Sub-inhibitory rifampicin

A while back I wrote a post interpreting the messy results of some microarray analysis. The analysis was looking for effects of treating H. influenzae cells with very low concentrations of two antibiotics (rifampicin and erythromycin). These concentrations do not detectably inhibit cell growth, but rifampicin appeared to be significantly increasing the expression of some genes.

Our criterion for 'maybe significant' was that the gene should be increased at least two-fold in all three of the arrays we examined. The collaborator's technician has now gone back into the data to see if related genes are also induced, at levels just too low to meet our cutoff. Her results confirm that the antibiotic affects a whole class of genes. Our collaborator tells me that an effect on these genes is unprecedented, so on we go.....