Biofilms have been implicated in recurring nosocomial infections, often associated with high mortality rates. Crucially, they have also been shown to be highly tol- erant to commonly used antibiotics. In this work I investigated how the biofilm lifestyle protected bacterial cells from antibiotics. I engineered an environmental Escherichia coli isolate to express a clinically relevant blaCTX-M-14 gene which con- fers resistance to β-lactam antibiotics, including third generation cephalosporins. β-lactamases are considered to be potential social traits, i.e. public goods whose advantages are shared between bacterial cells. I used the resulting experimental system to test three central hypotheses: (a) social interactions between bacterial strains are enhanced in biofilms compared to planktonic cultures, and coopera- tion is facilitated when strain segregation is permitted, (b) the biofilm structure, including the matrix and cell localisation, affects biofilm tolerance & (c) the phys- iological state of bacteria in biofilms influences antibiotic tolerance. I found that biofilms facilitate cheating but the dynamics of this behaviour did not always agree with theoretical work on social evolution; in particular, cooper- ative cells did not benefit from high frequencies as was expected. Additionally, I used Optical Coherence tomography (OCT) and fluorescence microscopy to in- vestigate the colony biofilm structure and strain localisation within the biofilms, and observed distinctive responses to antibiotic treatment. This was the first time colony biofilms were observed it their entity using microscopy. Finally, I concluded that the metabolic rates of cells did affect antibiotic tolerance but a straightforward correlation between metabolic rates and growth rates could not be established. Taken together, my results suggest that both the sociality of β-lactamase expression and the intrinsic tolerance associated with the biofilm lifestyle may be significant factors in E. coli biofilm resistance to β-lactam an- tibiotics. This has implications for the development of antimicrobial strategies against Gram-negative bacteria.
|Award date||1 May 2017|
|Publication status||Unpublished - 2017|