Team:Tongji China/P.A.
Background
P. aeruginosa
Now, we are concerning about the spices and strain of the bacteria involved in our project. We choose Pseudomonas aeruginosa in the strain of PAK-JΔ9 which is an attenuated strain, for it has many advantages varying from efficiency to safety. To be specific, we will introduce the course of searching for this ideal strain step by step to you. The Reason that we choose P. aeruginosa
At the first time, we decided to use Type III secretion system (T3SS) to activate the patient's immune system, because it seems to be a practical way. So which type of bacteria can we choose? We went through carefully investigation and finally focused our attention on Pseudomonas aeruginosa (P. aeruginosa).
1 We already knew that T3SS is one of the features that belongs to Gram-negative bacteria, and there are significant differences between every species. As a result, some important spices which are widely used in attenuated vaccine such as Listeria Monocytogenes are out of the range because of its classification.
2 Referring to a large number of articles, we discovered that P. aeruginosa's T3SS shows little differences associated with the change of pH value, which is a distinct feature of intestinal environment, while others' don't. T3SSs can be divided into two groups by the homologue of its core proteins. IpaD, BipD, and SipD have similar physical properties such as stability and spectroscopic measurements and they fall into one subfamily, while LcrV and PcrV also share these properties together. Proteins in IpaD subfamily manifest three distinct structural forms from pH 3 to 8 which result in enormous decline in ability of T3SS. In contrast, LcrV and PcrV show little differences in structures associated with the change of pH value, as well as its property. Because high pH value is a feature of intestinal environment, we can assume that bacteria whose T3SS is construed with LcrV subfamily as the core can better serve in intestinal environment. And, of course, P. aeruginosa is one of them.
3 When it comes to T3SS, there are some bacteria strains that are widely used in research, such as Salmonella spp., Yersinia spp. and also P. aeruginosa. Comparing from their pathogenicity, wild type Salmonella and Yersinia are all pathogenic bacteria. Salmonella would cause Gastroenteritis fever and Yersinia would cause Enterocolitis. But the wild type P. aeruginosa is opportunistic pathogenic, which means that it will be safer and less toxic in terms of the human disease treatment.
4 There are already some researches using attenuated P. aeruginosa to deliver some proteins of interest. The common way they use is directly injecting the bacteria into vein. After injection, P. aeruginosa would gather in two organs, liver and spleen, which are the places the immune cells are concentrated. So we indicate that the P. aeruginosa may be more likely to attach the immune cells, which are also our target cells.
5 P. aeruginosa has been proved not belong to the inherent germs in our intestine. So when P. aeruginosa enters the intestine, it would be attacked by the immune system not only in intestinal, but also systemic compartments. Moreover, the inherent germs in our intestine could also be a threat to it. The role of intestinal microbiota in this course is proved by a trial conducted between fecal microbiota transplantation mice and normal mice. The trial shows a significant difference of colonization ratio between these two groups, and we can surmise that it is resulted from the differentiation of intestinal microbiotas. If these microbiotas do make a difference, they are more likely to be regarded of influencing the colonization of P. Aeruginosa. So the attenuated P. aeruginosa cannot stay in the intestine for too long and the majority of them will be eliminated in the intestine.
©Dennis Kunkel Microscopy
Electron microscopy picture of Pseudomonas aeruginosaP. Aeruginosa.
Pseudomonas aeruginosa is one of the ubiquitous gram-negative rods which we can see in many environments. It is also called hospital-acquired infections because it has multidrug-resistance which ensures its survival state. Also, P. aeruginosa is an opportunistic extracellular pathogen to human, because this bacterium is responsible for some diseases such as acute infections with burn wound and its primary hazard is the infections during surgery.
The way of attenuating
So, won't such a dangerous pathogen do harm to patients in their oral way? Of course not. Description above is for the wild-type P. aeruginosa, while the bacteria we use is modified to ensure its safety. This strain is called PAK-JΔ9, an advanced type comparing to PAK-JΔ8, whose added feature makes it a kind of auxotrophic bacterium. P. aeruginosa Δ8 is a genetically engineered attenuated strain, belonging to the fourth safety level with the lowest degree of damage, which is the same level as the vaccine for human body use. The strain is attenuated by deleting all its virulence factors by genetic manipulation on the basis of P. aeruginosa. The biosafety laboratory level required for the experimental activities of this species is BSL-1/ABSL-1 (laboratory/animal laboratory), the lowest biosafety level. According to the classification and packaging requirements of ICAO document Doc9284 "Technical Specifications for the Safe Transport of Dangerous Goods", the species belongs to Class B transport requirements, and the corresponding UN number is UN 3373 for packaging and transportation. The μA gene of this strain is mutated so they cannot live without the presence of D-Glutamate. But the human body does not contain D-Glutamate, so this P. aeruginosa strain cannot be amplified in the human body and survive for a long time, nor can they survive in the natural environment.
To know more about the safety of the P. aeruginosa, you could go to the Safety-P. aeruginosa.
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