The ecology of Campylobacter jejuni in avian and human hosts and in the environment

Campylobacter jejuni, and its close relative C. coli, are highly successful bacteria colonizing the intestinal mucosa of a wide range of avian and animal hosts, including humans. In general, this colonization is either as a commensal, as in birds, or is an asymptomatic transient infection, as in livestock and in humans in endemic regions. However, in susceptible human populations, infection causes acute bacterial enteritis. The ecology of the organism for each outcome of colonization is considered, and evidence suggests that disease symptoms reflect the unfortunate consequences of the expression of bacterial factors associated with adaptation to the host gut environment. Susceptibility to disease appears to be associated with lack of acquired immunity. Although campylobacters do not grow outside the host, they can remain viable for long periods in water, foods, etc. Under such conditions, the organisms adapt to numerous hostile environmental stresses. Although such stressed organisms may be viable, the infectivity of surviving bacteria becomes severely compromised over time. Thus, the comparison of Campylobacter ecology in different environments suggests that increasing trends in human campylobacteriosis represent an unfortunate consequence of: decreasing human immunity because of reduced exposure to stress-compromised organisms; intensive farming practices creating monocultures of some strains; and improved processing and retail practices increasing the viability of campylobacters in food reaching the consumer.