Blood poisoning is a layman's term for the sepsis.Sepsis is a life threatening condition in which there is growth of bacteria and other toxic products in the body with a severe inflammatory condition in the body called as Systemic inflammatory response syndrome(SIRS).Therefore sepsis=SIRS+ infection from the bacteria, fungi,virus,etc.Infection from the bacteria in the blood is called bacteriaemia.Infection from the fungus is called as fungaemia but if these condition get mixed with the SIRS then it is known as Sepsis.Severe sepsis is also another condition which means that sepsis+organ dysfunction while the septic shock is defined as the sepsis with the refractory arterial hypo tension or arterial hypo tension.Arterial hypo tension leads to the organ dysfunction.
 

In majority of cases sepsis is due to the infection by bacteria like gram negative bacilli(E.coli,P.aueroginosa), staphylococcus aureus,streptococcus species,Enterococcus

Candida( a fungi) also causes sepsis.These infectious agents begin infecting the organ and then enters into the blood and then it is easy to spread them in any oragan causing start of inflammatory process anywhere and then there is organ dysfunction.These process actually tried to maintain the normal conditions of the body..