Risk assessment for the spread of Serratia marcescens within dental-unit waterline systems using Vermamoeba vermiformis

Vermamoeba vermiformis is associated with the biofilm ecology of dental-unit waterlines (DUWLs). This study investigated whether V. vermiformis is able to act as a vector for potentially pathogenic bacteria and so aid their dispersal within DUWL systems. Clinical dental water was initially examined for Legionella species by inoculating it onto Legionella selective-medium plates. The molecular identity/profile of the glassy colonies obtained indicated none of these isolates were Legionella species. During this work bacterial colonies were identified as a non-pigmented Serratia marcescens. As the water was from a clinical DUWL which had been treated with Alpron™ this prompted the question as to whether S. marcescens had developed resistance to the biocide. Exposure to Alpron™ indicated that this dental biocide was effective, under laboratory conditions, against S. marcescens at up to 1x108 colony forming units/millilitre (cfu/ml). V. vermiformis was cultured for eight weeks on cells of S. marcescens and Escherichia coli. Subsequent electron microscopy showed that V. vermiformis grew equally well on S. marcescens and E. coli (p = 0.0001). Failure to detect the presence of S. marcescens within the encysted amoebae suggests that V. vermiformis is unlikely to act as a vector supporting the growth of this newly isolated, nosocomial bacterium

Developing an ecologically relevant heterogeneous biofilm model for dental-unit waterlines

This study monitored the biodiversity of microbes cultured from a heterogeneous biofilm which had formed on the lumen of a section of dental waterline tubing over a period of 910 days. By day two bacterial counts on the outlet-water showed that contamination of the system had occurred. After 14 days, a biofilm comparable to that of clinical waterlines, consisting of bacteria, fungi and amoebae had formed. This showed that the proprietary silver coating applied to the lumenal surface of the commercial waterline tubing failed to prevent biofilm formation. Molecular barcoding of isolated culturable microorganisms showed some degree of the diversity of taxa in the biofilm, including the opportunistic pathogen Legionella pneumophila. Whilst the system used for isolation and identification of contaminating microorganisms may underestimate the diversity of organisms in the biofilm, their similarity to those found in the clinical environment makes this a promising test-bed for future biocide testing

Free will, punishment and criminal responsibility

Retributive attitudes are deeply held and widespread in the general population and most legal systems incorporate retributive elements. It is probably also the dominant theory of punishment among contemporary philosophers of criminal justice. However, retributivism relies on conceptions of free will and responsibility that have, for millennia, fundamentally divided those who have thought seriously about the subject. Our legal system upholds the principle that the responsibility of the offender has to be proven beyond reasonable doubt, before the accused can be punished. In view of the intractable doubts surrounding the soundness of retributivism’s very conception of responsibility, my thesis argues that it is ethically dubious to punish individuals for solely retributive reasons. Instead, my thesis proposes that a person should only be punished if the main theories of punishment agree that punishing that person is appropriate – I call this ‘the convergence requirement’. This approach, I argue, is in accordance with the considerations underlying the beyond reasonable doubt standard. In addition to considering the question of ‘whom to punish’ my thesis considers what methods of responding to criminal behaviour are acceptable. In particular, it attempts to explain, without appealing to the contested notions of free will or retributive desert, what is problematic about ‘manipulative’ methods of dealing with criminal offenders (focussing in particular on the possibility of modifying their behaviour through neurological interventions). The final part of this thesis also gives an overview of some of the practical implications for Scots criminal law of taking doubts about free will and retributivism seriously. Given the severe treatment that offenders undergo within the Scottish penal system (e.g. deprivation of liberty, stigma) and the high rate of recidivism, it is important to consider whether our current penal practices are justified, what alternatives are available and what goals and values should guide attempts at reforming the system