Nor Amdan, Nur Asyura Binti; (2018) Investigation into mechanisms of biofilm formation by Klebsiella pneumoniae. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Klebsiella pneumoniae is a Gram-negative opportunistic pathogen that normally causes nosocomial infections such as urinary tract infections, septicaemia, and respiratory tract infections. K. pneumoniae has become progressively resistant to the vast majority of antibiotics, and treatment of these particular infections is very challenging. At present, the emergence of antibiotic resistance is a widespread phenomenon that has been established as a major global healthcare threat. The ability of K. pneumoniae to form biofilms is known as one of the most important factors that contributes to the spread of this antibiotic-resistant bacterium. Due to that fact, understanding the mechanisms behind biofilm formation by K. pneumoniae is of the utmost importance. Numerous studies have shown that sub-inhibitory concentrations of antibiotics could induce biofilm formation by clinically important pathogens, for example, Escherichia coli, Pseudomonas aeruginosa, and Staphylococcus aureus. In this study, we report for the first time on the effect of sub-minimum inhibitory concentrations (sub-MICs) of gentamicin and ciprofloxacin on biofilm formation by K. pneumoniae. In addition, by using biofilm inhibition and disruption assays, we have also assessed the role of proteins in formation and composition of K. pneumoniae biofilms upon cultivation in nutritious and nutrient-poor media. As well as proteins, the role of polysaccharides and extracellular DNA was also determined. Furthermore, the role of type 1 fimbriae (T1F) in biofilm formation by K. pneumoniae was also determined. Transcription of fimA (the major subunit of T1F) is phase variable, as its promoter is on an invertible DNA element, fimswitch (fimS). We investigated the orientation of fimS in all K. pneumoniae strains used in this study, in planktonic and as biofilm cells, upon cultivation in tryptic soy broth (TSB) and artificial urine medium (AUM). Finally, we have also determined the role of outer membrane porins, OmpK35 and OmpK36 in biofilm formation by K. pneumoniae. We developed isogenic mutants of ∆ompK35 and ∆ompK36 strains. The capacity to form biofilms by the mutant strains compared to parental strains was examined in two different models, a microtitre plate model and a model using catheter pieces. Currently, we still lack a full understanding on the mechanisms of biofilm formation by K. pneumoniae which is important in order to develop new treatments to reduce the threat of biofilm-mediated infections by K. pneumoniae.

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