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Bacterial enteric pathogens are responsible for a tremendous amount of foodborne illnesses every year through the consumption of contaminated food products. During their transit from contaminated food sources to the host gastrointestinal tract, these pathogens are exposed and must adapt to fluctuating oxygen levels to successfully colonize the host and cause diseases. However, the majority of enteric infection research has been conducted under aerobic conditions. To raise awareness of the importance in understanding the impact of oxygen, or lack of oxygen, on enteric pathogenesis, we describe in this review the metabolic and physiological responses of nine bacterial enteric pathogens exposed to environments with different oxygen levels. We further discuss the effects of oxygen levels on virulence regulation to establish potential connections between metabolic adaptations and bacterial pathogenesis. While not providing an exhaustive list of all bacterial pathogens, we highlight key differences and similarities among nine facultative anaerobic and microaerobic pathogens in this review to argue for a more in-depth understanding of the diverse impact oxygen levels have on enteric pathogenesis.

The human gut microbiota is inextricably linked to health and disease. One important function of the commensal organisms living in the intestine is to provide colonization resistance against invading enteric pathogens. Because of the complex nature of the interaction between the microbiota and its host, multiple mechanisms likely contribute to resistance. In this review, we dissect the biological role of short-chain fatty acids (SCFA), which are fermentation end products of the intestinal microbiota, in host–pathogen interactions. SCFA exert an extensive influence on host physiology through nutritional, regulatory, and immunomodulatory functions and can also affect bacterial fitness as a form of acid stress. Moreover, SCFA act as a signal for virulence gene regulation in common enteric pathogens. Taken together, these studies highlight the importance of the chemical environment where the biology of the host, the microbiota, and the pathogen intersects, which provides a basis for designing effective infection prevention and control.

Publisher Summary This chapter examines the diverse geochemical and microbial reactivities of humic substances (HS), the role that these complex organics play in a diversity of environments, and their potential applicability to bioremediative strategies. HS are ubiquitous components in the environment and can be readily isolated from nearly all soils, waters, and sediments. They can account for as much as 10% by weight of the total content of many soils and sediments. It is clear that HS interact with microbial populations through a diversity of mechanisms. These interactions may potentially affect the microbial ecology of a specific environment and significantly affect fate and transport of organic and inorganic environmental pollutants. By considering these interactions, strategies for bioremediation of particular pollutants may be improved. HS can be utilized by microorganisms as effective electron acceptors for the oxidative degradation of organic carbon in anaerobic environments. Alternatively, HS in the reduced form can be utilized by microorganisms as effective electron donors for the assimilation of organic carbon coupled to denitrification. These metabolic processes as well as the intrinsic geochemical reactivity of HS are now known to play an important role on the fate and transport of herbicides, pesticides, hydrocarbons, cations, and other important environmental pollutants.