Quorum sensing or QS essentially is how bacteria talk to eack other. It is mediated through small molecules. I got to hear two excellent QS scientists, Dr Bassler from Princeton and Dr Losick from Harvard, in 2007. They seem to bring the excitement about basic bacterial research back to all the audience.

Have a look at some of their reviews and papers.

"Bacterially Speaking"
http://www.cell.com/content/article/abstract?uid=PIIS0092867406004338

A paper in Aug1, 2008 issue of Microbiology describes QS in human bacterial pathogen P. aeruginosa.

Role of quorum sensing by Pseudomonas aeruginosa in microbial keratitis and cystic fibrosis
Microbiology ; 154: 2184 - 2194

more info on QS:
http://www.nottingham.ac.uk/quorum/index.htm