Why Are Some Pathogens Hard To Kill

Escherichia Coli

Most invading pathogenic bacteria are effectively dealt with by the body’s immune system, with immune cells sweeping towards the site of infection and engulfing the invading cells or killing them through other means.

Some pathogens, however, are adept at resisting or avoiding the immune response. An example is certain types of Escherichia coli.

As part of the hunt for alternative ways of killing pathogenic organisms, and in light of the problems faced with the decline in the number of suitable antibiotics, researchers have been looking at an organism called Bdellovibrio bacteriovorus. B. bacteriovorus is efficient at engulfing cells of pathogenic E. coli and destroying it. The problem is, E. coli can often avoid being captured and devoured.

Bacteriovorus is found in the human gut, among other places. It has a high potential as a biocontrol agent because it acts as a ‘parasite’ to other bacteria of a similar structure, meaning that it can potentially eliminate harmful organisms.

To find out why E. coli can avoid being caught, researchers based at the University of Jerusalem have run a series of experiments.

The study looked at the soil environment. Here, various chambers were constructed and the interaction of the two microorganisms considered. It was found that in the open environment, E. coli was easily overwhelmed and destroyed within a few hours. However, in more closed environments, the pathogen remained robust.

The researchers think that in a more fragmented environment, E. coli is able to hide and avoid detection. This is because the cells form a biofilm, where they stick together and extrude a protective sticky layer.

Overcoming this defensive mechanism by E. coli is seen as key to developing a new generation of antimicrobial alternatives. One way being considered is to genetically modify B. bacteriovorus so it can more readily detect ‘hidden’ E. colicells.

About the author

Tim Sandle

Dr. Tim Sandle is a chartered biologist and holds a first class honours degree in Applied Biology; a Masters degree in education; and has a doctorate from Keele University.