Salmonella Indiana as a cause of abortion in ewes: Genetic diversity and resistance patterns

Salmonella enterica subspecies enterica Indiana, a food-borne serovar uncommon in most countries, was responsible for an outbreak of abortion in a flock of Lacaune dairy ewes in southern Spain. Drinking water and feedstuff samples were analysed in an attempt to determine the source of the infection. Pigeons (Columba livia) and turtledoves (Streptopelia turtur) in close contact with the ewes were captured and examined for the bacterium. Seventeen S. Indiana strains were isolated from the ewes and wild birds and the genetic similarity among them analysed by Pulsed Field Gel Electrophoresis (PFGE) after the digestion of their genomic DNA with the restriction enzyme XbaI. The results suggest the wild birds might be responsible for the outbreak in the ewes. The strains recovered were fully susceptible to 15 out of the 16 antimicrobial agents tested: ampicillin, amoxycillin clavulanate, cephalothin, ceftriaxone, gentamicin, neomycin, streptomycin, tetracycline, ciprofloxacin, enrofloxacin, sulphonamides, trimethoprim-sulphamethoxazole, apramycin, colistin and chloramphenicol. Differences in the resistance pattern to nalidixic acid were observed; 11 strains (64.7%) were nalidixic acid resistant (R-Nx) and 6 (35.3%) sensitive (S-Nx). Among the R-Nx strains, a substitution of Gly to Cys at position 81 (Gly81àCys) of the gyrA gene in 10 strains isolated from wild birds and ovine foetuses, and of Asp to Tyr at position 87 (Asp87àTyr) in one strain isolated from ewe faeces, were revealed by sequencing the gene. To control the outbreak, enrofloxacin treatment was administered for 5 days. The same therapy was used to prevent infection during following gestation cycles, administering the antimicrobial agent at presentation and over 4 weeks before birth. Anti-bird meshes and closed drinking and feeding troughs were also installed to prevent further contact of the ewes with wild birds.