Molecular Epidemiology Of Pasteurella Multocida From Swine In Some Provinces Of China

P.multocida is a common symbiotic bacteria or opportunistic pathogens.It has a wide disease and host spectrum,and can usually be isolated from the upper respiratory tract.In terms of animal husbandry,it is considered a primary pathogen in specific diseases like fowl cholera in birds,atrophic rhinitis in swine,hemorrhagic septicemia in cattle,snuffles in rabbit,etc.In addition,P.multocida is also a zoonotic pathogen.Human infections with P.multocida predominantly occur following cat-and dog-inflicted injuries resulting in cellulitis and lymphangitis.P.multocida strains have classically been differentiated using serological techniques.Strains can be classified into five capsular serogroups(A,B,D,E,and F)and into 16 somatic or lipopolysaccharide(LPS)serovars.In addition,specific diseases are often associated with specific serotypes,for example,swine plague is often associated with type A strains.However,the molecular and cellular basis for the association of these specific serotypes with host disease remains unclear.In this study,P.multocida strains associated with porcine pneumonia were isolated and identified,then conducted capsular multiplex PCR,polysaccharide multiplex PCR,virulence gene detection,multiple site sequence typing(MLST).In order to understand the genetic diversity,population structure and molecular characteristics of these strains,the study was conducted.The main contents of this paper are as follows.1.Isolation and identification of pneumonic P.multocida in swineFrom 2015 to 2016,a total of 115 strains of P.multocida were isolated from 1597 clinical diseased lungs in our country,and total isolation rate is 7.2%.Typed by capsular multiplex PCR,the porcine pneumonic P.multocida belonged to three capsular types: A57(50%),D 53(46%),and nontypable 5(4%).2.LPS genotyping of pneumonic P.multocida in swineFor 115 LPS genotype detection,26(22.6%)were genotype L3 and 89(77.4%)were genotype L6.Interestingly,all of the capsular type D strains produced the L6 genotype LPS.3.Distribution of virulence genesAmong the 23 kinds of virulence genes tested within the 115 pneumonic P.multocida,all of the isolates were positive for sodA(100.0%),sodC(100.0%),exbB(100.0%),exbD(100.0%),ompA(100.0%),ompH(100.0%),oma87(100.0%),hsf-2(100.0%),fimA(100.0%),ptfA(100.0%),and tonB(100.0%).There were some virulence genes with a low detection ratio such as toxA(2.6%)and tbpA(0).The detection of pfhA?tadD?pmHAS?hgbA?hsf-1?hgbB between capsular types A and D strains showed highly statistically significant difference(P<0.05).According to LPS genotypes,the distribution of pfhA?tadD?pmHAS?hgbA?nanH?hgbB?nanB between the two LPS genotype strains was highly significantly different(P<0.05).In this study,we first found that the detection of pfhA might be only related to the LPS genotype.4.MLST of pneumonic P.multocida in swineIn this study,23 strains of P.multocida were tested in different provinces.The results showed that ST3,ST10 and ST11 were the main ST types,and there are more than one STs being prevalent in many provinces.ST11 are distributed in seven provinces in China,indicating their widespread distribution in China.This highlights the need for epidemiological surveillance of this particular genotype of P.multocida.It is noteworthy that three strains of toxigenic P.multocida,which were isolated from different provinces(Shanxi,Hubei,Guangdong)belong to the ST11 type,and 8 previously isolated toxigenic P.multocida is also the ST11 type strains.ST11 may be the main ST type of atrophic rhinitis in Chinese herds.