title: In vitro invasion efficiency and intracellular proliferation rate comprise virulence-related phenotypic traits of Neospora caninum.
abstract: In this study, we examined the in vitro invasion and proliferation capacities of the Nc-Liv and ten Spanish Neospora caninum isolates (Nc-Spain 1 H - Nc-Spain 10). The invasion rate was determined as the number of tachyzoites that completed their internalisation into MARC-145 cells at 2, 4, and 6 h post-inoculation (pi). The proliferation rate was evaluated by determining the doubling time during the exponential proliferation period. Significant differences in the invasion rates of these isolates were detected at 2 and 4 h pi (P < 0.0001, Kruskal-Wallis test). At 4 h pi, the Nc-Spain 4 H and Nc-Liv isolates displayed the highest, while the Nc-Spain 3 H and Nc-Spain 1 H isolates had the lowest invasion rates (by Dunn's test). Variations in the proliferation kinetics of these isolates were also observed. Between different isolates, the lag phase, which occurs before the exponential growth phase, ranged from 8 to 44 h, and the doubling time ranged from 9.8 to 14.1 h (P = 0.0016, ANOVA test). Tachyzoite yield, which combines invasion and proliferation data, was also assessed and confirmed marked differences between the highly and less prolific isolates. Interestingly, a direct correlation between the invasion rates and tachyzoite yields, and the severity of the disease that was exhibited by infected pregnant mice in previous works could be established for the isolates in this study (Spearman's coefficient > 0.62, P < 0.05). The results of this study may help us to explain the differences in the pathogenicity that are displayed by different isolates.
authors.affiliation: SALUVET, Animal Health Department, Complutense University of Madrid, Ciudad Universitaria s/n, 28040 Madrid, Spain. jregidor@vet.ucm.es.
authors.forename: Javier
authors.initials: J
authors.lastname: Regidor-Cerrillo
authors.forename: Mercedes
authors.initials: M
authors.lastname: Gómez-Bautista
authors.forename: Itsaso
authors.initials: I
authors.lastname: Sodupe
authors.forename: Gorka
authors.initials: G
authors.lastname: Aduriz
authors.forename: Gema
authors.initials: G
authors.lastname: Álvarez-García
authors.forename: Itziar
authors.initials: I
authors.lastname: Del Pozo
authors.forename: Luis Miguel
authors.initials: LM
authors.lastname: Ortega-Mora
mesh_terms: D000818:Animals; D002460:Cell Line; D003048:Coccidiosis / Q000469:parasitology*; D000882:Haplorhini; D008018:Life Cycle Stages; D018688:Neospora / Q000235:genetics / Q000254:growth & development / Q000472:pathogenicity* / Q000502:physiology*; D010641:Phenotype; D016133:Polymerase Chain Reaction / Q000662:veterinary; D014774:Virulence