Inter- and intra-strain variation and PCR detection of the internal transcribed spacer 1 (ITS-1) sequences of Australian isolates of Eimeria species from chickens

Abstract

The objective of this study was to confirm the presence of seven species of Eimeria involved in chicken coccidiosis in Australia by comparing internal transcribed spacer 1 (ITS-1) sequences, ITS-1 polymerase chain reaction (PCR) methods and to apply phylogenetic analysis to assess evolutionary relationships of Australian isolates. Twenty-two distinct ITS-1 regions of 15 Australian Eimeria isolates were sequenced, and analysed using maximum parsimony, distance and maximum likelihood methods. Poor bootstrap support, resulting from high ITS-1 sequence heterogeneity between all species groups, resulted in polychotomy of the Eimeria species in all three trees generated by these analyses. Percentage identity analyses revealed two distant ITS-1 lineages in both E. mitis and E. maxima at the same levels that separate the two species E. tenella and E. necatrix. One E. maxima lineage consisted of Australian isolates, the other American isolates, with one European sequence (originating from the same isolate) in each lineage. One Australian E. praecox sequence was only distantly related (33% variation) to three E. praecox sequences from Australian and European isolates. Short and long ITS-1 variants were isolated from both E. tenella (cloned line) and E. necatrix isolates with deletions (106 and 73 bp, respectively) in the short variants within the 3' region of the ITS-1 sequence. ITS-1 sequences of strains of both E. brunetti and E. acervulina species varied the least. Apart from E. maxima, all of the ITS-1 sequences of the six remaining individual species clustered to the exclusion of other species in all phylogenetic trees. Published ITS-1 tests for E. necatrix, E. acervulina, E. brunetti and E. tenella, combined with three new tests for E. mitis, E. praecox and Australian E. maxima amplified all respective Australian isolates specifically in a nested format using conserved ITS-1 PCR products as template to improve the sensitivity. All PCR tests were confirmed against a collection of 24 Australian chicken Eimeria isolates and contaminating species were detected in some instances. In conclusion, once the genetic variation between species and strains is determined, the ITS-1 is a good target for the development of species-specific assays, but the ITS-1 sequences alone do not seem suitable for the confirmation of phylogenetic inferences for these species. This study reports the first attempt at the analysis of the phylogeny and sequence comparison of the Eimeria species involved in chicken coccidiosis in Australia.