section revealing a thickened mucosa and a dark and gritty content. (f) Colonic mucosa with multiple ulcers. Inset: Magnification of one of the colonic ulcers [Colour figure can be viewed at http://wileyonlinelibrary.com]

Figure 3

Phylogenetic relationship among 28 isolates of Salmonella enterica serotype Choleraesuis obtained from wild boars from the south‐central part of the Iberian Peninsula, listed with additional information about the date and place of the isolate as well as its genotypic and phenotypic resistance profile, plasmid presence and serological analysis to the presence of PCV‐2 and PRRSV. Dendogram shows four different profiles (SC1‐SC4) further clustered in groups A and B. Phenotipical resistance pattern: Su (sulphonamide); S (streptomycin); Te (tetracycline); Do (doxicycline); Na (nalidixic acid); N (neomycin); Sxt (trimethoprim/sulfamethoxazole); Am (ampicillin). Serological analisys: Neg (Negative); ‐ (Not tested). (Blanks represent absence of resistance or plasmids)