Blood poisoning bacteria (Pasteurella multocida) colonies (white) being cultured on an agar growth medium (red) in a petri dish. Blood poisoning (or septicaemia) can be caused by several bacteria. This one, found in the upper respiratory tracts of many animals, can be transmitted to humans by a bite. It is very sensitive to penicilin. Grown on Columbia blood agar. Blood agars are nutrient agars enriched with blood for bacterial growth.