Interference in quorum sensing signal transmission amongst microbial species

Antibiotics are usually studied on pure cultures of a single bacterial strain, whereas multi-species communities that inhabit human niches and the biosphere are generally ignored. The modification of quorum sensing (QS) is investigated in a system involving a co-existing signal producer and sensor bacterial cells. A pure culture of merely one bacterial species is quite rare in any niche. The interactions of different bacterial species may therefore be of special importance in pathogenicity, antibiotic resistance and signal transmission.In the present study the authors investigated the QS in model experiments involving several Gram-positive and Gram-negative bacterial species isolated from human infections or laboratory strains. The effects of various compounds on QS were studied in mixed bacterial populations during the incubation period of 24-48 h. As the simplest example of co-existing cell populations, the N-acyl homoserine lactone producing Ezf 10-17 was applied with Chromobacterium violaceum 026 as sensor.The signal of QS transmission between the co-existing QS system and pathogenic bacteria isolated from various patients was found to be modified by certain bacterial cells. The bacterial-bacterial interactions in a mixed flora can change the classical signal transmission in the microbial community and should therefore be taken into consideration in rational chemotherapy.