Other genes of interest include pagP , a PhoPQ-regulated palmitoyl transferase for lipid-A ; sdiA , a regulator of quorum-sensing and virulence ( Ahmer et al. 1998 ; Volf et al. 2002 ) ; permeases of oligopeptides , such as oppF and oppB ( Goodell and Higgins 1987 ; Orchard and Goodrich-Blair 2004 ) ; and several genes involved in drug resistance , such as emrE and nudF .