前噬菌体对猪链球菌毒力、环境适应性、耐药性及代谢活动的影响

Effects of Prophage on Virulence,Environmental Adaptability,Drug Resistance and Metabolic Activity of Streptococcus suis

旨在了解和掌握前噬菌体与猪链球菌(Streptococcus suis,SS)毒力、环境适应性、耐药性及代谢活动之间的关系,本研究对前噬菌体阳性菌株(简称阳性菌)与前噬菌体阴性菌株(简称阴性菌)进行了致病性试验、LD_(50)的测定、组织荷菌数的测定及病理组织学观察、生物被膜(BF)形成能力的测定、药敏试验和转录组测序。结果显示:39株阳性菌和7株阴性菌中,各有11株和2株菌对小鼠致死率≥80.0%,11株阳性菌LD_(50)为8.4×10^(8)~2.36×10^(9)CFU·只^(-1),2株阴性菌LD_(50)分别为1.88×10^(9)、2.72×10^(9)CFU·只^(-1),阳性菌与阴性菌之间LD_(50)差异不显著(P>0.05)。LD_(50)为8.4×10^(8)CFU·只^(-1)的阳性菌攻毒后小鼠各脏器(肺、肝、脾、肾、心、脑)组织荷菌数最多,病理变化最明显,LD_(50)为2.72×10^(9)CFU·只^(-1)的阴性菌攻毒后小鼠各脏器组织荷菌数最少,病理变化最轻微;BF形成阳性率阳性菌为97.4%,阴性菌为100.0%;阳性菌和阴性菌均对四环素、红霉素、克林霉素、阿奇霉素、头孢曲松、多西环素呈现多重耐药,二者的耐药性无显著差异(P>0.05);相较于阳性菌,毒力相关基因、BF形成相关基因、耐药基因、脂肪酸生物合成通路以及精氨酸和脯氨酸代谢通路中所涉及到的相关基因在阴性菌中多为上调表达。综上表明:前噬菌体存在与否与SS的毒力增强或减弱、耐药性的高或低以及BF的形成能力之间未有明显相关性;但前噬菌体的存在会引致与SS脂肪酸生物合成以及精氨酸和脯氨酸代谢过程中相关联基因的表达下调,从而造成脂肪酸和氨基酸代谢水平降低。

To understand and master the relationship between prophage and virulence,environmental adaptability,drug resistance and metabolic activity of Streptococcus suis(SS),in this study,the pathogenicity test,LD_(50) test,the number of bacteria loaded in tissue,histopathological observation,biofilm formation(BF)ability test,drug sensitivity test and transcriptome sequencing were carried out for the prophage positive strains(positive bacteria for short)and prophage negative strain(negative bacteria for short).The results showed that among 39 strains of positive bacteria and 7 strains of negative bacteria,11 strains and 2 strains of bacteria had a lethal rate of more than 80.0%,The LD_(50) of 11 positive bacteria ranged from 8.4×10^(8) to 2.36×10^(9)CFU·piece^(-1),and that of 2 negative bacteria were 1.88×10^(9) and 2.72×10^(9)CFU·piece^(-1),respectively.There was no significant difference in LD_(50) between positive and negative bacteria(P>0.05).After being challenged with positive bacteria with LD_(50) of 8.4×10^(8) CFU·piece^(-1),the number of bacteria in the organs(lung,liver,spleen,kidney,heart and brain)of mice was the most,and the pathological changes were the most obvious,after being challenged with the negative bacteria with LD_(50) of 2.72×10^(9) CFU·piece^(-1),the number of bacteria in each organ tissue of mice was the least,and the pathological changes were the least;The positive rate of BF formation was 97.4%for positive bacteria and 100.0%for negative bacteria;Both positive and negative bacteria showed multiple drug resistance to tetracycline,erythromycin,clindamycin,azithromycin,ceftriaxone and doxycycline,and there was no significant difference in drug resistance between them(P>0.05);Compared with positive bacteria,virulence related genes,BF formation related genes,drug resistance genes,fatty acid biosynthesis pathway and arginine and proline metabolism pathway related genes were up-regulated in negative bacteria.the results showed that there was no significant correlation between the presence or absence of prophage and the increase or decrease of SS virulence,high or low drug resistance and BF formation ability;However,the presence of prophage will lead to the down-regulation of genes associated with SS fatty acid biosynthesis and arginine and proline metabolism,resulting in the reduction of fatty acid and amino acid metabolism.