Ecological Aspects of Host Colonization: Coaggregation, Osmoadaptation, and Acid Tolerance or Resistance

Abstract

This chapter describes three examples of adaptations that are important for bacteria to colonize human hosts. It provides a short preview of coaggregation, osmoadaptation, acid resistance and tolerance. A complex microbial community exists within the human gingival crevice, the space below the gum line between tooth surface and epithelial tissue. A combination of bacterial activities and host inflammatory responses leads to death of tissues around the tooth, destruction of collagen connecting tooth to bone, loss of bone, loss of tooth, and various forms of periodontal disease. A hyperosmotic stress can occur when bacteria are transported by ingestion from a contaminated drinking water source to a site in the human lower bowel or when bacterial cells infecting the urinary tract are exposed to fluctuating urine osmolalities. Escherichia coli and Salmonella cells can become acid tolerant (a term used to indicate that they have an inducible insensitivity to acid). A nonlethal exposure to mild acid conditions will transiently protect these species against lethal, more severe acid exposures. Inflicting damage on host tissues and evading immune surveillance are not only events, but defining properties in the life of a pathogenic bacterium. Equally important are characteristics essential for a pathogen to grow within a host and to access new hosts. Coaggregation, osmoadaptation, and acid tolerance and resistance are not essential for routine growth of bacteria in culture.