The absence of a nutritional effect suggests the cAMP-CRP regulatory system is influenced by temperature. Additional cellular processes could also be contributing to the observed behaviors including temperature dependent changes in multidrug pump expression , temperature dependent changes in cellular membrane properties  and temperature dependent changes in growth rate. A biofilm grown at 21°C for 6 hours would be
less established than a biofilm grown at 37°C for 6 hours. While Fig. 8 shows a growth stage dependent change in ampicillin tolerance, it does not show a growth stage dependent change in kanamycin tolerance when glucose is present. The changes in antibiotic tolerance at 21°C were for both kanamycin and ampicillin suggesting it is not just a growth stage dependent phenomenon. Interrupting AI-2 QS had varied and unpredictable effects AZD1480 clinical trial on antibiotic tolerance. A growing body S63845 datasheet of research suggests different organisms use QS for different purposes and that QS effects can be quite diverse. For instance, a recent review
highlights that the luxS based AI-2 QS system can increase, decrease, or have no effect on biofilm formation depending on the organism or strain . While acylhomoserine lactone (AI-1) based QS interference has been generally successful with Pseudomonas aeruginosa [23, 48], accessory gene regulator (Agr) based QS interference with Staphylococcus
aureus and Staphylococcus epidermidis can make the microbes more resilient to antibiotic treatments (reviewed in ). The current study demonstrates a large increase in antibiotic tolerance when the AI-2 QS system was disrupted however, this effect was gene and context dependent (Fig. 7). For unknown reasons, the ΔlsrK strain behaved analogous to the wild-type culture when perturbed with glucose. The ΔluxS strain was further characterized and found not to display a glucose dependent antibiotic tolerance response (Additional file1) implying a disruption of Montelukast Sodium a portion of the glucose repression circuit. The ΔluxS strain did display catabolite repression based diauxic growth. The strain was grown on defined M9 medium containing both glucose and Epigenetic Reader Domain inhibitor xylose. Like the wild-type strain, the ΔluxS strain preferentially consumed glucose (data not shown). The data from this study do not support pursuing a strategy of AI-2 quorum sensing interference as an antifouling approach with E. coli. Conclusions Robustness analysis revealed that colony biofilm antibiotic tolerance is very sensitive to culturing perturbations. These tolerance responses can vary based on single or aggregate perturbations and are, in many cases, not predictable. The collective data represents both challenges and opportunities for the rational design of anti-biofilm strategies.