The ability of bacteria to grow within a host is of fundamental importance for the pathogenesis of disease. For successful in vivo growth, pathogens have evolved metabolic processes for thriving in different host environments. These metabolic adaptations are tailored to meet the nutritional requirements of their specific host niche, to compete with each other for carbon and energy sources, and to withstand bactericidal defenses. One prominent example involves the subset of E. coli that causes infections such as urinary tract infections, bacteremia, sepsis, and meningitis. These E. coli strains have adapted to live in the nutrient- and carbon-rich environment of the human gut as benign commensal bacteria.
However, they can quickly switch to a pathogenic lifestyle when they encounter the nutrient-poor, nitrogen-rich environment of the urinary tract. This ability to adapt is key to enabling them to thrive. As extraintestinal pathogenic E. coli move between different microenvironments within the same host, the specific bacterial adaptations that allow them to form both commensal and virulent associations are described. These adaptations are a testament to the remarkable versatility and resilience of these bacteria in the face of the challenges of diverse host environments. Bacterial reproduction occurs through a process called binary fission, in which a single bacterium cell splits into two identical daughter cells.
The amount of time it takes for this division to occur, known as the generation time, can vary widely depending on factors such as temperature and the availability of nutrients. Under optimal conditions, certain food poisoning bacteria can have one division every 10 minutes. However, at lower temperatures around 10°C, the division process can take up to ten hours or even stop altogether. The average time required for common foodborne bacteria to develop under ideal conditions is typically about 20 minutes. When bacteria are in a state of active growth and division, they are said to be in a vegetative state. This rapid multiplication can significantly increase bacterial populations, which is a critical factor in foodborne illness development.
Cells enter a stage known as the death phase when waste products accumulate and the nutrient-rich environment is depleted. This is the point at which living cells cease their metabolic functions and are in the process of death. The cells are lysed and burst open, releasing their internal contents into the surrounding culture. This release marks the beginning of exponential decay and significantly alters the environment. The death phase of cell culture can have tremendous implications, especially in the field of bioprocess engineering. In the process, the cell disintegrates, releasing an abundance of valuable amino acids, protein, polysaccharides, and free fatty acids.
Reference:
** Cynthia Nau Cornelissen, & Marcia Metzgar Hobbs. (2019). Microbiology. Lippincott Williams & Wilkins, [], C.
** Alteri, C. J., & Mobley, H. L. (2012). Escherichia coli physiology and metabolism dictates adaptation to diverse host microenvironments. Current opinion in microbiology, 15(1), 3-9.
** Sebastian. (2013). Bacteria: A Very Short Introduction. OUP Oxford.