Bacterial cells within biofilms and cell aggregates show increased resistance against chemical stress compared with suspended cells. It is not known whether bacteria that co-habit biofilms formed by other bacteria also acquire such resistance. This scenario was investigated in a proof-of-principle experiment with Pseudomonas aeruginosa strain PAO1 as cell aggregate-forming bacterium and Escherichia coli strain MG1655 as potential co-habiting bacterium equipped with an inducible bioluminescence system. Cell aggregation of strain PAO1 can be induced by the toxic detergent sodium dodecyl sulfate (SDS). In single cultures of strain MG1655, bioluminescence was inhibited by the protonophor carbonylcyanide-m-chlorophenylhydrazone (CCCP) but the cells were still viable. By applying CCCP and SDS together, cells of strain MG1655 lost their bioluminescence and viability indicating the importance of energy-dependent resistance mechanisms against SDS. In co-suspensions with strain PAO1, bioluminescence of strain MG1655 was sustained in the presence of SDS and CCCP. Image analysis showed that bioluminescent cells were located in cell aggregates formed by strain PAO1. Thus, cells of strain MG1655 that co-habited cell aggregates formed by strain PAO1 were protected against a severe chemical stress that was lethal to them in single cultures. Co-habiting could lead to increased survival of pathogens in clinical settings and could be employed in biotechnological applications involving toxic milieus.