Factors controlling the activity of bacteriophage UZ1 against Enterobacter aerogenes strain BE1 under simulated intestinal conditions

To study specific bacteriophage-bacteria interactions under intestinal conditions, a previously developed in vitro model system was used, combining a common pathogenic bacterium Enterobacter aerogenes BE1 and a for this bacterium specific bacteriophage, phage UZ1. As many environmental factors may influence the phage-bacterium interaction, the model was used in this study to investigate the effect of inoculum size, presence of oxygen, and physiological hindrance. When monocultures of E. aerogenes BE1/gfp with increasing inoculum size were infected with phage UZ1, complete host lysis was observed up to an inoculum size of 7 log [CFU/mL]. However, at 8 log [CFU/mL], growth was observed and phage resistant E. aerogenes BE1/gfp cells were isolated. Under simulated intestinal conditions, infection with phage UZ1 resulted in a significant decrease, up to 3 log, of E. aerogenes BE1/gfp compared to the non-phage treated control. However, no complete removal of the bacterial host could be achieved after 18 h. At high inoculum size, resistant bacteria were also isolated. However, growth curve analysis showed a reduced fitness of the phage UZ1-resistant bacteria, limiting their intestinal proliferation. Another factor responsible for differences in the bacteriolytic efficiency was the presence of oxygen. Under anaerobic conditions, the latent period increased from 20 min to more then 3 h and the burst size decreased from 70 to less than 24, compared to aerobic conditions. In conclusion, the major factors responsible for different bacteriolytic efficacy were resistance to phage infection by mutation and limited oxygen availability. Although no complete removal of the pathogen was obtained under anaerobic conditions, the strong host specificity of the phage, the decrease in bacterial concentrations and the reduced fitness of phage-resistant bacteria indicate the possibility for prophylactic use of the phage to reduce the risk of E. aerogenes BE1 infection

Choosing coalition partners in Belgian local government

Government formation is a crucial phase after elections. This article focusses on coalition formation in Belgian local government after the elections in 2006. Coalition theories have mainly been developed at the national level, but they are also applicable to the local level where there is no shortage of coalitions. This level offers the opportunity to not only test rather classic coalition theories such as minimum size theories or the coalitions' incumbency status. In a federal state like Belgium we can compare the local coalitions with coalitions made at higher levels. The results show that the local political parties prefer to form minimal winning and minimum parties coalitions, but not the smallest coalition that is possible. Coalitions are also more likely to form when they represent the incumbent coalition. Finally, political parties prefer congruent coalitions with the federal and regional government