The species/biovars, region distribution, isolated years, and host profile of B. abortus
A total of seven biovars were observed in this population, including B. abortus bv. 1 (n = 24), B. abortus bv. 2 (n = 2), B. abortus bv. 3 (n = 60), B. abortus bv. 5 (n = 1), B. abortus bv. 6 (n = 2), B. abortus bv. 7 (n = 1), and B. abortus bv. 9 (n = 10). B. abortus bv. 3 was the dominant species in China (Table 1). These strains were collected from 14 provinces (cities and autonomous regions) from 1953 to 2013, including 36 strains in Inner Mongolia, 14 in Xinjiang, 11 in Hebei, 10 in Heilongjiang, 6 in Gansu, and 5 in Zhejiang; the remaining regions contained 1 to 4 strains, 85% strains was distributed in Northern, China. A total of 100 B. abortus samples were collected from 1953 to 2013, 11 in the 1950s, 9 in the 1960s, 5 in the 1970s, 38 in the 1980s, 1 in 1990, 4 in 2000s, and 32 in 2010s. Moreover, 100 strains were obtained from five hosts, 65 in cattle, 65%, followed by 20 in humans, 7 in sheep, 4 in yak, 3 in goat, and 1 in an unknown host (Table 1).
Table 1
Location, numbers, percentages (%), species, panel1, MLVA-11, hosts, and year of 100 Brucella abortus in this study.
Provinces | No. | Species-biovar | Panel1 | MLVA-11 | Host | Year |
Anhui | 1 | B. abortus bv. 2 | 28 | 82 | Cattle | 1955 |
Liaoning | 1 | B. abortus bv. 3 | 36 | 72 | Cattle | 1990 |
Beijing | 2 | B. abortus bv. 1, 3 | 28, 36 | 82,72 | Cattle | 1953, 1959 |
Ningxia | 2 | B. abortus bv. 3 | Ba8-3 | Ba11-1, 2 | Human, cattle | 1973, 1979 |
Shanghai | 2 | B. abortus bv. 1 | 28, 37 | 181, 77 | Cattle | 1954, 1964 |
Tianjin | 2 | B. abortus bv. 1 | 28, 37 | 82, 77 | Human | 1957 |
Chongqing | 4 | B. abortus bv. 3 | 36, 117 | 72, 328 | Human | 2011 |
Sichuan | 4 | B. abortus bv. 1, 2 | 28, 37 | 83, 77, 82 | Yak, Human | 1963, 1981 |
Zhejiang | 5 | B. abortus bv. 3, 7 | 36, 112 | 72, 326 | Human | 2006, 2008, 2013 |
Gansu | 6 | B. abortus bv. 9 | 112, 117 | 210, 327 | Cattle, sheep, Yaks, Goat | 1980 |
Heilongjiang | 10 | B. abortus bv. 3, 5, 6 | 36, Ba8-2 | 72, Ba11-4 | Cattle | 2010, 2012 |
Hebei | 11 | B. abortus bv. 3 | 36, 117, Ba8-1 | 72, 328, Ba11-3 | Cattle | 2011 |
Xinjiang | 14 | B. abortus bv. 1, 3, 9 | 28, 36, 112, 117 | 72, 82, 210, 328 | Cattle, Human | 1960, 1961, 1980, 2011 |
Inner Mongolia | 36 | B. abortus bv. 1, 3, 6 | 28, 30, 36, 37 112, 116, 117 | 71, 72, 75, 78, 82 210, 326, 328, 331 | Cattle, sheep, Human, Goat | 1956–1988 |
The genetic diversity profile of B. abortus based on the HGDI
Based on HGDI analysis, three loci (bruce06, 08, and 12) showed no diversity (HGDI = 0.0000) and bruce55 showed the highest diversity in all loci of panel 1, with a value of HGDI of 0.6515. The lowest value of HGDI in panel 2B was bruce16 (HGDI = 0.2576), the HGDI value in other four loci were > 0.5705, and the HGDI value of panel1, MLVA-11, and MLVA-16 was 0.7820, 0.8196, and 0.9853, respectively (Table 2).
Table 2
Allelic types and HGDI of B. abortus for 16 loci in this study.
Panel and Locus | HGDI values |
Bruce06 | 0.0000 |
Bruce08 | 0.0000 |
Bruce11 | 0.4034 |
Bruce12 | 0.0000 |
Bruce42 | 0.0776 |
Bruce43 | 0.1139 |
Bruce45 | 0.0396 |
Bruce55 | 0.6515 |
Bruce18 | 0.1701 |
Bruce19 | 0.2204 |
Bruce21 | 0.0396 |
Bruce04 | 0.6392 |
Bruce07 | 0.7905 |
Bruce09 | 0.7719 |
Bruce16 | 0.2576 |
Bruce30 | 0.5705 |
Panel 1 | 0.7820 |
MLVA-11 | 0.8196 |
MLVA-16 | 0.9835 |
Mlva-16 Genotyping Characteristics
In panel 1, 10 genotypes were observed, of which 7 are known, including 116 (n = 1), 30 (n = 4), 37 (n = 5), 112 (n = 13), 117 (n = 15), 28 (n = 17), and 36 (n = 39). The remaining three unassigned genotypes were Ba8-1 (n = 2) (4-5-3-12-2-1-3-2), Ba8-2 (n = 2) (4-5-3-1-2-3-1-3-2), and Ba8-3 (n = 2) (4-5-3-1-2-3-1-5-2) (Fig. 1). In MLVA-11, 17 genotypes were found, 13 of which were of known genotypes, namely, 71 (n = 1), 83 (n = 1), 181 (n = 1), 210 (n = 9), 331(n = 1), 327 (n = 3), 75 (n = 4), 78 (n = 4), 326 (n = 4), 77 (n = 5), 82 (n = 11), 328 (n = 12), 72 (n = 38), and 4 novel genotypes: Ba11-1 (n = 1), Ba11-2 (n = 1), Ba11-3 (n = 2), and Ba11-4 (n = 2) (Fig. 1). Genotype 72 was distributed in seven regions, the higher diversity of MLVA-11 genotype was observed in strain from Inner Mongolia, Xinjiang Province, Hebei Province, and Sichuan Province (Table 1). However, the novel MLVA-11 genotype was found in Ningxia, Heilongjiang Province, and Hebei Province (Table 1). Using the complete MLVA-16 loci, 100 strains were sorted into four groups (I–Ⅳ) and 65 MLVA-16 genotypes (G.T.) had a 50% similarity coefficient. Both biovar 1 and 2 were fell into group Ⅱ; the other five biovars 3, 5, 6, 7, and 9 were clustered in other three groups (I, Ⅲ, and Ⅳ), of which group I contained six subgroups (a–f) (Fig. 1). The 54 strains consisted of 19 shared genotypes that contained 2–8 strains, and 46 strains of an independent genotype, each present a single strain. Eighteen out of 19 strain-shared genotypes comprised strains from the same province; only one shared genotype (GT48) contained five strains obtained from four provinces (Fig. 1).
Geographic origin features of Chinese B. abortus strains on a global scale
Among 17 MLVA-11 genotypes, seven were shared genotypes (72, 75, 82, 83, 181, 210, and 328) comprising strains from 2 to 10 countries, and the remaining 10 genotypes were single genotypes that were exclusively found in Chinese strains. The genotype 72 (n = 38) was the predominant population and accounted for 38% (38/100), 12 in genotype 328, 11 in genotype 82, and 9 in genotype 210. MLVA-11 genotype 72 was shared by strains from six countries, including France, Germany, Italy, Kazakhstan, Portugal, and China. Genotype 82 comprised strains from 10 countries, including Brazil, Costa Rica, France, Germany, Italy, Kazakhstan, Portugal, South Korea, the United States, and China. Genotype 210 consisted of strains from four countries, Costa Rica, Italy, United States, and China. Genotype 78 was shared by strains from England, the United States, and China. Genotype 83 was shared by strains from Brazil, Costa Rica, England, and China. Genotype 75 included strains from Brazil and China. Genotype 181 consisted of strains from Portugal and China. However, another 10 single genotypes were exclusive of strains from China (Fig. 2).
Worldwide Phylogenetic Analysis Based On Both Mlva-16 And Wgs-snp
In present study, 1,625 strains were sorted into three groups (A–C), and Chinese strains fell into group A and clustered together with strains from Italy, Kazakhstan, and Brazil, but had no sharing of the MLVA-16 genotype was observed (Fig. 3). Whole-genome SNP analysis showed that 65 B. abortus strains were grouped into seven clades (Ⅰ–Ⅶ) (Fig. 4); 16 Chinese strains were grouped into five clades (Clade Ⅰ, Ⅲ, Ⅳ, Ⅵ, and Ⅶ). Clade Ⅰ was composed of two Chinese strains and one strain from Kenya; clade Ⅲ included strains from China, Poland, and Spain; clade Ⅳ included strains from China, South Korea, and USA; clade VI included strains from China, Italy, and Greece. Clade Ⅶ was composed of 19 strains from nine countries, including Uganda, Iraq, Russia, Georgia, Spain, Italy, Egypt, Mongolia, and China. These strains formed a ladder-like phylogram. However, most strains (n = 8) from China were found in clade Ⅶ and were the most similar to strains from Russia and Mongolia (Fig. 4).