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The influence of environmental conditions on the infectivity of non-growing Campylobacter jejuni

De invloed van omgevingsfactoren op de infectiviteit van niet-delende cultures van Campylobacter jejuni

Synopsis

Campylobacter (C.) jejuni is a causative agent of gastro-enteritis. Growth of this Gram negative bacterium is restricted to a limited number of environmental conditions. Under conditions where growth of C. jejuni is not possible, e.g. at temperatures below 30 degrees C, C. jejuni can remain viable for a certain period of time, but its culturability decreases. In this study we examined the effect of this loss of culturability on the infectivity in cell-lines. We hypothesised that if non-culturable cells affect the process of infection then the infectivity per culturable cell used in the infection assay is not constant, whereas if only culturable cell are infectious then the infectivity per culturable cell is. C. jejuni was stored for 40 days in nutrient poor and nutrient rich medium at three temperatures. During this period we monitored its culturability, viability and infectivity. A decrease in culturability in time was observed. At low temperature (4 degrees C) and in nutrient poor medium cells remained culturable for longer periods than at higher temperatures (12 degrees C, 25 degrees C) or in nutrient rich medium. Non-culturable cells remained viable, as determined by tetrazolium chloride staining. The absolute level of adhesion and invasion showed a decrease in time. At low temperatures and in nutrient poor medium cells retained their capability to adhere and invade longer than at higher temperatures or in nutrient rich medium. While the absolute level of adhesion and invasion decreased, the infectivity per culturable cell added seemed to increase during the first 5 days of storage at 4 degrees C. This result confirmed our hypothesis that non-culturable C. jejuni can affect the process of infection. However, the result can also be explained by the presence of a limited number of bindingsites for C. jejuni in our testmodel. This suggested existence of bindingsites has great importance for the research into the influence of non-culturable cells on the infectivity. If non-culturable cells are not infectious but can block bindingsites, then they can play a protective role by competing with the culturable cells for the limited number of bindingsites.
 

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