OBJECTIVETo type the Chinese Anaplasma phagocytophilum isolates by Multispacer typing (MST).

METHODSBased on the genomes of the 4 published Anaplasma strains, 4 genomic sequences were analyzed by Mauve 2.3.1 software and variable spacer sequences were selected for designing primers with the bio-software Primer Premier 5.0. A total of 11 Chinese A. phagocytophilum isolates, obtained from different areas of China during 2009-2012 were assayed by the MST. Twenty two intergenic sequences for each isolate tested and the reference A. phagocytophilum strain Webster and A. phagocytophilum strain HZ were concatenated in the order of HGA-mst 1F/1R-mst 2F/2R, HGA-mst 22F/22R.

RESULTSTwenty two pairs of primers were successfully used for typing the Human granulocytic anaplasmosis (HGA) strains in the study. Those 22 intergenic sequences exhibited a great diversity among the strains tested and each of the strain tested was identified as unique genotype, according to the alignment analysis of the 22 concatenated intergenic sequences. Of these single nucleotide polymorphism (SNPs) identified in the study, the nucleotide transitions shared the highest percentage (60.2%, 251/417) and then the nucleotide transversion, accounted for 23.0% (96/417) and the indel events (insertion/deletion) were observed of 16.7% (70/417)SNPs. Phylogenetic analysis indicated that the 5 strains from patients (LZ-H1, LZ-H2, LZ-H3, LZ-H4, LZ-H5) from Laizhou areas, Shandong province and 1 tick strain (LZ-T1) from Haemaphysalis longicornis collected from the same areas where the patients lived were grouped in the same clan with the reference A. phagocytophilum strain Webster and strain HZ. Beijing isolates (BJ-H1) grouped with Xinjiang isolates (XJ-H1 and XJ-H3) while another tick isolates from Laizhou areas (LZ-T2) and another Xinjiang human isolate(XJ-H2)were in the same clan, which was closely related to the isolates from severe patients in Laizhou.

CONCLUSIONChinese HGA isolates exhibited a great diversity of intergenic regions. MST seemed a valuable tool for the detection and tracing for any endemic strains of Anaplasma during the outbreak investigations in the public health events.