Go with your gut: The human intestinal microbiota, international travel, Campylobacter and ESBL-producing Enterobacteriaceae

Up to 100 million people travel annually from industrialized countries to resource-limited ones. Each traveller contains an internal ecosystem composed of tens of trillions of microbes, known as the intestinal microbiota, which has a large effect on health. The microbiota seems to be highly individual and mostly stable but can be significantly affected by several factors. Many international travellers are at high risk of getting infected by Campylobacter , the most common cause of bacterial enteritis worldwide. Campylobacter infection can cause a wide range of symptoms, with varying severity, for reasons largely unknown. Travel also radically increases the risk of colonization by antibiotic-resistant intestinal bacteria, notably Extended spectrum beta-lactamase (ESBL)-producing Enterobacteriaceae (EPE). To date, there are no therapies available for EPE-decolonization. In this thesis, it was investigated whether the bacterial intestinal microbiota affected susceptibility to Campylobacter and if international travel as such had an impact on the microbiota. In a prospective, observational study, 67 healthy Swedes, travelling in groups to countries with a high risk of Campylobacter infection, were followed. The travellers answered questionnaires and delivered two faecal samples before and three samples after the trip. These samples were cultured for enteropathogens and analysed for the microbiota composition. Low diversity of microbiota seemed to increase the risk of Campylobacter jejuni infection, whereas a high relative abundance of Lachnospiraceae might decrease the risk (Paper I). Furthermore, the overall bacterial diversity did not seem to change in connection with travelling. However, the bacterial family Enterobacteriaceae (otherwise connected with inflammation, infection and antibiotic-resistance) was shown to be dramatically increased in abundance immediately after travel, and the family Christensenellaceae (otherwise connected with beneficial health conditions) simultaneously decreased (Paper II). Eight travellers, from two different destinations, were infected with closely related C. jejuni isolates (ST353CC). The bacterial analysis of genomic and phenotypic characteristics revealed that the C. jejuni isolates of the travellers returning from one of the destinations and with more severe symptoms actually showed less pathogenic potential, compared to the isolates of travellers from the other destination and with milder symptoms. However, the trave