Experimental Observation Of Survival And Animal Laboratory Study On The Pathogenecity Of Backusella Circina Var.circina

Objective: Backusella belong to the Eumycota, zygomycetes subphylum, Mucorales, widely distributed in the nature. the vast majority of the mucorales distribution in organic matter, soil and animal corpses. B.circina var. circina for one variant of Backusella, is a multi-line group, and with Actinomucor, Mucor and Rhizomucor, has close pedigree relationship[1].In recent years domestic and foreign related Backusella infections reports gradually increased. But there is no report on human infection in the literature. Strains used in this study comes from one case of facial skin lesions in patients with leukemia in our hospital in 2009, identified preliminarily as Backusella circina by the Chinese academy of sciences institute of microorganisms. As currently gene sequence has been detected, it is Renamed B. circina var. circina.In this study, with the method of animal experiments, the mice are to be infected with the suspension of strain. On the one hand by observing the survival time and deaths of mice, observers can understand the Pathogenicity size in mice; On the other hand, By observing the general performance of the internal organs of mice, tissues fungal culture, how much of the major organs of mice will be infected with the situation can be observed.Methods: 1 Experimental observation of survival 1.1 Establishment of animal model suffered from systemic infection of B.circina var. circina. The preserved fungi were restored virulence, then inoculated on the Sabouraud′s Agar, at 27℃ for three days. With two methods, sterile saline is used to prepare a fungal suspension, mycelium content and concentration of fungal suspension are different. In intraperitoneal injection ways inoculated with different to immune status mice. 1.2 The observation of mortality Continuous observation of survival and natural death within four weeks after mice infected in each group, record the date of death and the number of deaths. 2 Pathogenicity test of animal 2.1 Observing the infectious organs Dissect mice of natural death at different times and the mice sacrificed after the end of observation, took the heart, liver, spleen, lung and kidney under sterile conditions, and observed their changes of size, color, and so on. 2.2 Tissues fungal culture Under sterile conditions, the infected tissues were grinded and subcultivated into test tubes containing Sabouraud′s Agar. After being cultured at 27 ℃ for one weeks, observe the growth of colonial morphology and shape, In addition, Colonies were picked into a wet piece of mycelium and spore morphology observed under an optical microscope.Results: 1 The results of survival test 1.1 The survival of mice after infection Mice of different immune status were inoculated with different concentrations and there was no mycelium fragments of fungal suspension, their mental state, food intake and activity levels did not change significantly. The mice with different immune status were inoculated with higher mycelium content of fungal suspension,no matter the size of the concentrations, their mental state deteriorated significantly, food intake and activity levels significantly reduced. The mice with different immune status were inoculated with lower mycelium content of fungal suspension,varies with the concentration of fungal suspension mice in each group were different reactions, in which the immune normal mice at low concentrations, their mental state, food intake and activity levels had no significant change. 1.2 The higher the concentration of fungal suspension inoculation in same mycelium content, The higher the proportion of hyphae and spores inoculated mice under the same concentration of fungal suspension,the shorter the time required for all deaths,which has no significant relationship with the immune status,Wherein the inoculation mycelium and spores ratio at 2: 1, and at a concentration of 1~1.5×106CFU/ml fungal suspension mice all died within 6 days. 1.3 Keep observing until the end of four weeks, mice were inoculated with no mycelium fragments of fungal suspension, their survival rate were 100%. Under the same immune status and fungal suspension concentration, the higher hyphae and spores ratio inoculated, the higher the number of deaths and the lower survival rates of mice;Under the same immune status and hyphae and spores ratio, the higher fungal suspension concentration inoculated, the higher the number of deaths and the lower survival rates of mice. 2 The results of Pathogenicity test 2.1 General changes in various organs On the liver surface of the portion taken from the mice of natural death at different times, visible tip to miliary size white purulent lesions could be seen; lungs occasionally saw scattered in the tip size white purulent lesions; liver, spleen, kidney varying degrees of edema. After four weeks to observe the surface of the organs of mice sacrificed;no obvious lesions of infection. 2.2 The results of Tissues fungal culture Natural death visceral tissue of mice cultured for 3 days to see part of the organ colony growth, the various organs and tissues inverse fungal cultures appeared at the end of observation were positive results, and its colony morphology and microscopic morphology are the same as the original strain.Conclusion:1 Backusella circina var.circina are opportunistic pathogens, likely to be infected at the time of decreased immunity;2 Mainly from the mycelium fungus pathogenicity;3 Both Pathogenicity and aggressiveness are strong, no matter the size of concentration in this study, and it can cause damage to the body under the different immune status;4 By intraperitoneal injection routes animal model suffered from systemic infection of B.circina var.circina can be successfully established.